as: uss which benefit mankind; radiation energy versus fission · tracers in biology and in industry, ... as he compares the radioactivity. ... application of scientific principles

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INSTITUTIONPUB DATENOTEAVAILABLE FROM

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SE 010 597

Brannigan, Francis L.Living with Radiation. The Problems of the NuclearAge for the Layman.Atomic Energy Commission, Washington, D.C.7071p.Superintendent of Documents, Government PrintingOffice, Washington, D.C. 20402 ($0.70)

EDRS Price MF-$0.65 HC-$3.29*Nuclear Physics, Physics, *Radiation, *RadiationEffects, *Resource Materials, Textbooks

The text takes a practical approach to theunderstanding of industrial radiation hazards. It is intended for thelayman who requires a basic understanding of the relationship ofradiation problems to his own field. Discussion includes such topicsas: uss which benefit mankind; radiation energy versus fissionenergy; effects of excessive radiation exposure; external versusinternal radiation problems; air sampling techniques; containmentprocedures; contamination and containment procedures; decontaminationtechniques; radioactive decay; atomic fission process and control;transmutation; and atomic fission criticality hazards and control.Appendices include definitions for 101 atomic terms and tables ofcommonly used radioisotopes. (JG)

U.S. DEPARTMENT OF HEALTH,EDUCATION & WELFAREOFFICE OF EDUCATION

THIS DOCUMENT HAS BEEH REPRODUCED EXACTLY AS RECEIVED FROMTHE PERSON OR ORGANIZATION ORIG-INATING IT POINTS OF VIEW OR OPIN-IONS STATED DO NOT NECESSARILYREPRESENT OFFICIAL OFFICE OF EDU-CATION POSITION OR POLICY

11 A

If

FUNDAMENTALS

The PROBLEMS

OF THE

NUCLEAR AGE

for the LAYMAN

Prepared by

FRANCIS L. BRANNIGAN

SAFETY & FIRE PROTECTION BRANCH OFFICE OF INDUSTRIAL RELATIONS WASHINGTON, D. C.

UNIT ED STATES ATOMIC ENERGY COMMISSION

.11STROIY,I,11110

PREFACE

Part I of "Living With Radiation" presents the essence of what has beenfound by extensive field experience to be a practical approach to the under-standing of the industrial radiation hazard.

It is intended for a layman who requires a basic understanding of therelationship of the radiation problem to his own fieldbecause of its directbearing on his own work or because he is an instructor of others.

The technically educated reader should bear in mind that the intentionis not to make a technician out of the student, rather it is to present onlywhat he needs to know, without the frustration engendered by the precisedetailed exposition necessary to the scientist.

The material has been used successfully as the basic foundation of the3-day Instructor Courses conducted by the Safety and Fire Protection Branchfor fire and police instructors and others with a real need for practicalinformation.

Texts applying the material in Part I to specific problems in fields ofwork such as fire, police transportation, etc., will be issued as a series ofParts II. Each Part II will relate the basic material to one particular field

Constructive comments and suggestions are invited.

For sale by the Superintendent of Documents, U.S. Government Printing OfficeWashington, D, a 20402 - Price 70 cents

iii

TABLE OF CONTENTS

Page

PREFACE iii

Chapter IINTRODUCTION 1

(A layman's approachWorking concepts versus detailed definitions)

Chapter IITHE BENEFITS OF THE ATOMIC AGE 3

(Benefits justify hazard -Uses which benefit mankindRadiation energyversus fission energyMan will learn to live with this hazard as with others)

Chapter PROBLEM OF HAZARD 10

(Why is any risk justifiedUnavoidable background medical exposureRelationship to other riskshazard evaluation a conscious or unconsciousprocessEffects of excessive radiation exposureExternal versus internalradiation problems)

Chapter IVEXTERNAL RADIATION PROBLEM 13

(Long range highly penetrating radiation similar to X-raysEffect on bodyMatter is mostly empty space How. harmful is radiation exposureUnitsof measurementLevels of injuryGenetic effectsLong term exposuresThe banking concept)

Chapter VPROTECTION FROM EXTERNAL RADIATION 23(Time, distance, shieldingCuriesSome practice problemsShort range

external radiationsHow things do not get radioactiveNames of radia-tionsRads, RBE, Rems)

Chapter VIINTERNAL RADIATION PROBLEMS 33(How radioactive material enters the bodyWhat happens to it in the body

Origin of permissible levels)

Chapter VII--PROTECTION FROM INTERNAL RADIATION HAZARDS 35(Air sampling techniquesContainment proceduresBio-assayEmergency

situations)

Chapter VIIICONTAMINATION 39(Nature of hazardPrevention of spreadHalf-livesDecontamination

techniquesPreplanning for emergencies)

Chapter IXINSTRUMENTS AND PERSONNEL DOSIMETRY 42(Geiger countersIonization chambersScintillation countersFilm badges

Pocket electroscopes)

Chapter XA LITTLE RADIATION PHYSICS 44(Some unanswered questionsThe nucleusProtons-neutrons-isotopesRadio-

active decayOrigin of radiations)

vi Contents

Page

Chapter XI ATOMIC FISSION 49(Fission versus radiationAtomic fission process--Controlling fissionRadio-

isotopes by neutron capttireTransmutationCriticality hazardsCriti-cality control)

APPENDIX A 59(101 Atomic terms and what they mean)

APPENDIX B 64(Tables)

BIBLIOGRAPHY___ 65

Chapter I

INTRODUCTION

The subject of ionizing radiation and itseffects is extremely confusing to the averagelayman. Much that appears in newspapers andmagazines is written with an eye to the sen-sational and presents the hazard of radiationas if its unique aspects make it impossible tounderstand and so set it apart from all theother hazards of normal, everyday, existence.The result is that the average individual feelsthat only a highly skilled technician can under-stand this extremely complex subject, and heeither ignores the entire subject and the pos-sibility of hazard to himself, or, on the otherhand, has an unreasonable fear of radiationinjury in situations where in fact no real hazardexists.

The purpose of this text is to present to youa layman's understanding of the hazards ofradiation. You, in turn, can then pass on theinformatiop about the hazards and the precau-tions to be taken to avoid unnecessary expo-sure. As an end result, the radiation hazardwill be placed in proper perspective to theother hazards of our workaday world.

You will learn some fundamental necessaryfacts and many common misconceptions willbe cleared away. All of the material will bepresented in a manner and in a language whichyou can, if you choose, adopt as your own.Many people, attempting to teach this subject,feel that it is first necessary to define all of theappropriate terms in the field of physics sothat the student will have an accurate under-standing of precisely what each word means,and from that point go forward to an under-standing of the subject. The difficulty is thatthe instructor has spent many years buildingup in his mind an exact understanding of whatparticular words mean, but the fact that hedefines such a word for the students does notmean that the word means the same thing to

the students as it does to the instructor, or thatthe student immediately has an exact conceptof what the instructor means when he uses aparticular word.

Think of the difference between a translatingknowledge of a foreign language and knowingthe language well enough to think in it. Ifyou go to a foreign country with only yourhigh school ability to translate the language,you find that the person to whom you speakpresents so many words and ideas so rapidlyto you that you are completely overwhelmed,and that by the time you attempt to finish thetranslation of the first idea, he has gone onto several more, and you are hopelessly lost.

In this presentation, we will not necessarilyprecisely define our terms, but we will try touse working concepts, because this is the nat-ural method which we .followed in learning inchildhood. When, as a child, we discoveredin the living room an object that was flat onthe top and had some legs on it, we went tomother and said, "What is this?" She said,"A table." From that point on, we had a con-cept of a table. We know what a table is, weknow also what is not a table, yet we wouldfind it difficult to define a table in preciseterms. "A flat surface with 4 legs," you say?There are tables with any number of legs. "Aflat surface?" A draftsman works on a draft-ing table, which has a sloping surface. Yet,despite the fact that we cannot define it, weall are quite sure that we know what a tableis, because we have a working concept.

We will get some working concepts of physi-cal phenomena which will serve quite well toaccomplish our purpose. In some cases, wemay not be as precisely accurate as the physi-cist must be, but we will be accurate enoughto accomplish our purpose.

6

1

2 Living With Radiation

The atomic age promises many wonderfulbenefits for mankind. The use of atomicpower, the use of radioactive materials astracers in biology and in industry, the use ofmassive doses of radiation in the cure ormalignant diseases, the use of radiation to killoff bacteria in food so that food may be pre-served longer, the use of the energy fromradioactive material in certain chemical proc-

esses to bring about the development of newand useful productsall these things promisegreat benefits to mankind, yet one single factmakes it necessary for us to undertake ourstudy.

Radioactive materials emit energy which hasthe power to damage living tissue.

Chapter II

THE BENEFITS OF THE ATOMIC AGE

Since there is, admittedly, some hazard inthe use of radioactive materials, let us examinebriefly the benefits to mankind which flow fromthe development of nuclear energy.

There are many, many useful applications ofradiation for the benefit of mankind. In thisdiscussion we cite only a few, but we do at-tempt to break them down categorically sothat, as you learn of other uses of radioiso-tope-4 you may be able to fill them in undertheir proper headings. This categorical break-down is useful in eliminating confusion. Youwill find, for instance, a great deal of confu-sion between the diagnostic and therapeuticuses of radioisotopes; that is, the use ofradioisotopes to discover the nature of a par-ticular illness as distinguished from the useof radioisotopes to cure the illness. In somecases, as soon as a person hears that radio-isotopes are involved, there is a natural in-clination to jump to the conclusion that thepatient necessarily has cancer because of thefact that the use of radiation in the cure ofcancer is very widely known to the public.

The first use that we find for radioactivematerials i8 that they send out signals whichcan be detected by electrical or chemical means,and this use, of itself, makes them extremelybeneficial to mankind.

For instance, it makes it possible to tracebiological processes in man, animal, and plants.The thyroid gland is a very important glandin the body. It is well known to medical menthat the thyroid gland will take up practicallyall of the element iodine which enters the body.If we introduce radioactive iodine into thebody, is it still, chemically, iodine, and, there-fore, it will go to the thyroid gland. By theuse of electrical counting devices, the surgeoncan determine whether the thyroid is properly

functioning, as he compares the radioactivityrecorded with what it should be. The radio-active iodine is not doing anything for thepatient or doing anything to the thyroid con-dition from which the patient is suffering. Inthis case, it is simply being used as a tool totell the doctor whether the thyroid is func-tioning properly. What to do about thethyroid condition is another matter entirely.

There are many, many other uses of isotopesas tracers in medicine. New uses are beingdiscovered every day.

One of the most pressing problems facingthe world today is the explosive growth ofpopulation and the necessity for feeding, ade-quately, more and more people every year. Theapplication of scientific principles to the pro-duction of foodstuffs for mankind is only inits infancy. Much of our feeding of foodanimals and plants intended for human orfood animal consumption is, in truth, done atrandom. By the use of radioactive tracers,scientific knowledge can take the place ofguesswork, and we will be able to producemuch more food. This is of the utmost im-portatice in a world in which many people goto bed hungry every night. As a typical in-stance, the use of calcium and phosphorustracers have provided information which willenable livestock feeders to get maximum effi-ciency from feed by more careful control ofthe calcium-phosphorus ratio of the diet, andby eliminating high concentration of elementswhich affect adversely the absorption of theseelements.

Radioisotopes have proven extremely usefulin determining the nature and extent of pos-sible toxic residues in or on agricultural com-modities from the use of insecticide compounds.Work with radioactive isotopes has shown that

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many fertilizers can be applied directly to theleaves of plants and be absorbed through theleaves. It has also shown that fertilizer, takenup through the root system, can be leachedfrom the leaves by rain.

Just as we can trace biological processes inman and plants and animals; we can tracephysical processes by making some of the ma-terial radioactive, or by including radioactivematerial similar to the materials which wewish to trace. A simple example is the useof radioactive iron to check engine wear. Thepiston ring is made of radioactive iron. Asthe piston ring wears, the radioactive iron isdetected in the lubricating oil system. . An-other use is the addition of radioactive isotopesto the product transported in oil pipe lines.The radioactive material is introduced at theinterface, between two different shipments, andprovides a means by which one shipment canbe differentiated immediately from the nextshipment.

It is very important to us, at times, to knowexactly how dense a material is and whetherthe density is uniform throughout the mate-rial. An example of this is the examinationof piping which must hold against very highpressures. When such piping is hydrostati-cally tested, we have simply determined thatthe piping did not fail at the pressure reachedon the date of the test. Hydrostatic testingdoes not show us whether there is a potentialfault which may fail at a later, date. We arefamiliar with the fact that valves and othersuch fittings can be X-rayed to determinewhether or not there is any defect in the bodyof the valve. It is impossible to take an X-raymachine into the field. to make an X-ray of aweld in a pipe.

Radioactive materials are used for this pur-pose. Radioactive cobalt, for instance, is in-

... s.ert.ed .intp the_ pipe. M ..thelneation,a.The weld is surrounded with X-ray film. Thefilm is sensitive to the radiation coming throughthe pipe. If some parts of the weld are notas dense as the rest of the weld, less radiationwill be absorbed, the film will receive more

radiation, and, therefore, the film will bedarker.

The difference in absorption of radiation byvarious thicknesses of materials is also usedin so-called thickness-guages. These are ex-tremely important in industries such as metal-working, where metals must be rolled to anexact thickness at high speed. If the manu-facturer waits to determine whether the ma-terial is the proper thickness until the entireroll has been manufactured, he may find thathe has a serious loss. The thickness-gaugemakes it possible to determine immediatelywhether the material is being rolled to theproper thickness.

All of these uses are applications of thefact that radioactive materials send out signalswhich can be detected either electrically orchemically.

The next category of use for radioisotopesis the fact that they have the characteristicof making the air electrically conductive. Theaccumulation of static electricity is a serioushazard in those areas where an explosive vapor-air concentration may exist. Static electricityis also a nuisance industrially because it makesthings stick together. Static electricity canbe removed by grounding the equipment, or, insome cases, by surrounding it with a humidatmosphere. In some uses, however, neither ofthese methods is satisfactory.

In the use of radioactive static eliminators,the rays from the radioactive material ionizethe air, and, thus, an invisible path is pro-vided through which the electricity can flowto ground. It is not necessary that there beany contact with the material.

Another very important use of radioactivematerials is the fact that they emit energylehiekeanbring about -the destruction, of livingcells. It is in this property that we find theentire hazard of the use of radioactive mate-rials. However, for the moment, let us passby the hazard, and let us consider the bene-ficial effects.

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A simple description of a cancer is that itis a group of cells growing much too rapidly.Radiation is used to kill off the rapidly grow-ing tissues, and, therefore, bring about a cure,or, at least, an alleviation of the cancer. Youwill find, however, that there is much confu-sion on this subject, and that there are peoplewho believe that there is a direct relationshipbetween radiation and cancer, as such. Forinstance, a man employed on a pipeline inTexas where radium was being used for radi-ography of welds knew that radium was usedto cure cancer. His mother-in-law had can-cer. He took the radium home in his pocketintending to use it to cure his mother-in-law'scancer. Contrary to what he apparently be-lieved, the radium made no distinction be-tween the sound tissue of his leg and hismother-in-law's cancer. The result was thathe received severe radiation burns to his leg,necessitating its amputation. This confusionmay bring about other instances of this type,and radiation sources, which might be acces-sible to people who have a very limited knowl-edge. of their use and hazard, should becarefully controlled to prevent such incidentsfrom taking place.

Another use for the energy from radioactivematerials to destroy living tissue is in thesterilization of food and drugs. Food anddrugs are sealed in moistureproof wrappersto prevent any contact with the outside air.They can then be subjected to massive dosesof radiation so that all living organisms inthe package are killed off.

If all of the organisms are killed off, thefood is sterilized. If a lesser dose of radia-tion is used, the food can be pasteurized. Thatis, not all of the organisms are killed off, butsufficient are killed so that the food can bestored for a reasonable time without destruc-tion by bacteria. The food itself is not radio-active any more than you are radioactive afteryou have been X-rayed. There is, of course, agreat deal of experimental work yet to be done.In some foods, there are very marked changesin color and flavor. In other foods, the changes

are much less pronounced. The QuartermasterCorps of the Army, which is responsible forfood research for all of the Military Services,is actively carrying forward a research pro-gram.

Radiation sterilization is used in the manu-facture of drugs. Destruction of bacteria byheat in many cases isn't practical because theheat will also damage the drug. Radiationkills off the bacteria without raising the tem-perature of the drugs.

The next use that we find for the energyfrom radioactive materials is that this radia-tion, energy can be used to excite the atoms ofcertain materials. We are all familiar withradium-dial wrist watches. It is generally be-lieved that it is the radium which glows in thedark. This is not so, but the radioactivematerials emit energy which causes a phosphor,such as zinc sulfide, to glow in the dark.

A much more important use of this phe-nomenon is in the field of chemical processing.By the use of radiation energy, certain chem-ical effects can be brought about, thus givingus a better product. For instance, when poly-ethylene was first developed, it could not besubjected to boiling water temperature. Now,at the proper point in the process, the poly-ethylene is subjected to the radiation energyfrom radioactive materials. This knocks outa couple of hydrogen atoms, which go off asgas, and changes the manner in which theatoms of polyethylene are linked together,producing so-called cross-linked polyethylene.This can be subject to boiling water tempera-ture, and, thus, can be used in many applica-tions as a substitute for glass where the con-tainer must be sterilized, such as for babybottles.

Another use for the energy of radioactivematerials is voltage production. This is thedirect production of electricity from the en-ergy released from the radioactive atoms.Don't confuse this with the indirect productionof electrical energy in power reactors, where

1.

Living With Radiation

we convert the fission energy to heat and thento conventional forms of power. The quan-tity of energy is extremely minute, but theso-called atomic battery does have uses wherea dependable source of elecrical energy insmall quantities is required.

Radiation, Energy V8. Fission Energy

In all of the uses thus far, we have beendiscussing the use of the energy naturallyemitted by the decay of radioactive materials.Some of these uses are shown in figures 1and 2.

Certain materials have the characteristic ofbeing able to emit bits of matter, which, whenthey strike other atoms of the same matter,cause those atoms to break open and emit morebits of matter which continue the so-calledchain reaction process. The thing that makesthis useful to mankind is the fact that, whenthese atoms are split open, a certain amountof the, energy, which has been holding theatom together, is released, and this energycan be harnessed. This is fission energy, andshould not be confused with radiation energy.The regrouping of the atomic material alsomakes new atoms, many of which are radio-active. Therefore, we get both energy andnew arrangements of the atoms, that is to say,new elements.

We may be seeking, primarily, the energyrelease, as we are in a power reactor or inan atomic b%nnb. As a byproduct, we will getthe new atoms, which are called fission prod-ucts. Some of these fission products are dan-gerously radioactive. In an atomic reactor,the fission products must be removed peri-odically, and the problem of how to handlethem creates one of the problems of the useof atomic fuels.

In a production reactor in which we arecreating a new element on a "mass production"basis, such as the plutonium production re-actors at Hanford, or in a research. reactorwhere we are creating new elements for anyof the applications of radioisotopes which we

discussed previously, energy is also liberated.In many cases, it is not possible to use thisenergy economically, and, therefore, it is sim-ply wasted by being absorbed in the form ofheat by air or water.

The atomic fission, process, therefore, is usedto make the radioactive materials which areuseful to us in the ways which we have dis-cussed earlier in this section, or for the gen-eration of electrical power. Electrical poweris the basis of our standard of living. Weneed only to think back to our own childhooddays and to the limited use of electricity inour homes. The author remembers the furorsome years ago when the local utility companyproposed a minimum electrical charge basedupon the use of 10 kilowatt hours per month.There was a great public clamor on the basisthat this charge was entirely unjust to thethousands in the city which did not use this"tremendous" quantity of electricity eachmonth.

While the use of electrical energy to main-tain our standard of living is more apparentto us in the use of household appliances, ac-tually, it is in the industrial use of electricityfor production that we find the real basis ofour high standard of living. The developmentof alternating current made it possible to useenergy at quite some distance from the pointwhere it was created. During peak water-flowtimes, for instance, electrical power generatedby hydroelectric facilities at Niagara Falls istransmitted over the wires to New York Citywhere it is used.

There is an interesting historical parallelbetween radiation and electricity. When Teslaand Westinghouse developed the use of alter-nating' current, they were violently opposed byEdison's associates. As a matter of fact, anadvertising campaign featured the fact thatthe State of New York was using alternatingcurrent to execute criminals, thus "proving"alternating current was much too unsafe tobe used.

Man needed alternating current for the de-velopment of his standard of living, and he

13

The Benefits of the Atomic Age 9

learned to handle it safely. Man needs thepeace time uses of atomic energy, and he willlikewise learn to handle them safely.

The achievements of the Nautilus and ourother atomic-powered submarines are breath-taking, even in this day of Sputniks and moon

rockets. The fact that the very first atomicsubmarine is a highly efficient operational unitof the fleet can be appreciated more if werealize that it is equivalent to Robert Fultonhaving designed and built the Queen Mary ashiF first ship rather than the Clermont.

14

Chapter III

THE PROBLEM OF HAZARD

Radioactive materials emit energy which hasthe power to damage living tissue.

The relationship between this property ofradioactive materials and the problem of usingthem for mankind's benefit can best be setforth in the following manner :

All radiation can do damage to the body ifreceived iv. Sufficient quantity.

Within certain limits, damage can be re-vared by the body so that there is no apparenteffect.

Therefore, when it is known that these lim-its can be maintained, it is reasonable for peo-ple to expose themselves to radiation in orderto accomplish necessary work.

But, it follows that the degree of exposureshould be related to the importance of thework being accomplished.

That is nice philosophy, you say ! But Idon't care to be exposed to any of this radia-tion hazard. I have heard all sorts of thingsabout it, and I don't want to take any chances,and I don't want any exposure to radiation atall. Unfortunately, we cannot avoid exposureto radiation. We are all exposed to radiationfrom outer space, cosmic radiation, which in-creases in intensity as We go up in altitude.For instance, in Denver, Colo., the mile-highcity, we would' receive twice the radiation fromcosmic rays that we would receive at sea level.Let's get away from cosmic radiation and godown deep in a mine where no cosmic radiationcan penetrate. We still haven't solved theproblem, because then we are exposed to radia-tion from radioactive material in the earth'scrust. In addition, there are radioactive ele-ments within the make-up of our own bodies,elements that have been radioactive from thebeginning of time, such as radioactive potas-sium, radium, and radioactive carbon. Ourbodies also tend to concentrate radioactive ma-terials that we take into our bodies, particu-

10

larly from the water which we drink. Water,in some parts of the country, particularly fromsome mineral springs, has appreciable radio-activity. So, from the beginning of time, manhas been exposed to inescapable natural radia-tion.

In addition to the natural background ofradiation, the population as a whole receivesa certain amount of radiation from medicaldiagnostic and therapeutic procedures. It isobvious from our basic premise that radiationcan damage living tissue, that some of thismedical and dental radiation may have someharmful effects. However, we balance thisharmful effect against the good we expect toaccomplish from the medical procedure. Ifwe find a specific medical procedure in whichthe hazard is not outweighed by the good re-ceived, the logical course is to modify thisspecific procedure, not to do away with allradiation exposure.

An example of foolish and unnecessary ex-posure to radiation is the use of shoe-fittingmachines .which fit children's shoes by the useof X-rays. These are a hazard, not only to thechild, but to the shoe clerk. No useful purposeis served which could not be served by othermeans, and in many jurisdictions these deviceshave been outlawed.

Probably the chief error in much of our cur-rent thinking about radiation hazards is thefailure to relate radiation hazards to the otherhazards of human existence. All human ac-tivity involves risks. Some of them are phys-ical, such as the hazard of being hit on thehead with a heavy object dropped from above.Some hazards are more mental than physical,such as those of the advertising executive orplay producer, who is under the constantstrain of delivering completely satisfactorywork or suffering the penalty of being ruth-lessly eliminated. Consciously or not, when we

r

The Problem of Hazard. 11

select our field of work, we make an appraisalof the hazards involved, along with the otherfactors, such as pay, general working condi-tions, prospects for advancement, security ofemployment, which we consider. Each occu-pation has its own peculiar hazards, inherentin the nature of the work. In controlling thehazard, we attempt to reduce the probabilityof accident to a minimum but cannot guar-antee absolute freedom from risk.

When thinking about radiation hazard, how-ever, some people seem to regard it as a hazardapart from all other hazards, and demand thatwe be absolutely safe from it. In no field ofhuman existence is there absolute safety. Ineverything that we do, we weigh the hazardagainst the good to be accomplished, consci-ously or unconsciously, and make a determin-ation.

We are, for instance, all quite familiar withthe fact that serious diseases can be spreadfrom person to person by improperly washedtableware. Yet, most of us would consider aman who went. into a restaurant and applieda sterilizing solution to the tableware offeredto him before he used it, to be somewhat neu-rotic, to say the least. In general, we haveweighed the risk and found that it is so slightthat. we prefer to ignore it.

However, if a violent epidemic were to breakout in our city, we might well consider thatwe should take such precautions, and that aperson who wouldn't take such precautions islacking in common sense and good judgment.

When we drive on the highway, despite the'fact that we might maintain our own auto-mobile in perfect mechanical condition, de-spite the fact that we might be a truly defen-sive driver and mentally drive not only ourown car but the other cars that the defensivedriver must "drive," situations can arise inwhich we, and those dear to us, can be maimedor killed under circumstances entirely beyondour control. The 'only control we have is tostay at home. Yet, while thousands are killedand maimed on our highways, few of us re-frain from driving automobiles or riding in

automobiles because of this terrible accidenttoll. We have weighed the hazard against thegood and made our decision.

If a man doesn't care to accept the exposureto radiation incidental to employment in anatomic energy plant when all of the necessaryprecautions have been provided and his radia-tion exposure is no more than the maximumpermissible level, there is only one thing forhim to do. He should find other work, thehazards of which he is willing to accept.

The safety record of the atomic energy pro-gram is phenomenally good. Over a 15-yearperiod, with thousands of people engaged inextremely dangerous operations, including vastconstruction projects carried on with tremen-dous speed, the overall safety record compareswith the best of American industry. The fatalaccident record is less than half of that of thebest of American industry. Although 200people have been killed in the program, only3 were in accidents involving radiation. Theothers were killed in what we sometimes call"normal" industrial accidentsfires, falls, elec-trocutions, motor vehicle accidents, and thelike.

The effects of excessive radiation exposureon the body are manifested in several ways.

Radiation Sickness

This is a sickness produced by a massiveoverdose of penetrating external radiation, andit causes nausea, vomiting, diarrhea, malaise,infection, hemorrhage, and, of course, if seriousenough, can cause death.

Radiation Injury

Radiation injury consists of localized in-jurious effects, generally from overdoses of lesspenetrating external radiation and most oftento the hands because contact is usually withthe hands. This can cause burns, also loss ofhair, and skin lesions. Genetic damage is also .

a form of radiation injury.

16


Radioactive Poisoning

Radioactive poisoning is illness resultingwhen dangerous amounts of certain types ofradioactive materials enter the body, causingsuch diseases as anemia and cancer.

When we look at the foregoing, we realizethat we can get into trouble with radiationby two entirely different means. One, byradiation originating from a source outside thebody and coming at the body from the outside;the other by exposure resulting from radio-active materials which have been taken intothe body. It is almost obvious to us that pre-cautions against one type of hazard will notbe particularly helpful in protecting againstthe other type of hazard, and that, in fact,the radiation problem is made up of two sep-arate problems.

This is indeed the case. As a matter of fact,certain radioactive materials are no hazard atall outside the body. However, if we got the

same materials inside the body in sufficientquantity, we could have a case of radioactivepoisoning.

Therefore, it is fundamental to our under-standing to realize that the radiation problemis not one problem, but two problems, theproblem of external radiation, and the prob-lem of internal radioactive poisoning. Theprecautions that we take in various exposuresto radiation hazards depend upon which haz-ard is present. Of course, in a given situation,we may have both types of hazards. Seefigure 3.

To make our study easier, we will stick tothe subject of external radiation hazards en-tirely for the next part of our discussion.When we have completed this subject, we willthen take up the problem of the internal radia-tion hazard. Along the way, we may learn alittle about the nature of radiation itself, butour prime interest is in learning how to livewith the hazard.

Some radiation goesthrough the body like *Rays...

We can receive radiation byswallowing or breathing

radioactive materials....

FIGURE 3

Chapter IV

EXTERNAL RADIATION PROBLEM

The external radiation hazard comes in twoforms :

1. Long-range, highly penetrating externalradiation.

2. Short-range, less penetrating externalradiation.

We will consider the long-range, highlypenetrating external radiation first.

We are talking about a type of radiationsimilar to X-rays, consisting of pure energywith no mass. These rays originate from someradioactive materials outside the body, andcome at the body like a shower of arrows ora beam of light. In order to simplify ourproblem, let us think of one ray at a time.Each ray is a bundle of energy. It penetratesthe body to some depth or other before it doesits damage and the energy of the ray is spent.(The effect of radiation on the body is, ofcourse, a little more complex than this, butthis concept will admirably serve our purpose.)

Observe the figure of the man in figure 4.The rays come at him from the radioactivesource which is giving off the penetratingradiation. Each one of the rays penetrates toa different depth in the body before it finds itstarget and has its effect on the structure of thebody. Also note that a sizable proportion ofthe radiation passes through the man's bodywithout ever touching him. (These rays dohim no harm.)

At first glance this may seem strange. Forinstance, most of us would agree that lightrays cannot pass through a man's body with-out-touching him, but if-we-place our-fingersover the lens of a strong flashlight, some lightcomes through our fingers. If we stop andthink for a bit, we realize that if it were notfor the fact that some radiation can passthrough the body without touching it, we could

hardly take X-ray pictures. The X-ray ma-chine is pointed at the patient's back, the filmis placed at his chest. If his body stopped all

FIGURE 4

of the radiation, there would be no radiationleft to reach the film. It is obvious that someof the radiation gets through to the film.

Figure 5 is a concept of what water mightlook like .i f. we ronld.magnify it with ascope tremendously more powerful than anyin existence.

Most of us know that water is H2O. Thismeans that the water molecule consists of anatom of oxygen with two atoms of hydrogen

13


tied onto it. Each one of the figures in ourillustration represents a molecule of water.Atoms consist of two parts, a heavy dense corecalled the nucleus, which contains practicallyall of the weight, and very tiny particles calledelectrons that spin around the nucleus like theplanets around the sun.

The trouble with our illustration is that itis not at all to scale. If the nuclei of ouratoms were actually as big as we have shown,the electrons would be many hundred feetaway.

We see that if the electrons are this faraway from the nucleus that the nuclei of thevarious atoms must be relatively quite farapart. This is the case. Yet, when we feel asubstance, when we step on the scale, what weare feeling or what we are weighing is thesum total of the nuclei, these little incrediblyheavy balls of matter spinning around inmostly empty space. These nuclei are so heavy

ELECTRONS

411111h.

that if a child's marble could be made of thismaterial only, it would weigh 37 million tons.

Therefore, we see how it is possible for theray to penetrate quite a distance into the sub-stance before it hits anything.

The rays from radioactive materials do nothit the nucleus in significant amounts; fewof them have enough energy to penetrate tothis hard ball of matter. They do hit the elec-trons, which are spinning around the nucleus, .and the ehergy of the ray is spent. The dam-age done by the rays from radioactive materialsis practically all done by this knocking theelectrons out of the atom, and if enough elec-trons are knocked out of enough atoms, wehave radiation damage. We should, of course,have some appreciation of the numbers in-volved. For instance, there are 6 sextillionatoms

6,000,000p00,000,000,000,000

in a single drop of water.

MOEN NUCLEI

441111.

"MOSER NUCLEI

FIGURE 3

0

_ N4

External Radiation Problem 15

It is a hard thing to discard our concept ofthings being solid and accept this new conceptthat matter is mostly empty space, but it isessential if we are going to understand thisradiation business. So let us try another ap-proach.

Consider a series of rows of air-jets, perhaps20 rows of jets with 20 jets in a row, making atotal of 400 air-jets in a square. The variousjets are staggered within the square. On eachair-jet a ping-pong ball is balanced. Thisping-pong ball goes up and down as the air-jets are turned on and off at random. If westand close to this setup, we will see the in-dividual ping-pong balls. If we move away300 feet, we will not see the individual balls,but what would appear to be a solid whitemass. However, just because this appears tobe a mass, we know that this does not make ita mass.

The fact that matter appears to be solid, wenow know, does not prove this to be true. Allmatter consists of little hard balls of materiallinked together by trading and sharing elec-trons floating around in what is mostly emptyspace. It is quite easy for the rays to pene-trate various depths before they find an elec-tron to hit. If we were to fire a rifle at our"solid" white target from 300 feet, we knowthat it would be impossible to say in whichrow we would get a hit on the ping-pong ball.As a matter of fact, it would be quite possiblefor the bullet to pass through the ping-pongballs without doing any damage at all.

If we substitute a machine gun for our rifleand consider that the bullet would disintegrateupon hitting one ball, it is easy to understandthat while our hits would be scattered, wewould get more hits in the front rows, andfew hits in the back rows. If we carried onenough experiments we could arrive at tablesgiving us the percentage_of hits. to be expected -

in each row.For penetrating external radiation, such

tables are available to the radiologist. Theyare called dose depth distribution tables, butwe need not get that technical.

This radiation effect is going on in our bodiesconstantly. We are constantly being bom-barded by cosmic rays from outer space andrays originating from radioactive materials inthe structure of our buildings, in our bodies,in the food we eat, etc. When an electron isknocked off an atom, the cell of which theatom is a part is damaged. The body's repairmechanism swings into action to repair thedamaged cell. Perhaps this constant bombard-ment from natural backgrclind is doing ussome harm, or, possibly, some good. Nobodyknows one way or the other for sure. In anyevent, we have been able to live with it andadapted to it for many, many thousands ofgenerations.

On the other end of the scale, we know thatexcessive radiation exposure can bring aboutsufficient damage to cause death.

Our problem is to regulate our radiationexposure to the amount from which there willbe no apparent effect. There is no singleanswer to the question, "How harmful is radia-tion exposure?"

A simple illustration helps to prove thispoint. Slap your hand on the desk, smartlyenough to make it sting. There is no visibledamage, but I am sure that you will agree thatpossibly some cells in the palm of your handhave, in fact, been damaged by this blow. Ifyou strike your hand somewhat harder on thedesk, visible damage in the form of black andblue marks will show up. The body will gen-erally recover from this damage after someeffort on the part of the body repair systemto rebuild the damage, and there will be noapparent aftereffect. A harder blow wouldcause broken bones which would not healproperly unless given adequate medical atten-tion. The severest degree of damage, of course,would be to break the hand off at the wrist,because this. damage -would be- irrepaiuble.

Just as there is no simple answer to the ques-tion of how harmful it is to slap your handon the desk, there is, likewise, no simple singleanswer to the question of "How harmful isradiation exposure!"

20


The Roentgen

We have seen that, on the one hand, it ispossible to have radiation exposure so smallthat it has no apparent effect, and on the otherhand, it is possible to receive sufficient radia-tion exposure to cause death. It is, therefore,necessary that we have some unit of measure-ment with which to measure radiation exposureso that we can determine what the acceptablelimits are and be sure that we are operatingwithin those limits.

The unit of measurement for penetratingexternal radiation exposure is the roentgen (themilliroentgen is 1/1000 of a. roentgen). It isan arbitrary unit of measurement. Its exactdefinition is of significance only to experts.Our interest lies in how many roentgens aretoo many.

Single Exposures

It is impossible to say how many roentgensit will take to kill any specific individual be-cause wo all vary in our resistance to anyattack upon the body, whether it is by radia-tion, electricity, poison, injury, diseases, etc. Itis quite certain, however, that no human beingcould survive 1,000 roentgens of total bodyradiation delivered in a short space of time.

Roth of these conditions are most important.The effect of 1,000 roentgens of radiationdelivered to the total body is by no means thesame thing as 1,000 roentgens delivered to asmall portion of the body any more than athird degree burn of the palm of the hand isthe same thing as a third degree burn of alarge area of the body.

Similarly, the short space of time is an im-portant part of the definition. The short spaceof time is.,defined as..24 hours,...or leas__ Theability of the body to withstand any insult is,of course, increased if the same amount ofin ;kilt given to the body is spread out over alonger period of time. Whiskey can be poison,but many people, apparently without any de-

monstrable injury, can drink an ounce of whis-key each evening before dinner over an extendedperiod of time. If, however, a person attemptsto consume a three month's quota of whiskey inone sitting, he will probably die of alcoholicpoisoning because the body has not been givensufficient time to recover from the poison.

The dose it takes to kill one, specific individ-ual is not a good measure of the fatal doseto others because of individual differences. Theterm that is used in this field is the so-calledmedian lethal dose, or LD/50. This is thedose that it takes to kill 50 percent of thesubjects. The LD/50 for penetrating externalradiation is about 500 roentgens delivered tothe total body in a short space of time (24hours or less).

This means that if a representative sampleof the population were subjected to 500 roent-gens of total body radiation within a 24-hourperiod, approximately 50 percent of these peo-ple would die, and the other 50 percent wouldrecover.

At about 200 or 250 roentgens of total bodyradiation in a short space of time, we wouldexpect to find the first death.

From 100 to 200 roentgens of total bodyradiation in a short space of time, we wouldexpect nausea, fatigue, vomiting, and sickness,but no fatalities.

At about 50 roentgens of total body radia-tion in a short space of time, we would getsome slight temporary blood changes whichwould reverse themselves with the passage oftime. The person would have no symptomswhich he himself would notice.

At 25 roentgens of total body radiation ina short space of time, we would probably findno detectable effect.

Figure 6 illustrates these levels.Remember:.. that all of these. figures..are on

the basis of total body radiation within ashort space of time. We should also note thatit is quite difficult for a person to receive highradiation exposure unless there is gross viola-tion of simple safety precautions.


EFFECTS OF EXTERNAL RADIATIONTOTAL BODY EXPOSURE WITHIN 24 HOUR PERIOD

50 017Half Die

200-250r First Death

100r: Nausea, Fatigue

50r: Slight Temporary Blood Changes

25r: No Detectable EffectFIGURE 6

Continuous Et.RpO8Ure8

Thus far, we have been thinking about asingle incident of radiation exposure, one fromwhich the man dies, gets sick and recovers, orreceives no apparent effect at all; the sort ofproblem that is very similar to the ordinaryinjury situation. A man gets up on a ricketyladder, the ladder breaks, and he falls. He candie, he can be injured and recover, possiblywith some permanent disability, or he may befortunate and have no ill effects at all. Inany case, the incident is closed, the effect onthe body is accomplished, and that is prettymuch the end of it.

There is another possibility with radiation,howeverthe problem of repeated small ex-posures to radiation over an extended periodof time. What are the effects of this on theindividual and what sort of radiation safetylevels must we have so that there will be noappareat effect and so that the hazard will be

consistent with the other hazards of industryas we know them?

To how much radiation can people be safelyexposed? How can we maintain the radiationhazard consistent with the other hazards ofhuman endeavor?

There are two considerations which we musttake into account. The first is the effect ofthe radiation on the individual himself. Thatis to say, what damage is done to the ino:hdd-ual by repeated small dosages of radiation overa period which might conceivably extend fromthe time that he enters industrial employment.until he retires, perhaps as much as N yearslater?

The other problem with respect to societyis the so-called genetic effectthe problem ofdamage done to the genetic life stream of thepopulation by the exposure of large numbersof individuals to ionizing radiation.

Complicating the whole situation are thefacts that all of us receive background radia-


tion from cosmic rays and naturally occurringradioactivity, that we are all exposed to acertain average level of radiation irom med-ical and dental X-ray procedures, and that weall get a small increase in our backgroundexposure from fallout from atomic weaponstests, no matter by whom conducted. The fig-ures presently used for the regulation of radia-tion exposure in the individual take all of thesefactors into account.

In so far as the direct effect on the individ-ual is concerned, it appears that high, dosagesof radiation received over a relatively shorttime can have some effect on the Hie span ofthe individual. The National Academy ofSciences, National Research Council Reportcites studies of a group of radiologists, someof whom received as much as 1,000 roentgensof X-ray exposure, which show, on the aver-age, a life span 5 years shorter than that ofother physicians. There is, as yet, no conclu-sive evidence that low dosages spread over aperiod of years have any life-shortening ef-fect. On the other hand, there is no evidenceto indicate that there is a level of radiationexpesure below which we can say there is nolife-shortening effect at all.

Radiation,, of course, is not the only factorin causing shortening of life. We have onlyto review in our minds the interviews tradi-tionally conducted by the press with those whohave reached an advanced age, in which thesepersons are asked to what they attribute theirlong life. The answers collectively cover theentire gamut from those things which many ofus believe to be deleterious to things whichmost of us believe to be beneficial. Wouldyou, for instance, say that the widespread useof the automobile causes a longer or a shorterlife span in the average individual? Muchheat and very little light could be generatedin an argument on this subject.

Genetic Effects

The genetic effect of radiation is one of theareas in which the laymen is most completely

r.

confused. We should first dispose of somecommon misconceptions. There is no relation-ship between' the so-called genetic effect andsterility or impotence. Radiation doses so highas to be nearly fatal can bring about sterility,which is the inability to conceive childrendespite normal sexual relations. Impotence isthe inability to carry on sexual relations andradiation has no effect on this.

Another misconception is the idea that allcongenital (present at birth) handicaps aregenetic. Only about half the recognizablecongenital handicaps are genetic in origin; theothers are caused by disease or other factors.

The next misconception that we should clearaway is the idea that there is any direct rela-tionship between an exposure to radiation andthe conception and birth of a defective childin any specific instance. It is true that radia-tion striking genetic material which is usedin the conception of the ilext generation maycause a mutant which may show up in a futuregeneration. However, we cannot determine thecause of any specific mutant. The mutant may,or may not, be caused by radiation, but evenif caused by radiation, we cannot know thesource of the ray. On the other hand, nomeasurable amount of radiation from anysource is so small that we can say positivelyit cannot have a genetic effect. The geneticistnecessarily is concerned not about individualsbut about the population as a whole.

The problem, therefore, is not one of pro-tecting a specific individual but of protectingthe entire population by keeping all exposure toradiation down to the lowest practical limits.

The portion of the population of primaryinterest to the geneticist is that portion whichhas yet to make its substantial contribution tothe next generation. He is, therefore, inter-ested primarily in the radiation exposure ofindividuals from the time of conception to theage of 30, because by the age of 30, we havemade half of our contribution to the nextgeneration. By the age of 40, we have made90 percent of our contribution to the nextgeneration. The effect of radiation damage on


genetic material is different than the effect ofradiation damage on ordinary cell material.When genetic material is damaged, a patternis damaged. Once a pattern is damaged, itremains damaged. Thus, it is possible thatgenetic material damaged by a radiation ex-posure in a person's early childhood may haveits effect in a child conceived by this personmany years later. However, we must also bearin mind the fact that the only radiation ex-posura which is genetically significant is thatwhich strikes the reproductive organs. Radia-tion exposure of other organs or other partsof the body has no genetic effect whatsoever.

Permissible Rate of Exposure

With all the foregoing taken into account,

the supplement to Bureau of Standards Hand-book #59 sets the permissible rate of radiationexposure to industrial employees at an averageof 5 rem per year for each year after the age of18. This is illustrated in figure 7. Note thatthe effect is to keep down not only the totalamount of radiation exposure permitted to anindividual in his lifetime but to keep down therate at which it accumulates, so that his exposuredoes not exceed 60 rem at the age of 30 and 110rem at the age of 40.

A roentgen measures penetrating externalradiation only, in the air. The rem is a meas-ure of the effect of radiation in the body andis used for all types of radiation. At thispoint all we need to know is that one roentgenof exposure to penetrating external radiationequals one rem of effect in the body.

EXPOSURE BANK/NG CHART (VD/AT/ON WORKERS)

250-

t 200-k

'4 150-%

J 5O-

WORKER BANKSSREM A YEAR FOR EACHYEAR AFTER 7HE AGE At

10 20 30 40 5018 AGE IN YEARS

FIGURE 7

24

60


An individual can receive radiation exposurein any given year up to 12 rem.

The easiest working concept to consider isthat the man has a radiation bank account.Into his account 5 rem are deposited per yearfor each year after age 18. He can draw onthis at the rate of 12 rem per year. If he over-draws his account slightly, no particular harm

is done, but in order to keep down his expo-sure, he is restricted until, by the passage oftime, his exposure is down to, or below, thepermitted line.

Let us consider a man who enters radiationwork at the age of 23. Five years have passedsince his 18th birthday.

Please note carefully that this illustration is

5 year x.5 rem per year =25 rem in bank.1st year of work, used 12 rem used.

Added to bank by passage of 1 year

18 rem balance, end lat year.2d year of work, used 12 rem used.

Added to bank by passage of 1 year

3d year of work, used

Added to bank by passage of 1 year +5

6 rem balance, end 3 year.4th year of work used 12 rem used.

6Added to bank by passage of 1 year +5

1 balance, end 4th year (overdrawn).Exposure during 5th year. 4 rem.

5Added to bank by passage of 1 year +5

13+5 rem

6+ 5 rem.

11 rem balance, end 2d year.10 rem used.

1

used just to demonstrate the working of theradiation banking concept. The average an-nual exposure of all monitored employees inAEC plants is less than Moth rem per year,and the 9-year average of the highest annualexposure from all plants is 5.1 rem.

In any regulations, specific numbers must beused, and an individual may feel that he hasbeen injured if the specific number cited hasbeen exceeded to any degree at all. The pur-pose of the regulation is to keep down the

2 r

0 rem balance.

radiation exposure of everyone, including thatportion of the population engaged in atomic:energy work. The fact that a given individualon a given occasion gets a dose slightly inexcess of the figure given by the regulationsshould not be a cause of concern to the in-dividual. He has not been injured, but, ofcourse, it is of serious concern to see that thecircumstances which brought about this tech-nical overexposure are changed so that thesituation will not continue into the future.


The situation is somewhat similar to speedlimits on the highway. We all know thatfrom the practical point of view there is noreal safety difference between driving at 62

- or 60 miles per hour. Yet, when the speedlimit, is posted at 60, the police officer is doinghis duty when he arrests us for exceeding thelimit by any margin, no matter how small.The point is that in regulating any activity,we must state specific numbers in order tohave a definite point of reference. The effectof exceeding the limit slightly, however, israrely of practical significance.

It is particularly important that we under-stand this in radiation work because, for ad-ministrative purposes, the permissible amountof radiation exposure is broken down intoquarterly and weekly periods of exposure.Sometimes there is a feeling that if a man hasreceived his weekly permissible exposure, heis literally standing on the brink of disaster,and any further exposure to radiation maycause him severe harm. For instance, concernhas been expressed over the possibility of anemployee who had received his weekly per-missible dose being involved in an automobileaccident. The supposition was that by addingX-ray exposure to the permitted exposure, "thedoctor would be unwittingly guilty of homi-cide." Nothing could be further from thetruth.

The very intensive efforts made by radiationsafety personnel to keep down radiation ex-posure may bring about a wrong conclusionin the minds of the employees. The 12 remper year is broken down into 3 rem per quar-ter. Under the regulations, it is permissiblefor the employee to get his 3 rem in anymanner during the quarter. That is to say,he may get a single short exposure whichamounts to 3 rem (3,000 millirems), or, as ismore generally the case, particularly whenwork is going on with radioactive materialsconstantly, the 3,000 millirems may be dividedup among the 13 weeks in the quarter. Thus,for instance, a limit of 100, 200 or 250 milli-rems per week may be administratively set, in

order to keep down the radiation exposure ofthe individual so that he does not exceed the3 rem per quarter.

For this reason, if an employee should ex-ceed the administratively set permissible ex-posure, there may be quite an investigation ofexactly how this came about. The reason forthe investigation is not necessarily because spe-cific injury has been done to the employee butthe fact that exceeding the level indicates thatsome unplanned radiation exposure occurred.The concern is not so much with the specificincident which occurred but the fact that suchan incident indicates a possible breakdown inprocedure which might cause trouble if allonredto continue.

Detailed regulations for permissible radia-tion exposures in AEC contractor activitiesare found in the AEC Manual. Regulationsfor licensee exposures are found in Title 10,Part 20 of the Code of Federal Regulations.

It should be further noticed that the Na-tional Committee on Radiation ProtectionRecommendations, contained in Bureau ofStandards Handbook 59, permit a single, once-in-a-lifetime 25-rem emergency exposure with-out effect on the 5-rem per year exposure rate.Medical and dental Xlray procedures weretaken into account when the regulations wereset. The regulations also permit higher ex-posure levels to the hands than to the bodyas a whole.

We see, therefore, that the radiation expo-sure figures have been set far below the levelat which an injury can occur in any specificexposure situation. They are set up at thislow level to reduce the cumulative effect of theradiation exposure, primarily because of thepossible genetic effect of exposure up to theage of 40; secondarily, because of possibleeffects on the individual as a result of con-tinual low level exposure to radiation.

The levels have been set in the light of ourbest available knowledge, as have other per-missible exposure levels, such as for carbontetrachloride, carbon monoxide, or other in-dustrial poisons. Further research may tell us


that radiation levels presently permitted shouldbe reduced because of various factors not yetdiscovered. On the other hand, it is possiblethat further research may permit a relaxationof the rule.

Regardless of the numerical values of radia-

tion exposure permitted, the mean of protec-tion against radiation hazards will not change.The degree to which we apply the means ofprotection will, of course, vary, dependingupon the level of radiation exposure we intendto permit.

Chapter V

PROTECTION FROM EXTERNAL RADIATION

The means of protection from external radi-ation exposure are a combination of threethings : distance, shielding.

That is to say, protection is provided by:1. Controlling the length of time of ex-

posure.2. Controlling the distance between the man

and the source of the radiation.3. Placing an absorbing material between

the man and the source of the radiation.We cannot use just one of the factors of

protection. The factor of time is always in-volved, but we may have time in combinationwith distance, shielding, or both. In orderto understand each of these factors, we willdiscuss them separately.

Time

The effect of time on radiation exposure iseasy to understand. If we are in an areawhere the radiation level from penetratingexternal radiation is 100 milliroentgens perhour, then in 1 hour we would get 100 milli -rems of exposure. If we stayed 2 hours wewould get 200 millirems; if we stayed 4 hourswe would get 400 millirems; and if we stayed8 hours we would get 800 millirems of expo-sure, as shown in figure 8.

Time is used as a safety factor by keepingthe time of exposure down to the absoluteminimum. For instance, if work must be donein a high radiation area, tile work to be doneshould be carefully preplanned outside thehazard area so that the minimum time is usedwithin the radiation area to accomplish thework.

Time is also used sometimes for administra-tive regulation. Consider a situation wherethere is but a single radiation source in a

plant. This source is in a room in which theradiation level is about 20 mr per hour. Wedon't want anyone to get more than 100 mrper week. If we wish our employees to beable to go into the room in which this radia-tion source is located on each of the 5 days oftheir work week, we would divide up the 100mr per week by 5 days and arrive at an ad-ministrative permissible dose of 20 mr per day.

Since the rate is 20 mr per hour, we wouldthen post a sign that no employee was to re-main in this room more than 1 hour in anyday. By this means, we would anticipatethat his radiation exposure would not exceedthe limit set for this operation. By the useof film badges, or dosimeters, which will bediscussed later, we would check his actualradiation exposure.

Time is also useful to us in other problems.In an accident on the highway, for instance,a relatively high radiation area may be createdbecause a high intensity source of penetratingexternal radiation is stripped of its shieldingas a result of the accident.

On the opposite side of a wide highway,such as a turnpike, there might be a radiationlevel quite high when considered in terms ofpermissible radiation level in industrial plants.Assume that the radiation level on the op-posite side of the highway from the accident,is 5 R per hour. This is a very high radiationlevel when considered in terms of normal in-dustrial exposures. However, assume that itwould take a person riding in a car only 10seconds to get through the radiation area.There are 3,600 seconds in an hour. There-fore, the person driving through the areawould receive only %Nth of the 5 r per hour(5,000' milliroentgens per hour) rate. Theactual dose to a person passing through that

2

23


1 hour 100mr

4hours 400mr

8 hours 800mr

FIGURE 8

area and remaining only 10 seconds would beabout 14 mr, an inconsequential dose of radi-ation.

Distance

The effective of distance on radiation expo-sure is quite startling. This effect is dueto the inverse square law. That is to say, theintensity of radiation falls off by the square ofthe distance from the source. Figure 9 showsit very simply.

If we had a point source of radiation givingus 1,000 units of penetrating external radia-tion at 1 foot, we would receive only 250 unitsat 2 feet because we have doubled the distance,and the effect on the radiation level is to re-duce it to (I/2)2 or 1/4. When we have tripledthe distance, we have reduced the dose to (%)2or %th, to 111 units and so on. At 10 feet

On Radiation

Exposure

away, we have No ) 2 or %00th of the radiationexposure at 1 foot, i.e., 10 units.

We should explain that the inverse squarelaw applies to the degree that distances arelarge in relation to the size of the source.Radiation sources used in industry for pene-trating radiation are generally quite small insize, so the inverse square law can be appliedto distance in the immediate vicinity of thesource. If, however, the source is large insize, such as the side of a reactor, which coversa considerable area, or as might be the caseif the radioactive material were dispersed,then the inverse square law does not start toapply until the distances are large in relationto the size of the source.

Let us look at our chart now in terms ofactual doses and their possible effect on a man.Consider that the radiation rate at 1 foot is1,000 r per hour and a man remains at that

id

1

ti

Protection from External Radiation 25

FIGURE 9

distance for 1 hour. He will receive 1,000 rem,an absolutely lethal .dose of radiation.

If he remains 2 feet from the source for1 hour, he will receive 250 rem. This putshim on the threshold of dying and he mightbe extremely ill. At 3 feet, he would receiveonly 111 rem, and we would not expect that hewould die, but he might be quite sick for aperiod of time.

At. 4 feet, he is already in a range wherethere would probably be no symptoms that hewould detect, and the only damage that wecould find would be certain changes in hisblood which would reverse themselves with thepassage of time. If we extended our chartout to 20 feet, we would see that the manwould get only 21/2 rem, this is 1 /400th (Y20) 2 ofthe dose at 1 foot, less than the amount per-mitted to a radiation worker in a 3-monthperiod.

We see, therefore, that there is a dramaticfall-off in the rate of radiation exposure aswe go away from the source of the radiation,and a very little bit of distance can gl a longway in increasing our safety factor.

Conversely, as we close in on the radiationsource, our levels will go higher by the samemathematical process. For instance, if we movein to 6 inches, the radiation rate will go from1,000 r per hour to 4,000 r per hour. Thishelps to make us realize one of the most funda-mental rules of radiation protection, which isto maintain the maximum possible distance be-tween ourselves and the source of the radiation.We should avoid touching materials whichgive off significant amounts of penetratingexternal radiation because ir such a case wehave obviously no distance at all workingfor us.


FIGURE 10

Shielding

You will recall, that we said that the damag-ing effects of radiation comes from the factthat the rays strike electrons in the body andknock them out of their orbit, and if thishappens to sufficient electrons in the body, wehave received radiation damage. If we wishto stop a high proportion of the rays beforethey get to us, we can place between ourselvesand the source of the radiation a materialwhich has a lot of electrons in its makeup.The more electrons there. are in the makeupof the material the more of the radiation willbe stopped.

Figure 10 shows lead and water in a roughcomparison of their atomic makeup. Noticethat lead has a lot more electrons in theorbits of each atom than does water. There-fore, lead makes a better shield than water.

.31

Figure 12 shows the relative efficiency ofvarious shielding materials. Lead, iron, con-crete, and water, are efficient in about the pro-portions shown on the chart in stopping thesame amount of radiation: Various shieldingmaterials are used in various applications, de-pending upon the purpose to be served. Lead,for instance, is quite compact and is most suit-able where space requirements are a factor.On the other hand, water is used where it isnecessary to see through the shielding mate-rial and to work through it with a long-handled tool to perform necessary operations,such as, sawing or cutting the radioactivematerials.

When we consider that matter is mostlyempty space, we realize that no material canbe an absolute barrier to radiation. Regard-less of the thickness of the material, we cansee how some radiation can get through the


RADIA7701/LEVEL

25,600mr/h

8 77MES

1204800

noth

TYPICAL EFFECT OF ADDING SUCCESSIVEHALF VALUE LAYERS OFSHIELDING

3 4

12,800 6,400 3,200 1,600 800mr/h mr/h mr/h mr/h m0

102,900 .57,200 25,600 /2,800 6,900in,/h in0 IPA InVh

2 3 4 6

7 X = 3A"LEAD

400 200nYVh nVh APPROX. .172 TIMES

13,200 4 600 800 400 200mr/h miyh ngh mVh mg/h

7 8 9 10 X pz"= SHLEAD

V2 "LEAD MEETS (HALF VALUE LAYERFOR 2 AfEi! GAMMA RADIATION)

FIGURE 11

material without hitting any electrons and,therefore, without being absorbed.

Half Value Layer

In calculating shielding for external radia-tion exposure, the amount of shielding it willtake to stop all of the radiation is not a usefultype of measurement, since there is no amountof shielding that we can say will stop all ofthe radiation. The measure that is used is thatamount of shielding that it takes to stop halfof the amount of radiation of a given in-tensity. This is the so-called half-value layer.

Examine figure 11. At the left-hand sidewe show two sources of radiation, one givingoff 25,600 mr/hrthe other giving off 204,800mr/hr. The larger soured has 8 times thestrength of the smaller source. As we addsuccessive half-value layers of shielding, thestrength of the radiation emerging from theother side of the shielding is cut in half. Ittakes 7 half-value layers of shielding to reach200 mr/hr in the case of the source emitting25,600 mr/hr. It takes ten half-value layersto reduce the larger source to the same 200

mr/hr. Although the larger source has 8 timesthe strength of the smaller source, it takes onlyapproximately 11/2 times as much lead to re-duce the radiation level emerging from theoutside of the shielding to 200 mr/hr.

This demonstrates that the thickness of radi-ation shielding does not have to increase indirect proportion to the amount of radiationbeing shielded. A container, for, instance, fora 1,000-curie radiation source does not haveto be a 1,000 times as heavy as one for a 1-curie source. As a matter of fact, the con-tainer for a 1,000-curie radiation source isabout 13 times as heavy as a container for a1-curie radiation source.

This also helps us to understand that a state-ment such as "radiation can penetrate 22 inchesof lead" of itself means nothing, because radi-ation can penetrate an indefinite quantity ofmaterial. The important question is, "Whatamount of radiation escapes from the far sideof the shielding ?" the point at which theradiation can become effective en human beings.

The technician in the radiation protectionfield has at his disposal tables of half-valuelayers for various materials for various in-tensities of radiation, and these are used in


CONCRETE

IRON

WATER

FIGUBE 12

the construction of radiation shielding. Afterthe shielding is placed, tests are made to besure that everything is shielded to the extentshown in the calculation.

Curies

The amount of a radioactive material whichis present is expressed in curies, or millieurie8,or mierocuries. A millicurie is a thousandthof a curie and a microcurie is a millionth of acurie. A curie is that amount of radioactivematerial which is disintegrating at the rate of37 billion atoms per second. The curie bearsno relationship to the weight of the materialinvolved. If a material is very slightly radio-active, several thousand pounds might be re-quired to give one curie of radioactivity. Ifa material is very highly radioactive, a frac-tion of an ounce of the material might be acurie. See Appendix B.

For instance, one curie of cobalt 60 wouldweigh appr'ximately 880 micrograms, while

one curie of thorium 232 would weigh 10 tons.The curie is not a measure of the radiation

hazard from the material because the curiesimply tells us that so many disintegrationsare taking place every second. The problemis, "What happens when an atom of this par-ticular material disintegrates?" The hazarddepends upon the quantity and type of radia-tion emitted.

When an atom of radioactive cobalt 60 dis-integrates, two penetrating external rays artgiven off from each disintegration. When anatom of radioactive iron disintegrates, onlyone ray is given off.

When we are measuring roentgens, we aremeasuring these rays, and, therefore, from acurie of cobalt disintegrating, we will get twiceas many rays as we will get from a curie ofiron. Therefore, we will measure approxi-mately twice as many roentgens.

As we will see later, a curie of some mate-rials might not give us any roentgens at all,because these particular materials do not give


off penetrating external radiation when theydisintegrate. So, we have no measure of theproblem of dealing with the material until weare told not only how many curies or milli-curies are involved but what the specific ma-terial is, just as we would have no measureof the hazard if somebody said, "I have in mybasement a gallon of a flammable hydrocar-bon," as this might be gasoline or it might beheavy fuel oil.

Cobalt is one of the most widely used radio-isotopes; for this reason, we will work someproblems in terms of cobalt.

A curie of cobalt gives off 1.6 roentgens perhour (1600 mr/hr) at a 8-foot distance. At a9-foot distance, we have tripled the distance, sothe radiation exposure is one 1/2th s much, orabout 176 milliroentgens per hour. At a15-foot distance, the distance is multiplied by5, so our radiation level is 1 /25th of what it wasat the 3-foot distance. Therefore, we are downto 63 milliroentgens per hour. Observe thefollowing problems :

A man remains 6 feet from a 10 curie cobaltsource for 2 hours. What is iris approximateradiation exposure?10 curie cobalt 60 source=16 r per hour at 3 feet

4 r per haY:r at 6 feet(14)

4 r per hour x 2 hours=8 rem

Man receives 8 rem exposure.

A man remains one-half hour at a distance of9 feet from a 500 millicurie cobalt source, whatis his approximate radiation exposure?500 me cobalt 60=1/2 curie1 curie cobalt 60=1.6 r per hour at 3 feet% curie cobalt 60=.8 r per hour at 3 feet% curie cobalt 60=.09 r per hour at 9 feet (1/2)% hour exposure=.045 rem or 45 milirems

A man remain 11/2 feet from a 10 curie cobalt60 source for 2 hours. What is his pproximateradiation exposure?10 curie cobalt 60 source=16 r per hour at 3 feet

64 r per hour at 11/2 feet64 r per hour x 2 hours

=128 rem

Man receives 128 rem exposure.

Because of an accident, a 500-curie cobalt 60source has been completely unshielded on ahighway. This highway is a dual lane turnpiketype of highway, with an approximately 90-foot strip in the middle between the two road-ways. What will be the highest radiation read-ing on the opposite roadway ?500-curie cobalt 60 source= 800 r per hour at 3 feet

90 feet is 30 times 3 feetRadiation level is 1/2021/200 of 800 r per hour

=.9 r per hour

Short Range External Radiation

We have been talking, thus far, about long-range penetrating external radiation. Thereis another type of radiation hazard which is lesspenetrating and has a shorter range. This typeof radiation represent an external hazard onlywhen we come in extremely close contact withthe radioactive materials, as by handling orallowing the material to be deposited on ourbodies and not promptly washing it off.

As we note in figure 13, we cannot tell whichone of the 45 caliber automatics is loaded, andtherefore, dangerous, and which is not, for bothlook alike. The same condition prevails withradioactive materials. Some radioactive ma-terials are quite safe to handle with the barehands ; others are notand it is impossible totell by looking at the material whether it is safeto handle it with the bare hands. The generalrule is very simple : Don't handle radioactivematerials with your hands unless you know thatit is safe to do so.

How Things Don't Get Radioactive

There is a widely believed misconceptionthat radiation from radioactive materials canmake other things radioactive. Some peoplebelieve that a person who works with radio-active materials will become radioactive. Ifa radiation source is left on a desk or table,and the source is removed, they believe that


One is dangerous...One is not...

YOU CAN'T TELL

'I II I I....I

I

FIGURE 13

a radioactive area is left on the surface of thetable. If a radiation source is involved ina fire, and smoke and water pass through theradiation field, it is widely believed that thesmoke and water will thereby become radio-active. Figure 14 illustrates this question.(We are not here considering the picking upof some of the radioactive material by thesmoke or water.)

Think back a moment to the structure ofthe atom and the effect of the radiation fromradioactive material. The radiation strikes theelectron, knocking the electrons out of orbit.To make something radioactive, we must pene-trate the nucleus of the atom because radio-activity originates in the nucleus. The raysfrom radioactive materials do not significantlypenetrate the nucleus, and, therefore, cannotmake something radioactive.

a

We will learn later on how materials do getradioactive, but let us be sure that we under-stand that materials do not get radioactive bybeing exposed to other radioactive materials.The material has been "irradiated," and ifsufficient radiation has been applied to knockout a substantial number of electrons, theremay be an observable chemical effect in thematerial which has been irradiated, but thematerial has not been made radioactive.

Nomenclature

Up to this point, we have been talking aboutpenetrating external radiation, less-penetratingexternal radiation, and nonpenetrating radia-tion. It is time now that we provide names.

The most penetrating type of radiation iscalled gamma radiation. This radiation is

Protection from External Radiation Hazards 31

I

k_

FIGURE 14

similar to X-rays, and it comes in the form ofelectromagnetic waves which have only energyand no substance at

The less-penetrating type of external radia-tion is called beta radiation. This is reallya high-speed electron ejected from the nucleus.Sometimes we read of beta rays or beta par-ticles. We are speaking about the same thing.Beta radiation has a relatively short range inthe air, in general not more than a few feet.

Alpha. radiation is the nonpenetrating ex-ternal radiation. The alpha particle is a pieceof the nucleus of the atom. It cannot pene-trate the dead outer layer of the skin, and,therefore, the alpha radiation represents noexternal hazard at all.

In general, a radioactive material will. emiteither alpha radiation or beta and gamma

%

e

radiation from the disintegration of any atom.For reasons which we will show later, all threetypes of radiation may be coming from aparticular material.

External Versus Internal Hazard

We will now classify the radiations as torelative internal and external hazard.

Alpha radiation represents practically noexternal hazard since it cannot penetrate thedead outer layer of the skin. However, whena material which emits alpha radiation getsinside the body, the energy from these piecesof the nucleus is all taken up very close tothe location where the radioactive material isdeposited in the body, and there is no deadlayer of skin to protect the living tissue of the

36


body. Therefore, alpha radiation emittersrepresent the worst internal hazard.

We have seen that beta radiation is relativelyshort-range, and the external hazard is a prob-lem only when we are quite close to it. There-fore, if we get a material emitting beta radia-tion fixed in the body, it can do damage insidethe body within a relatively localized areaaround the site of the material in the body,as does alpha radiation.

Gamma radiation, of course, represents themost severe external hazard because of thelong-range and high penetration of the gammarays. When a gamma emitter is depositedinside the body, its energy will be diffusedthrough a, larger area of the body, and alsosome of the rays will pass right out of thebody without ever touching any of the electronsin the body.

Very often the question is asked, "Whichtype of radiation is the most hazardous?"This is rather like asking, "Which is morehazardousa fall or a burn?" Probably thesimplest answer is whichever does the mostdamage in a given set of circumstance's.

Roentgen, Rad, Rem, RBE

In order to provide a means for comparingthe radiation effect of different types of radia-tion, a number of terms have been developedand standardized. These terms include roent-gen, rad, rem, and RBE.

The roentgen measures only X or gammaradiation in the air.

The rad measures the absorbed dose of anytype of radiation. A rad of one type of radia-

tion may have more effect on the body thana rad of another type.

This is expressed by the RBE (relative bio-logical effectiveness). For instance, the RBEof gamma radiation is 1. The RBE of somealpha radiation is 20. This means that 1 radof alpha radiation can have approximately20 times the effect in the body as 1 rad ofgamma radiation.

The rem is the unit of radiation dose whichmakes it possible to express radiation expo-sures of all types in one term.

Type of radiationDose inrads ;,'SE

Dose inrems

Gamma 1 X 1 = 1

Beta (1.0 MeV.) 1 X 1 = 1

Alpha (1 MeV.) 1 X 20 = 20

The external radiation hazard is really oneof the easiest industrial hazards to control be-cause we have instrumewts which can measurethe hazard at the time the hazard exists. Wehave devices, such as filrr. badges, and dosime-ters, which will measure the exposure to per-sonnel. I f an exposure occurs without instru-mentation or measuring devices being presentat the time of the exposure, we can reconstructthe approxiMate exposure based upon time anddistance from the source. The effects of seri-ous external radiation exposures show up rela-tively rapidly so that we generally know soonafter the incident whether there is any prob-lem of injury to the individual or not.

Having completed our discussion of externalradiation hazards, we will now proceed to theproblem of internal radiation hazards.

r,"!,,,7,Y2tV:rrNT,:rA7vIllromutro

Chapter VI

INTERNAL RADIATION PROBLEMS

By contrast with the external radiation ex-posure problem, the internal radiation exposureproblem is a much more complicated one.Many factors are involved. There are fourpossible ways to get radioactive materials intothe body :

1. By breathing.2. By swallowing.3. Through breaks in the skin.4. By absorption through the skin.When a radioactive material gets into the

body, the first question is "How long does itstay in the body"? A high percentage of any-thing we inhale is immediately exhaled. Ma-terials which we swallow which are not solublein the body's digestive system are dischargedrapidly through the feces. If a material issoluble and is breathed into the body, it willgo to the blood stream. The blood streamthen carries it around the body to the variousorgans, in effect offering the material to theorgans.

The body is a chemical machine, and, there-fore, the organ looks at the substance chem-ically. If the Organ rejects the substancechemically, the blood stream takes it alongtrying to give it away. If no organ will acceptthe material, the blood takes it to the kidneys,and the kidneys dispose of the material throughthe urinary system. If, on the other hand,the organ has a use for the material, or if theorgan thinks the substance looks like a mate-rial it can use, it accepts the substance. Forinstance, the bones need calcium; radium chem-ically looks like calcium. Therefore, when theblood takes radium to those areas where thebone is building new bone tissue, the boneaccepts the radium. Thus, the radioactive ma-terial is deposited in the bone.

Some chemical substances, such as sodiumand potassium, are widely used throughoutthe body, and, therefore, if a radioactive formof one of these elements is introduced into thebody, it will be dispersed throughout the en-tire body. Other elements tend to concentratein speCific organs, as iodine does in the thyroidgland. The point to remember is that bodyorgans react to a 1.,ubstance on the basis of itschemical nature only, without regard towhether or not the material is radioactive.

Some organs are much less "critical" to thebody than others. For instance, we could notpossibly live if our kidneys were removed,whereas the removal of the spleen is not nearlyso critical because other organs of the lym-phatic system will pick up the work load ofthe spleen.

The radioactive half-life of the material isimportant. We will discuss half-life morefully later. Briefly, the half-life is that amountof time that it. takes ball of the material tolose its radioactivity. If a material has aradioactive half-life measured in fractions ofa minute, for instance, it will be dissipatedVery rapidly. On the other hand, if the ma-terial has an extremely long half-life, possiblymeasured in the thousands of years, then therate at which it. is decaying is very slow. Weare only interested in that radiation effect thattakes place while we are still alive. Radiationbeing given off in our skeletons after we dieis of no interest to us. For this reason, ingeneral, materials with radioactive half-livesfrom 5 to 40 years are the most significantfrom the point of view of half-life.

The biological half-life of a material is thatperiod of time which it takes for half of thematerial to be excreted from the body. Some

'48

33


materials are excreted quite rapidly from thebody, and, therefore, will not be in it longenough to do much harm.. When we combinethe radiological half-life with the biologicalhalf-life, we have the effective half-life of thematerial in the body.

There is a sizable amount of medical infor-mation available on the effect of radioactivematerials in the body, although, of course,much research remains to be done. Many ofus are familiar with the classic cases in thefield of radiation poisoning. These are thecases of the women in the radium dial paintingplant in New Jersey, who pointed up thecamel's hair brushes with their lips, and thusintroduced radium into their bodies over along period of time.

As a result of much work in this area, stand-

ards have been arrived at for the permissiblebody burden of various radioactive isotopes inthe body similar to the permissible levels ofradiation exposure from external radiation haz-ards. Working backward from the permissiblebody levels, permissible air concentrations ofthe materials were arrived at, because it isprimarily by means of breathing and swallow-ing that the radioactive materials can get intothe body on a continuous basis. These levelsare stated in terms of microcuries per milliliterof air.

The hazard of absorption through the skin,where it exists, is handled by the provisionof suitable protective clothing or gloves. Theintroduction of radioactive material throughwounds is avoided by standard safety tech-niques to prevent injury.

39

4TrirtTreanaMe.crr,-.ms

Chapter VII

PROTECTION FROM INTERNAL RADIATION HAZARDS

In the handling of radioactive materials, itis possible that certain processes will permitthe material to become airborne where it canbe breathed by personnel. It is necessaryunder such circumstances that varying degreesof control precautions be taken. The simplestsituation might require merely the applicationof ordinary hygienic procedures. The worstsituation might require that the entire process-ing equipment be totally enclosed in order toprevent any material from escaping into theworking atmosphere.

To determine whether or not the airborneconcentration of the radioactive material isbelow the permissible standard, it is necessaryto take a sample of the air which is breathedby the employees. Air samplers are nothingmore than air pumps which pull a measuredquantity of air through a filter paper whichstrains out all of the material in the air. Thefilter paper is then sent to the laboratory foranalysis, and determination is made as towhether the air concentration is below the per-missible level.

If the air concentration is found to be abovethe permissible level, an investigation must bemade to find out why the concentration isabove the permissible level. Has the procedurebeen changed since it was first set up? Is theventilating system functioning properly? Arethe containers being handled in the propermanner? These are some of the questionswhich might be gone into to find the reasonfor the excessive concentration.

We must, of course, bear in mind the factthat, with some except tons, the hazard of get-ting radioactive materials into the body is achronic hazard, that is to say, that in manycases it would be impossible in a single inci-dent, or in a short space of time, to breathe

in sufficient amounts of the material to con-stitute an appreciable portion of the permissi-ble body burden.

In most cases, the problem is one of main-taining good techniques over an extendedperiod of time and insuring careful complianceby all employees with all regulations, eventhough the violation of a regulation in a singleinstance might not, of itself, be extremely seri-ous. For instance, smoking is often forbiddenin the areas where radioactive materials arehandled because of the obvious ease of trans-ferring material from hand to cigarette tomouth and, thus, into the body. Eating isgenerally prohibited in the area for the samereason. In some cases, special work clothesare provided which are washed and remainat the plant. Sometimes it is necessary thatthe employees take a full shower and changeclothes before they leave for home or even goto the lunchroom. In each case, the degree ofprecaution is based upon the nature of the haz-ard of the specific material being handled. Noparallel can be drawn between the precautionstaken in one plant and the precautions takenin another, unless we know fully the natureof the material handled and the airborneconcentrations of the materials present in eachof these plants.

In general, therefore, the approach to thesafe handling of radioactive materials whichmay present an airborne radiation hazard isto confine and contain the materials at all timesso as to prevent their becoming airborne. Alltechniques are devoted to this end. Materialsare handled in closed systems, vacuum cleanersconnected to a permanent system are used topick up dust rather than brooms, ventilatingsystems are carefully engineered to provideair flows in the proper direction and amount,

40

35


INTERNAL RADIATION IS RECEIVED

Apt:flg-

°t Radioactive Materials.

THERE ARE SEVERAL PRECAUTIONS

FIGURE 15

etc. Where personnel may be exposed to air-borne concentrations unavoidably, then respira-tory protection can be used. This may rangeanywhere from the relatively simple filter typeof respirator, up through filter type gas masks,to self-contained gas mask equipment, and on

EXHAUST SYSTEMS MUST BE OPERATEDAS DESIGNED

SOOD DESIREE El INSTALLATION CAN SE RUINEDBY POOR OPERATION OR MAINTENANCE

cove RCONTAINERSOF' 01"MATERIAL

WHEN BEINGHANDLEDOR MOVED.

to a completely enclosed plastic suit with anindependent air supply from the outside of thebuilding.

Figures 15 and 16 are taken from the "Radi-ation Safety Primer," a publication preparedby this office and available from the Superin-

j

Protection from Internal Radiation Hazards 37

tendent of Documents at 2q. A set of colorslides and Instruction Handbook are also avail-able. Write this office for details.

KEEP YOUR HANDS OUT 4;:c"HOT" MATER I#L.

WASH UP I3EYORE YOU EATAND BEFORE YOU GO tiOME.

If personnel have been exposed to possiblyexcessive concentrations of airborne radioactivematerials, it is then necessary to attempt to

BROOMS STIR UP DUSTUSE

VACUUMCLEANERS

DO NOT EAT IN AN AREAWHERE RADIOACTIVE MATERIALSARE PROCESSED.

FIGURE 16

42

WHETHER YOU BRING IT OR BUY IT.

exmortovammifttrnir :


determine how much of the radioactive mate-rial the man has gotten into his body. Theseso-called bio-assay techniques are, in somebases, costly, time consuming, and not veryaccurate. They may include the analysis ofbreath samples, stool samples, urine samples,blood samples, bone marrow samples, etc.

What can be dime for a man who has re-ceived an excessive concentration of a radio-active material in the body of a type whichwill not correct itself by the natural processesof elimination but tends to remain in somecritical organ of the body I Various methodsare being studied to accelerate the removalof the material from the body. At this writ-ing, these are of limited value.

If your work brings you into contact withairborne radioactive materials, it is necessarythat you comply strictly with all of the safetyprecautions which are laid down. Under nocircumstances should procedures be violated orshort cuts be taken on the basis that one ortwo exposures won't hurt anybody. Whilethis may literally be true, the effect of such

43

a disregard of such regulations over the longrun may prove extremely injurious.

In an emergency situation, particularlywhen the ventilating system or containmentsystem has been disrupted, there is no readilyavailable procedure for making an immediateanalysis of the airborne radiation hazard. Theonly overall answer is that all personnel whomust enter the area should wear masks witha self-contained air supply to protect themagainst breathing or swallowing any radio-active material. In such a mask, the weareris completely cut off from the atmosphere sur-rounding him. In a filter type of mask, theman breathes the surrounding air through afilter. Certain filter masks are quite satisfac-tory for use in certain situations. Upon leav-ing the emergency area, such personnel shouldimmediately shower and change clothing toremove any remaining radioactive material.These precautions will provide real assurancethat the personnel have received no depositionof radioactive materials in. their bodies.

Chapter VIII

CONTAMINATION

Where radioactive materials which can beeasily spread around are handled, all personnelmust be alert to the possibility of the spreadof radioactive contamination. Like all otherradiation problems, the situation may be rela-tively minor or extremely severe, dependingupon the nature of the material, the type ofradiation given off, and requirements for useof the area. For instance, in a laboratorydoing very precise radiation measurements, avery small amount of radioactivity insufficientto represent any danger to health may inter-fere seriously with the work being performedbecause the background level in the laboratoryis increased by the contamination. At theother end of the scale, it is possible to con-taminate a building so severely that it ischeaper to abandon the building than to at-tempt to decontaminate it.

The hazards from radioactive contaminationmay be from alpha, beta, or gamma radiation.If an alpha emitter is deposited on a surface,such as a wall or floor, this, in itself, wouldrepresent no problem, since the short rangeof the alpha radiation does not permit it toreach anybody and do him any harm. How-ever, alpha-emitting contaminants on a surfacemust be dealt with because there is always thepossibility that they will become airborne andthereby breathed by the people in the area.

Beta emitters present both the possibilityof becoming airborne and creating high radia-tion levels near the surface of the contaminatedarea.

If the contaminant is a gamma emitter, thena high radiation area may be set up in theentire contaminated area due to the gamma rayscoming off of the tiny bits of radioactive ma-terials which are spread all around the area.

Of course, materials emitting all three typesof radiation may be present.

Prevention of the spread of contaminationtakes many forms. Procedures for the controlof materials, covering of containers, enclosureof processes, etc., should be complied with care-fully. Clothing which is restricted to one areashould not be worn when passing from a con-taminated area to a clean area. In manyplants, this is enforced by marking clothingto be worn only in a contaminated area by suchdevices as a red collar, or by other means.Personnel working with radioactive materialswho might get hands or feet contaminatedshould not leave the contaminated area for aclean area without first checking at a handand foot counter, or other monitoring device.A hand and foot counter is a device whichautomatically registers the radioactive con-tamination on the hands and feet. If the read-ings are above the permissible backgroundlevel, the person should not leave the areawithout cleaning up.

In areas where contamination may reason-ably be expected to occur, oftentimes specialpreparations are made to make it easy to de-contaminate. Paper tissues are spread on table-,ps and on laboratory benches to gather upthe contamination. Special strippable films areused on wall surfaces so that the paint can beeasily stripped off and replaced when it be-comes contaminated. The design of air con-ditioning systems should be carefully thoughtout to avoid the spread of contaminationthrough the air conditioning system from onearea to another. Contaminated equipmentbeing removed from the plant must also begiven special handling. In some cases, thismaterial is encased in plastic prior to being

44

39

40

...1111INTRPOIMI.IIIMINA

Living With Radiation

,oavvrmatvi; V121" MI.R122,

removed. A special cap is placed on the endof contaminated pipe or the material may bethoroughly decontaminated before removing itfrom the area.

Clean, up

When an area has been contaminated andit is necessary to clean up the situation, thereare a number of possible techniques, depend-ing upon the nature of the problem.

If the contaminant has a short h,alf-life, itis sometimes simpler to allow the area to re-main idle until the radioactivity has died offby the natural process of the passage of suffi-cient half-lives. If we had a reading of 100mr per hour in a room contaminated with a24-hour half-life gamma emitter, in 24 hours

the reading would be down to 50 mr; in an-other 24 hours it would be down to 25 n...rper hour; in another 24 hours it would be downto 121/2 mr per hour, etc. See figure 17.

A useful rule of thumb is the fact that thepassage of 7 half-lives will bring a radiationlevel down to 1 percent of what it is at thepresent time, and in 10 half-lives, the levelwill be down to 0.1 percent.

If the material is an alpha emitter, it canbe fixed to the surface by painting, since thealpha radiation cannot penetrate the paint.Floor tile can be removed and replaced inorder to remove contamination. In general,however, 'contamination is removed by scrub-bing of surface with detergents which are bestsuited to remove the particular material withwhich the surface is contaminated. It is im-

DECAY OF A RADIOACTIVE MITER /AL Wfirli A 24 HR. HALF L/FE

-4-200 rnr/h

100 mr/h

ti

50 mt/h

IN 7 M407./FE PERIODSTHE RADIOACTIVITY DA--THE MATERIAL HAS

DECAYED ro LESS MAN

....... ..........

Itt14tlf214

`,9

24 HR. 24 HR.

.. . .......................

1 2

MR. 24 RR. 24 HR.

6 '7 DAYS

ONENALFLIPEPERIOD

FIGURE 17

Cokamrination 41

possible to "neutralize" radioactivity as wemight think of neutralizing an acid spill withbicarbonate of soda. Radioactive contamina-tion is simply radioactive material some placewhere we do not want it, and the only realsolution to the problem is to pick up the ma-terial and remove it if it will not decay fastenough to suit our purpose.

Contaminatica is most easily spread duringan emergency situation, such as an explosionor a fire. An ordinary rubbish fire in a build-ing will bring about an odor of smoke in Inanypoints in the building far removed from thesource of the fire. When we smell smoke, weare actually smelling tiny bits of ash whichhave reached our nostrils from the fire andwere originally part of the paper which wasignited. Radioactive materials involved in afire can spread very easily due to the air cur-rents set up by the fire. They can also spread

easily if, by some accident, they are intro-duced into the air conditioning system, or ifthey are spilled on the floor so they can betracked around. Personnel working in an areacontaminated during an emergency must beextremely cautious that, in their haste to dealwith the emergency, they do not mice thesituation much worse by transferring contam-ination to the clean areas by means of theirclothing, tools, equipment, etc.

Since it is extremely difficult at the sceneof an emergency to set up adequate monitoringprocedures to make sure that nothing contam-inated leaves the area, it t!s most important thatadequate preplanning be done for possibleemergencies, with radiation contaminationproblems considered realistically. The sametype of preplanning should be carried onwhenever maintenance or repair work is tobe done in a contaminated area.

46

Chapter IX

!NSTRUMENTS AND PERSONNEL DOSIMETRY

We are all familiar with the fact that radia-tion can be detected by instruments designedfor the purpose. To the average person, allsuch instruments are "geiger counters." Ageiger counter is but one of the available typesof radiation detection instruments. It is es-sentially a low-level instrument since the maxi-mum reading available on most geiger countersis 40 or 50 mr per hour. Most geiger counterswill register both gamma and beta radiation.By closing a shield which covers the GM-tube,beta radiation which cannot penetrate theshield is screened out, and only the gammaradiation gets through. Beta radiation is,'therefore, computed by taking the open windowreading (beta and gamma), and then subtract-hy, the closed window reading (gamma only).

Higher levels of beta and gamma radiationare read with an instrument called an ioniza-tion chamber. Ionization chambers for CivilDefense use are designed to read as high as500 r per hour.

A scintillation counter is a very precise radi-ation-measuring instrument which will detectminute quantities of gamma radioactivity.

Since alpha radiation has such a very shortrange in air and little or no penetrating ability,it must be detected on special alpha measuringmeters, and the measuring area of the metermust be brought directly to the contaminatedsurface. When an area has been contaminatedwith a pure alpha emitter, the entire surfacemust be scanned thoroughly, inch by inch, todetect the location of the-contamination. Sincethe alpha radiation hag a very limited range,the contamination level at one point is noindication of what the contamination level maybe at another point nearby.

Alpha radiation contamination levels aregenerally stated in terms of so many disin-

42

tegrations per minute per 100 square centime-ters of surface. Where the surface is irregular,and the flat surface of the instrument cannot bebrought to bear, a piece of cloth or tissue isused to wipe a measured area of the surface.Then this piece of paper is measured to geta figure of the contamination on the surface.

The same wipe technique is used for beta- orgamma-contaminated surfaces to determinehow much of the contamination is removableand how much is fixed to the surface.

All of the radiation detectors are rate ?meters,that is, they measure the rate of radiationbeing received by the instrument at the timeyou read the instrument. If the instrument isremoved from the radiation field, the needlewill, of course, return to background and therewill be no indication of the radiation levels towhich the machine has been subjected.

Developments are rapidly being made inthe field of radiation instrumentation, and ad-vice on the purchase of any radiation detectioninstruments should be obtained from personswho are in a position to keep abreast of thelatest developments. All radiation detectioninstruments, however, require skilled mainte-nance and calibration if they are to serve thepurpose for which they are intended. Themere purchase of an instrument or instruments,of itself, serves little purpose. A completeprogram should be set up designed to insurethat instruments will be in operating condi-tion when needed and will be as accurate asnecessary for the service intended.

Dosimetry

For the protection of individuals, we needdevices which will measure the accumulatedradiation exposure. These come in two typesfilm badges, and pencil dosimeters.

47

Instruments and Personnel Dosimetry 43

Film badges are a bit of dental X-ray filmworn in a special holder. The X-ray film issensitive to radiation in various ranges andwhen developed by standard photographictechniques, the film will be darkened in pro-portion to the amount of radiation received.When the darkening of the film is comparedwith the darkening of similar films which havebeen exposed to a known amount of radiation,the amount of radiation which the film badgehas received is indicated. The film badge willindicate the radiation which the man has re-ceived only if it is always worn when in theradiation area and if it is not exposed toradiation when it is not being worn by theman to whom it is assigned. Film badgesprovide a permanent record of radiation ex-posure, but not an immediate one, because ofthe time required for developing the film andreading the badges.

For a ready available accumulative record

of radiation exposure, a pencil dosimeter isused. A pencil dosimeter is a device whichwill record the radiation which is received,starting from zero, when the device is properlyset, to the limit of the scale of the particulardosimeter. Some dosimeters can be read di-rectly by holding them up to the light; othersmust be read in a reading device provided forthe purpose. Dosimeters can be caused to givefalse high readings by being dropped or dam-aged by electrical leakage, and, therefore, aregenerally worn in pairs.

The primary rule for wearing personnelmeasuring devices is to wear the device pro-vided at all times when in a radiation area andto protect it from radiation exposure when itis not being worn.

Film badges and pencil dosimeters will notrecord alpha radiation, of course. This is ofno consequence since external alpha exposuresare no hazard.

48

Chapter X

A LITTLE RADIATION PHYSICS

We have seen that material does not becomeradioactive by being subjected to alpha, beta,or gamma radiation from a radioactive mate-rial, and that a material does not becomeradioactive when it is contaminated with aradioactive material.

We do know that things can be made radio-active somehow or other, and we. should havesome idea of how this comes about.

In addition, we should have a basic under-standing of the atomic fission process and howthe energy available from the splitting ofatoms can be used to generate electrical power.Furthermore, we should be aware of the prob-lem of the handling of so-called fissionable orcritical materials. Finally, there are some un-answered questions about the decay of radio-active materials. How can we read gammaradiation from a radium dial wrist watch whenradium is a pure alpha radiation emitter?

It is necessary, therefore, that we delve alittle further into the structure of the atomat this point.

Earlier we discussed the nature of matter,and we left the description of the atom atabout the following point. The atom consistsof a heavy, dense, hard nucleus, which containspractically all of its weight, but which is sur-rounded at quite some distance f .om the nu-cleus with a number of electrons which havepractically no weight at all.

It is now necessary for us to examine thestructure of the nucleus in a little greater de-tail. The nucleus consists of little individualballs of matter. all of them about the samesize in all atoms. Some of these little ballsof matter have a positive electrical charge.These are called protons. Others have no elec-trical charges at all; they are electricallyneutral. These are called neutrons.

44

For each positively charged proton in thenucleus, there is a negatively charged electronin the orbit. The number of protons in thenucleus, therefore, determines the number ofelectrons in the orbit. The number of protonsalso determines the nature of the element. Innature, we find elements with the number ofprotons ranging all the way from one proton(hydrogen) to 92 protons (uranium). Eachtime we change the number of protons, wehave an entirely different element.

The number of neutrons in the nucleus mayrange from none to almost 150. In the caseof certain elements, we find that different atomsof the same element have the same numberof protons but have different numbers of neu-trons. To the chemist, these are the sameelement because the chemist really works withthe electrons, and since all of these atoms havethe same number of protons, they will havethe same number of electrons.

Since they have a different number of neu-trons in the nucleus, however, the variousatoms of the same element will not all weighthe same.

To the nuclear physicist, these are differentsubstances of the same chemical form but vary-ing in their atomic weight. These are calledisotopes. Some of the isotopes may be un-stable, and, therefore, radioactive. Some ofthe isotopes may be stable and not radioactive.

The atomic number of a substance is thenumber of protons in the nucleus. The atomicweight of a substance is the sum of the numberof protons and neutrons. Thus, two isotopesof the same substance will have the sameatomic number but will have different atomicweights.

Figure 18 shows various isotopes of hydrogenas found in nature. Note that the heavier iso-

49

A Little Radiation Physics 45

ISOTOPES

HYDROGEN(STABLE ATOM

DEUTERIUM TRITIUMOTASLE ISOTOPE Of HYDROOENI (RADIOACTIVE ISOTOPE OF INICROSEN)

URANIUM 238(99*% °FORAMINA ASFOUND IN NATURE)

92 PROTONS

146 NEUTRONS

URANIUM 235(0.7% Oft/RAN /,UM AS FOUND IMMATURE)

FIGURE 18

Lopes are a very small fraction of 1. percentof the total amount of hydrogen we find innature. We know that water consists of mole-cules made up of two parts of hydrogen andone part of oxygen. If we make some waterit which the hydrogen is not the normal iso-tope of hydrogen with one proton but thedeuterium isotope with one proton and oneneutron, we will make a water that looks likeWater, tastes like water, and, from the chemicalpoint of view, is water. However, from aneuclear point of view, this is so-called heavywater because it is made with the heavierisotope of hydrogen.

Figure 18 also shows us two different isotopesof uranium. One is called uranium 238; theother uranium 235. Both of these will reactchemically in exactly the same way. There-

LEGEND:= ELECTRON

(-ELECTRICAL CHARGE)

0 = PROTON(+ ELECTRICAL WARM)

= NEUTRON(NO ELECTRICAL cow)

92 PROTONS

143 NEUTRONS

fore, to thr, chemist, a mass of material con-sisting of these two isotopes is uranium.

Atomic Disintegration

Let us consider now What happens when aradioactive isotope gives off radiation, and letus follow one atom of uranium through itssuccessil e disintegrations. We start with anatom of uranium 238, which has 92 protonsand 146 neutrons, as shown in figure 19. Fol-low the process step by step on the chart.

Uranium 238 emits an alpha particle. Analpha particle consists of two protons and twoneutrons, and, therefore, it is obvious that itis an atom. in its own right. It is the nucleusof the helium atom, helium being that atomwhich has two protons and two neutrons. With


DECAY OF A 1/RAN/1/41 ATOMELEMENT AND

ATOMIC WEIGHTTYPE OF

RADIATION EMITTEDNUMBER OF

PROTONS NEUTRONS

URANIUM-236 92 146ALPHA PARTICLE -2 -2

THORIUM-234 90 144BETA PARTICLE +1 -1

PROTACTINIUM-234 91 143BETA PARTICLE +1 -1

URANIUM-234 92 142ALPHA PARTICLE -2 -2

THORIUM-230 90 140ALPHA PARTICLE -2 -2

RADIUM-226 88 138ALPHA PARTICLE -2 -2

RADON-222 86 136ALPHA PARTICLE -2 -2

POLONIUM-218 84 134ALPHA PARTICLE -2 -2

LEAD-214 82 132BETA PARTICLE +1 -1

BISMUTH-214 83 131BETA PARTICLE +1 -1


LEAD-210 82 128BETA PARTICLE +1 -1

BISMUTH-210 83 127BETA PARTICLE +1 -1


LEAD-206 STABLE ATOM 02 124

ELECTRON

BETA PARI7CLE

A NEUTRON CONS /STS CFA PeorDNAND AN ELEMON. Af7FA SIMMSTHE riferRONMETA PAC7e4rNE

NEUTRON NEUTRON SEMMES A Morom.(masa-RimCRUM)

FIGURE 19

the alpha particle thrown out, we now have90 protons and 144 neutrons. Our nucleusnow weighs 234 units, and since the numberof protons has been changed, it is no longerUranium, but is, in fact, Thorium.

Thorium 234 does not emit an alpha particlebut does emit a beta particle. Where does thebeta particle come from ? Remember that wesaid a neutron was electrically neutral. Weknow that an electrically neutral state can bereached when positive and negative chargesbalance one another. Let us consider that a

neutron consists of a proton with an electrontightly tied onto it as shown in figure 19. Thenegative charge of the electron balances thepositive charge of the proton, so we have aneutron. When this negatively charged electronis emitted as a beta particle, the remainder isno longer electrically neutral, but now has apositive charge, so we have changed a neutronto a proton. We have, in effect, added oneproton and subtracted one neutron. We nowhave 91 protons and 143 neutrons. The weightis still 234, but since we have changed thenumber of protons, we have changed the natureof the element, and it is now an atom ofprotactinium.

Protactinium, also emits a beta particle sowe add 1 proton, and subtract 1 neutron, leav-ing 92 protons and 142 neutrons. Its weightis 234, but our element is, of course, againuranium.

Uranium 234 emits an alpha particle, so wesubtract 2 neutrons and 2 protons, and we nowhave 230 particles in the nucleus. Since thenumber of protons is back to 90, we havethorium M.

Thorium 230 emits an alpha particle. Sub-tract 2 protons and 2 neutrons. We now havea weight of 226, and since we have only 88protons in the nucleus, we now have the ele-ment radium.

Radium emits an alpha particle, so we lose2 neutrons and .2 protons, and have 86 protonsand 136 neutrons. Our element is now radon222, which is a gas.

Radon 222 emits an alpha particle, leavingus with 84 protons and 134 neutrons. Again wehaven different elementpolonium 218.

Polonium emits an alpha particle, whichleaves us with 82 protons and 132 neutrons,lead 214.

Lead 214 emits a beta particle which in-creases our number of protons by 1 and de-creases our number of neutrons by 1, leavingus with 83 protons and 131 neutrons. Thisgives us bismuth 214.

Bismuth 214 emits a beta particle which adds1 proton and subtracts 1 neutron. leaving us

51

A Little Radiation Physics 47

84 protons and 130 neutrons. This is polon-ium 214.

Polonium 214 emits an alpha particle whichcosts us 2 neutrons and 2 protons, bringingus down to 82 protons and 128 neutrons fora mass of 210, and the element is lead 210.

Lead R1O emits a beta particle, giving us83 protons and 127 neutrons, whiCh is bi8muth,VO.

Bi8muth, VO emits a beta particle. Add aproton and subtract a neutron, and we have84 protons and 126 neutrons polonium VO.

Polonium VO emits an alpha, which leavesus with 82 protons and 124 neutrons. Thetotal weight is 206; the element is lead 206.

Lead 206 is stable and not radioactive, andwe have reached the end of the line.

Well, that's fine, and all very interesting,and accounts for beta and alpha radiation, butwhat about gamma radiation? Where doesthat come from? Gamma radiation originateswhen the discharge of one of these particlesfrom a nucleus does not take sufficient energywith it to leave the nucleus in quite a con-tented state. If the particle leaving the nu-cleus does not take with it all of the er gythat the atom would like to get rid of in thisparticular disintegration, it throws off someof the energy in the form of gamma radiation.

The foregoing makes it clearer to us whywe can detect gamma radiation from a radiumdial wrist watch. Radium is a pure alphaemitter, but as the decay process goes onthrough the decay chain, the "danghter prod-ucts" of the radium start to build up, and itis from the decay of the vo.rious "daughterproducts" that we receive the gamma radia-tion. Pure elemental radium, freshly prepared,represents only an alpha hazard and couldsafely be handled with the bare hands as faras external hazard is concerned. (Of course,handling it with the bare hands is not a goodidea because of the possibility of introducingsome radium into the body by this means.)After the passage of some time, however, the"daughter products" start to build up, and

alpha, beta, and gamma radiation are all beinggiven off from the radium and its associateddaughters.

It is impossible for us to look at any oneatom and predict exactly when this disintegra-tion process will take place, but if we havea large number of the atoms, we can deter-mine that half of the atoms will disintegratein a given period of time. This is the so-calledhalf-life of a radioactive material and mayrange from fractions of a second up to thou-sands of years. The shorter the half-life, themore highly radioactive the material will be.

Isotopes with very short half-lives are notvery useful because they will decay so rapidlythat they cannot be put to effective use. Iso-topes with half-lives measured in hours ordays, can be put to practical use, but thisrequires close scheduling of the use of theisotopes with its manufacture, air express ship-ment, immediate pickup, etc.

Radiation Energy

From the natural decay of radioactive ma-terials, therefore, we get energy which can beused in a number of ways. The energy emitssignals which can be detected, and thus we cantrace processes in man, plants, and animals.It will make the air electrically conductive,and we can use it to bleed off static electricity.It has the power to destroy living tissue, and,therefore, we can use it to kill off bacteria ormalignant growths in man. It has the powerto bring about changes at certain stages inchemical processes just as other applications ofenergy, such as heat and light can do, and,therefore, we find it useful in the manufactureof certain products. In small amounts it canbe converted into electrical energy.

However, as important as this source ofradiant energy is, we cannot use it for anenergy source such as we need for the gen-eration of substantial quantities of electricalpower to replace or to supplement our rapidlyexhausting stock of fossil fuels, such as oil,


coal, and natural gas, or our limited suppliesof water power. In order to do this we haveto look to another physical property of a veryfew of the radioisotopes. This is not radiationat all, but atomic fission.

Fission Energy

Einstein demonstrated mathematically thatmass could be converted to enerv. If we wereto take a large heavy atom like uranium andbreak it up into two smaller atoms, we wouldfind that the neutrons and protons in the twosmaller atoms do not weigh quite as much asthe neutrons and protons in the uranium atomdid. Some of the mass of the nucleus of theatom has been converted to energy.

A neutron makes a good atomic bullet be-.cause it is electrically neutral, and, therefore,is not repelled by the positive charge of the

53

nucleus. So, if we fire a neutron at a uraniumnucleus at the proper speed, the neutron willenter the nucleus, break it up into two smalleratoms, and a certain amount of energy willbe released. The problem, of course, is thatit takes quite a bit of effort to fire the neutronin the first place, and this process, by itself,would not be productive of any useful energy.

The uranium 235 isotope is unique in thefact that when it is hit by a neutron and theatom is broken up into smaller particles, someof the neutrons in the uranium nucleus in turnbecome nuclear bullets and fission other atomsof the same material. This chain reaction,by which one neutron can be used to release theenergy from an atom, and, in turn, createmore than one additional bullet which willcarry on the process, is the secret of releasingmassive quantities of energy from the atom..

Chapter XI

ATOMIC FISSION

We now sea that there is nothing equivalentbetween the terms "radioactive" and "fission-able." Just because a material is radioactive,it is not necessarily fissionable, and most ofthe radioisotopes which are handled in com-merce and industry are not fissionable. Manypeople are convinced, for instance, that if aperson had a sufficient quantity of cobalt 60on hand, a nuclear chain 'reaction could bebrought about. This, of course, is not thecase. We must have a material capable ofkeeping up and multiplying the chain reactionprocess so that a large number of fissions can

be made to take place in a relatively shortspace of time.

There are only two materials readily avail-able to us which have this property. One isuranium 235, which is an isotope of uranium,about 1 /440th of uranium as it is found in na-ture, the balance being mostly U238. The otherfissionable material is plutonium. Plutoniumis not a natural element, but a man-madeelement created from uranium in nuclear re-actors.

If we take some uranium as we find it innature, and, by a complicated physical process,

FIGURE 20

49

54


CRITICAL MASS CONCEPT

NUCLEI OP ME1/135 ATOMS

SKETCH A

wefle.::.11' %t .

SUB. CRITICAL MASS OFFISSIONABLE MATER /AL

SKETCH C

O .

.11:-- :a-ADDI770NAL

SUBCRI77CAL MASSADDED

ESCAPINGNEUTRONS

1161' to& to

OR

SU8CRI77CAL MASS

saw/ E_ goad,.I. no o ::

it

f000

e MASSES--NEFO NOT

TOUCH

SKETCH BSPONTANEOUS

FISSION/N6

MORE NEUTRONS ESCAPETHAN ARE BEING PRODUCED

SKETCH I)

1 ,,,,(b.°. ...- w -411.

'9.0e

ADDITION AI SUB. CR/7701 AMSS ADDEO (WITHEACH ADDITION ME MASS HAS BEEN /N-CREASED /N RELATION ry THESURFACE AREA)

NEUTRONS

1 .-,..1

.. .. ......:.. ....,,,%-,,. ."*2 'ill - 0- C.: ai I, 0e -...---Agti

FIGURE 21

SKETCHPISS/ONPRODUCTS

MORE NEUTRONS ARE 57111 ESCAPINGTHAN ARE BEING PRODUCED.

SKETCH F

MA.5 /SNOW CRITICAL (AfORE NEO7RONSAdt BEING PRODUCED THAN ARE ESCAPING

fr'ROM THE ENTIRE SURFACE AREA)

HEAT

CRINAL MASSMELTS DOWN770/3CHANGING 77IE SHAPE (SURFACE

AREA /S INCREASED CAUSINGMORE IIEUTRONS TO rsCARETHAN ARE BENG PRODUCED)

/.1 MASS 77/EN BECOMES SUB-CRITICAL

Atomic Fission 51

take out many of the atoms of uranium 238,we will, thereby, increase the proportion ofuranium 235. This is so-called enri, led uran-ium. This is to say, it has been enriched inthe proportion of the fissionable uranium 235isotope. The degree of enrichment is expressedin percent. Normal uranium is 0.7 percentenriched. This is uranium as we find it innature. If we 'take out enuugh of the U288isotope in the gaseous diffusion plant at OakRidge, we increase the percentage of 13285 inthe resultant product. If we increase the per-centage to 2 percent, we have 2 percent en-riched material. If we increase the percentageof U235 to 10 percent, we have 10 percent en-riched uranium, which is still uranium. Chem-ically, it reacts like uranium; it looks likeuranium; it is uranium. The idea is quitesimilar to picking slate out of low-grade coalto increase the BTU content, per ton, of theresultant product.

Figure 20 shows us what happens when aneutron strikes an atom of fissionable material,whether it is enriched uranium or plutonium.The atom splits, some energy is released,smaller atoms (fission products) aro left fromthe pieces of the uranium atom, and 1 to 3more neutrons are freed to continue the fissionprocess.

Since some of the atoms of uranium arespontaneously fissioning all of the time, it isquite possible for a spontaneous chain reactionto take place if a sufficient quantity of thematerial is assembled in the proper shape.

,e quantity of a fissionable material whichwill provide a self-sustaining chain reactionis known as the critical mass of the material.

Let us see what happens as we assemble acritical mass piece by piece. Figure 21 showsus what happens step by step.

In "sketch A" we see a piece of fissionablematerial. We are no longer concerned with theelectrons. Each one of the dots represents anucleus of a uranium 235 atom. In "sketchB" we see what happens when one of the atomsspontaneously fissions and throws out neutronswhich start the chain reaction. Even though

uranium is a heavy, dense material, it is stillmostly space. Because we have a relativelysmall amount of the material in proportionto the surface area, neutrons can readily escapefrom the mass. The result is, that while littlefirecrackers of chain reaction are starting fromtime to time, so many neutrons get lost throughthe surface that the process does not multiplyitself.

In "sketch C" we add to the first subcriticalmass of fissionable material an additional sub-critical mass of fissionable material. Some ofthe neutrons which were escaping freely fromthe first piece of fissionable material now findtargets in the second piece of fissionable ma-terial, and additional fissions take place asshown in "sketch D." However, we still havesuch a large surface to mass ratio that theneutrons readily escape out of the mass, andwe still cannot get a self-sustaining chainreaction because more neutrons are being lostthan are being created.

"Sketch E" shows us what happens in thisparticular instance wh mi we add a third pieceof fissionable material. We notice that we havegreatly increased the mass of the material with-out greatly increasing the surface area. Asthe chain reaction starts and the neutrons startto multiply as shown in "sketch F," there isinsufficient surface area for the neutrons toescape. As soon as we make one more neutronthan we have lost, the mass is critical, and themultiplication of the chain reaction starts toincrease at a fantastic rate. The fact thatthree pieces are used here is only for exampleand is not related to any specific situation.

Because of the energy being released, themass starts to heat up. As the fissionable ma-terial heats, it eventually reaches the meltingpoint. When a mass melts down, the surfacearea is increased, the neutrons can again freelyescape in a greater number than they are beinggenerated, and the result is that the chainreaction comes to a halt as shown in "sketchG." This will all take place in an instant.

At the time the process was going on, therewas a burst of gamma radiation, which is


extremely hazardous to people in the area.There was a burst of neutron radiation, whichis also hazardous to those immediately present,and a certain amount of heat was given off.In addition, fission products, giving off a va-riety of radiation, and with a variety of half-lives, were created from the fissioned atomsof the fissionable material. Because of the heatgenerated, the .fission products may be spreadaround the area by convention currents of hotair, so that the area may be highly con-taminated with radioactive material.

If any person was present close by whenthis took place, he could be seriously injuredand in danger of death. A person enteringthis area afterwards would necessarily have tobe protected against the gamma radiation fromthe fission products by restricting his time inthe area to the minimum, and against the betaradiation from the fission products by suitableclothing.

There would not be an atomic bomb typeexplosion in this accident, however, because wedid not have the hardware that goes to makean atomic bomb. The situation is similar tothat of a firecracker. When we light a fire-cracker in the normal manner, we have anexplosion. When we take the firecracker, breakit open, and spread the powder out on theground, and then ignite the powder, we get themine energy release, but we do not have anexplosion because we do not have the physicalform necessary to make a firecracker.

So far, we have not seen anything reallyuseful. We know that if we take a fissionablematerial and assemble a critical mass of it inour laboratory that we can have a serious ac-cident; the person performing the experimentmay be killed (though persons as close cs12 feet have s irvived such an accident) ; anthe laboratory may be heavily contaminated.

Let us see how we might control this opera-tion to our benefit. Figure 22 shows us thesame array of pieces of fissionable material,but, in this case, we hrse placed between ourtwo subcritical masses a rod made of an ele-ment called boron. Boron has a characteristic

5"

that it soaks up neutrons as a sponge soaksup water. It is called a neutron absorber.Because of this, we would not get any appre-ciable interaction between any neutrons beingtlnown off by ec,ch of the pieces of fissionablematerial as the boron would have absorbed thegreatest percentage of the neutrons reachingit. If we slowly pulled out our boron roduntil we reached the point where we were justmaking enough neutrons to keep our chainreaction going, our uranium would heat up.

If we removed the heat from the uraniumwith a heat exchange medium, such as water,an organic solvent, a gas, or a liquid metal, wewould keep the uranium from getting too hot,and we could exchange the heat from the cool-ing medium to water to make steam. When wehave done this, we have built an atomic powerreactor.

This is the ba3ic principle of the control ofatomic energy for the generation of power.Some reactors use natural uranium, rather thanenriched uranium. Some work is being doneon plutonium fuel reactors. Reactors vary inthe arrangement of the material. In some re-actors, the fuel is placed in the form of solidrods; in other types the fuel is slurried in aliquid. Reactors vary also in the nature ofthe material used to cool the reactors.

If something starts to go wrong with our"reactor," we would simply shove the boronrod in all the way, absorb neutrons, and ourreactor would stop instantly. This emergencyshutdown of a reactor is what is known as the((scram." Boron and similar materials whichstop the chain reaction are called reactorct ffp040113.

Figure 23 shows us how we use a reactorto create radioactive isotopes and to changeelements from one species to another. Into ahole in our reactor, we insert some cobalt metal.Cobalt, as we find it in nature, has 27 protonsand 32 neutrons. There is no other naturalisotope of cobalt. When we shove a rod ofcobalt into the reactor, the millions and billionsof atoms of .cobalt are subjected to an intensebombardment of neutrons, the so-called "neu-

Atomic Fission 53

ATOMIC REACTOR CONCEPTSKETCH A

-muniummituniontn MASSES OF FISSIOIMBLE

MATER/AL BUILT OP 777 PRODUCEA CRITICAL MASS WITH AN UN-CONTROLLED CHAIN REACT /ON

SKETCH B

BORON ROD USED TOABSORB NEUTRONS

t t f t ill %III SISS I SISO

BORON RODADJUSTABLETO CONTROL THECHAIN REACT/ON

V NI.

/(1115111111( (ki"t "EVEN IN A CONTROLLED CHAIN REACTIONTHE HEAT PROOCE0 WOULD CAUSE AMELTDOWN Of nie MASS, IF NOTREMOVED.

SKETCH C

BIOLOGICAL SHIELD //EAT EXCHANGERYM1

1.041,1LE41 1.1LIZEM i IJcrckwei J

16r. 01117

"Il;l

AW.1I

.TZiff " v

c

INLr'lm.. INC7=a1.7..ca.131r1L.T-1P_,.1

STWI 77/R0/NE

ELECTRICGENERATOR

CONDENSER71/801 WWII CONTAIN A LI (11//0 7VTRANSFER NEAT PROM VIE REACTORTO THE NEAT EXCHANell? WNERO'=Am /5 611114A7W0 7V RUN NE ?wow

FIGURE 22

56

PUMPS


NEUTRON CAPTURE( HOW TIONGS BECOME RADIOAC771/E)

co8ALT,59127PROToNS1.32*M/774'0MS

31.-COSAL7:53 BF /NO /M.,SERreo

IN THE REACTOR

REACTOR

imminniumidis71 If:#

NEUTRON FLUX

FIGURE 23

tron flux." A few of the atoms of cobalt,possibly one in a billion, capture neutrons andnow have 33 neutrons instead of 32. Theseatoms are no longer cobalt 59, as we find it innature, but cobalt 60. Cobalt 60 is radioactive,gives off gamma radiation, some beta radiation,and has a half-life of about 5.4 years.

When we take our sample of cobalt out ofthe reactor, it is still cobalt chemically; pos-sibly one-billionth of it is radioactive cobalt.It would be extremely difficult to separate theradioactive cobalt from the nonradioactive co-balt, so we don't even try. The cobalt 60, asit is now called, is widely used for sources ofpenetrating external rail' ation, such as theradiography of casting, for deep therapy ofcancer patients, etc. The cobalt was maderadioactive by neutron capture.

Instead of cobalt, let us insert into our re-actor some mercury 200. Mercury 200 has 80protons and 120 neutrons. In the reactor, atiny fraction of the atoms of mercury capturea neutron. They now have 80 protons and121 neutrons.

59

1121WS UP I AVIT/TON = 13=10)C08A0:6.01

COO4LT-59 AFTER OF/NO / N 71/EREACTOR BECOMES COBALT -60

WHICH IS RAO/OACTWE

NOTE: ONLY A SMALL NUMBER OF COB4LS3 AMOSBECOME RA 'oAcrive COFI1L7:60 BY NEUTRONCAPME.7,..SOEPENDMIG ON NO* LONG 77/EC08.4715-9 /3 LOFT /N THE REACTOR ANDTHE STRENGTH OF THE NEUTRON FLUX.

It so happens that this mercury 201, whenexcited, throws out a proton, leaving us with79 protons and 121 neutrons. Since we havechanged the number of protons, we havechanged the nature of the substance. Theseare no longer atoms of mercury, but atoms ofthe substance with 79 protons in the nucleusgold. We have made gold 200, a radioactiveisotope of gold. Since it is a different elementfrom mercury, we can separate it by chemicalmeans. This is shown in figure 24.

We haVe seen, therefore, that to make sub-stances radioactive, we must subject them to atremendous bombardment of atomic particles,such as neutrons in a nuclear reactor. Thereis another very precise way in which smallquantities of radioisotopes can be created. In-stead of the shotgun technique of the nuclearreactor, we can set up a target material andbombard it with nuclear particles at highspeed. We get the particles up to high speedby whirling them around and around, as wewould do with a slingshot. Machines whichdo this are called particle accelerators. Some

Atomic Fission 55

TRANS/WI/TAT/ON(HOW AN ELEMENT IS CHANGED WV A DIFFERENT ONE)

80 PROTONSMERCURY.200 {120 NEUTRONS*

MERCURY-200 BEING INSERTE0/N THE REACTOR

REACTOR

NEUTRON FLUX

pic EJECTS -731011)200a UP = 80 R. mER01.2 pRonw121Ninveav 12IN.

"'MERCURY 200 AFTER BEING IN 771EREACTOR BECOMES GOLD 200 BYNEUTRON CAPTURE AND THEN BYEJECTING ONE PROTON.

NOTE: ONLY A SMALL NUMBER OF MERCURY200 ATOMSBMW RADIOACTIVE 00L0-200 TINS DEPEND-/NS ONHOW LONG THE MERCURY-200 AS LEFTMe THE REACTOR AND THE STRENGTH OfTHE NEUTRON FLUX.

FIGURE 24

types of particle accelerators, such as the linearaccelerator, get the particle going at highspeed, but in a straight line rather than aroundand around in a circle.

We can get radioactive isotopes, therefore,as fission products by gathering up and sep-arating out the fission products from the wastematerial of an atomic reactor; by neutron cap-ture in which the target material captures aneutron but is not changed to another sub-stance; and by transmutation, that is, by thechanging of one element to another, as wehave seen in the case of the mercury.

Things cannot be made radioactive by beingsubject to gamma radiation. Radioactivity isnot induced in materials contaminated withradioactive substances. They are made radio-active by being subject to an intense 'neutronflux.

Return to "sketch D" of figure 21, a so-called subcritical mass; that is, an insufficientamount of material to sustain chain reaction.

Suppose we surround this material with asubstance which causes neutrons to bounce

back into the fissionable material. So to speak,we put the cushion upon the billiard table.We see that very few neutrons would thenescape, and, in effect, the neutrons would havemore than one chance to effect a collision witha target. Such a material is called a reflector,and, of course, it is designed into the construc-tion of an atomic reactor in order to conservethe neutrons.

Our interest in reflection is the fact thatmany common substances, such as those richin hydrogen, or other light elements, are goodneutron reflectors, and, therefore, accidentallyplacing a material which can cause neutronreflection close to a subcritical mass of materialmight conceivably bring about a nuclear chainreaction.

For neutrons to be able to enter an atom andbring about fission, it is necessary that theybe traveling at just the proper speed. Mate-rials which are used to slow down the neutronsto the proper speed are called moderators. Theaccidental mixing of a moderator with a fis-sionable material might bring about such a

60


condition. For instance, water is both a re-flector and a moderator of neutrons. A bucketof chips of fissionable material might be asuberiticsi mass. Filling the bucket with water,however, might bring about enough moderationand reflection of neutrons to change the situa-tion to a critical mass condition.

What does all of this mean to us from thepractical safety point of view? All threefatal accidents due to radiation in the atomicenergy program took place in connection withthe handling of fissionable materials. Figure25 shows what happened when sufficient reflec-tion to bring about criticality, was providedaccidentally.

When fissionable materials are handled inour plants, it is necessary that we strictly com-ply with all regulations which are laid down.Naturally, the regulations take advantage ofthe various factors of spacing, shape, modera-

tion, reflection, etc., which we have discussed.For instance, fissionable materials in storageare spaced certain distances apart. Whereseveral projects are going on in a plant, theremust be control of the movement of the ma-terials within the plant; otherwise, a man fromproject A returning some material to the vaultcould conceivably pass a man from project Bremoving some material from the vault in acorridor and the exact situation be set up fora spontaneous chain reaction. The situationneed exist only for a fraction of a second foran accident to happen.

Each individual operation must be carefullystudied by personnel trained in the field ofcriticality. When they have completed theirstudy, they lay down regulations for the safeconduct of the operation. Very many safetyfactors are built in, and basic to their safetyconsideration is that at least two entirely un-

FIGURE 25.M a y 1946; one man was killed in this criticality accident. The others were injured in varyingdegrees, but survived.

61

Atomic ,Fission 57

related precautions must be violated to set thestage for an accident.

In many other fields of safety, we are con-stantly bombarded with the philosophy thatthe man on the job is his own best safety en-gineer, since lie best knows the hazards of thejob. This is not true of criticality safety. Inthis area, we must get "the word" from theman qualified to give it, and then follow itout to the letter. If some circumstance ariseswhich makes it impossible for us to carry outthe precautions as previously laid down, wecannot use our own judgment and modify thesituation. We must return to the man whomade the rule, explain out circumstances, andask him for a new set of rules.

Materials may look the same and may evenbe called by the same name, but may varygreatly in their criticality characteristics dueto the assay of the material, the presence orabsence of poison, the density of the material,the shape of the material, etc. So, we cannotdraw the conclusion that the job we are work-ing on this week is the same as the one we didlast week. We cannot assume that it is per-missible to transfer a job from lathe No. 1 tolathe No. 2 because lathe No. 1 has brokendown, even though we were allowed to do solast week when lathe No. 1 broke down.

In the transportation of fissionable material,it is obvious that precautions must be takento prevent two or more subcritical masses fromcoming together as a result of an accident andcreating a critical mass situation. Since wateris a moderator and a reflector, there is hazardin the fact that the vehicle may be submergedentirely in water.

Accidents are guarded against by a numberof precautions taken in transportation, amongthem the construction of containers called bird-cages. Figure 26 shows a typical birdcage.The purpose of the birdcage, which is veryheavily built, is to keep subcritical masses offissionable material from approaching eachother any closer than the outer limits of thebirdcage.

For experimental work in atomic energy, itis often necessary that a source of neutronsbe provided. Such sources are made up fromalpha emitters, such as radium or polonium,mixed with beryllium. When an energeticparticle from the polonium strikes the beryl-lium, a neutron is knocked out. Such sources

TYPICALHB/RDCAGE"1/SED FOR SHIPPINGFISSIONABLE MATERIALS

FIGURE 26

present a neutron radiation hazard in the bodywhich they might strike, though the principalproblem has been the formation of cataractsin the eyes of scientists who looked direztlyinto neutron beams.

We saw that lead and other such materialsare used for gamma radiation shielding be-cause of the large number of electrons. Anelectron, of course, is not much help in stop-ping a neutron. To stop a neutron, we needan element which looks as much like a neutronas possible, so we will get a so-called billiardball collisionthat is, there will be an almostcomplete transfer of energy from the flyingneutron to the particle trying to stop it.


The element which looks most like a neu-tron is hydrogen, which consists of one proton.Therefore, hydrogenous materials are used forneutron shielding. The cheapest, commonlyavailable such material is paraffin, which has ahigh hydrogen content. Paraffin-filled con-tainers are used for the shipment of neutronsources. Paraffin and water, which also con-tains large amounts of hydrogen, are used forshielding around devices, such as cyclotrons.

Special instruments and film badges, sensi-

6 a

tive to neutrons, are used where there areneutron hazards.

The Safety and Fire Protection Branch,USAEC, plans to prepare a series of Parts IIto this publication relating the material con-tained herein to the specific problem of vari-ous fields of endeavor such as fire departments,police departments, transportation, etc. Ad-dress inquiries to: Chief, Safety and Fire Pro-tection Branch, USAEC, Washington 25, D.C.

Appendix A

101 ATOMIC TERMS AND WHAT THEY MEAN

IWe are grateful to the Esso Research and Engineering Company for permission to reprint "101 Atomic Terms and What They Mean")

accelerator A device for imparting very high velocityto charged particles ;such as electrons* or protons.These fast particles can penetrate matter and areknown as radiation. Fast pa., :eta of this type areused in research or to study the structure of theatom itself.

activation Making a substance artificially radioactivein an accelerator such at a cyclotron or by bombard-ing it with neutrons.

alpha particle (alpha ray, alpha radiation) A smallelectrically charged particle of very high velocitythrown off by many radioactive materials, includinguranium and radium. It is identical with the nu-cleus of a helium atom and is made up of two neu-trons and two protons. Its electric charge is posi-tive and twice as great as that of an electron.

atom The tiny "building block" of nature. All ma-terials are made of atoms. The elements, such asiron, lead and sulfur, differ from each other becausethey contain different atoms. Atoms are unbeliev-ably small. No one has ever seen one. There aresix sextillion (6 followed by 21 zeros) atoms in anordinary drop of water. The word "atom" comesfrom the Greek word meaning indivisible. Nowwe know it can be split and consists of an inner core(nucleus) surrounded by electrons which rotatearound the nucleus like the planets around the sun.

atomic energy Energy released in nuclear reactions.Of particular interest is the energy released when aneutron splits an atom's nucleus into smaller pieces( fission) or when two nuclei are joined togetherunder millions of degrees of heat (fusion). "Atomicenergy" is really a popular misnomer. It is morecorrectly called "nuclear energy."

atomic number The number of protons (positivelycharged particles) found in the nucleus of an atom.All elements have different atomic numbers. Theatomic number of hydrogen is 1, that of oxygen 8,iron 26, lead 82, uranium 92.

atomic theory Since the time of the ancient Greeksman has held the theory that ell matter is composedof tiny, invisible particles called atoms. It remainedfor the chemists and physicists of the 19th and 20th

*Italics indicate key word* defined in this pleasant.

centuries to verify the existence of the atom andthe validity of the atomic theory.

atomic weight The atomic weight is approximatelythe sum of the number of protons and neutronsfound in the nucleus of an atom. The atomic weightof oxygen, for example is approximately 16 (actuallyit is 16.0044)it contains 8 neutrons plus 8 protons.Aluminum is 27it contains 14 neutrons and 13protons.

atom smasher A machine (an accelerator) thatspeeds up atomic and sub - atomic particles so thatthey can be used as projectiles to literally blastapart the nuclei of other atoms.

autoradiography Self-portraits of radioactive sourcesmade by placing the radioactive material next tophotographic film. The radiations fog the film leav-ing an image of the source. It was such self-por-traits that led to the discovery of radioactivity.

background Background radiation is always detectedby a counter. It is caused by radiation coming fromsources other than the radioactive material to bemeasured. This "background" is primarily due tocosmic rays which constantly bombard the earthfrom outer space.

beta particle (beta radiation) A small electricallycharged particle thrown off by many radioactive ma-terials. It is identical with the electron and possessesthe smallest negative electric charge found in nature.Beta particles emerge from radioactive material athigh speeds, sometimes close to the speed of light.

betatron A large doughnut-shaped accelerator inwhich electrons (beta particles) are whirled througha changing magnetic field gaining speed with eachtrip and emerging with high energies. Energies ofthe order of 100 million electron volts have beenachieved. The betatron produces artificial betaradiation.

her A billion electron volts. An electron possessingthis much energy travels with a speed close to that oflight-186,000 miles a second.

betatron A huge circular accelerator such as the onelocated at the University of California. Protons arewhirled through the 160-foot "doughnut" betweenthe poles of a magnet weighing 13,000 tons. It is de-signed to produce energies of 10 billion electronvolts.

"64

59


binding energy The energy which holds the neutronsand protons of an atomic nucleus together.

bombardment Shooting neutrons, alpha particles andother high energy particles at atomic nuclei usuallyin an attempt to split the nucleus or to fortr. a newelement.

breeder A reactor which is producing more atomicfuel than it is consuming, A nonfissionable isotope,bombarded by neutrons, is transformed into a fission-able material, such as plutonium, which can be usedas fuel. Scientists are working toward the day whenall the material burned in reactors will be replacedthrough this process.

Cerenkov radiation An eerie blue glow given off byelectrons traveling in a transparent material such aswater. It is this radiation which. is visible duringthe operation of some nuclear reactors.

chain reaction When a fissionable nucleus is split bya neutron it releases energy and one or more neu-trons. These neutrons split other fissionable nucleireleasing more energy and wore neutrons making thereaction self-sustaining.

charge The fuel (fissionable material) placed in areactor to produce a chain reaction.

cloud chamber A glass-domed chamber filled withmoist vapor. When certain types of atomic particlespass through the chamber they leave a cloud-liketrack much like the vapor trail of a jet plane. Thispermits scientists to "see" these particles and studytheir motion.

cobalt 60 A radioactive isotope of the element cobalt.Cobalt 60 is an important source of gamma radiationand is used widely in research.

coffin A thick-walled container (usually lead) usedfor transporting radioactive materials.

compton effect The glancing collision' of a gamma raywith an electron. The gamma ray gives up part ofits energy to the electron.

control rod A rod used to control the power of anuclear reactor. The reactor functions through thesplitting of nuclear fuel by neutrons. The controlrod absorbs neutrons which would normally splitatoms of the fuel. Pushing the rod in reduces therelease of atomic power. Pulling out the rod in-creases it.

converter A reactor which uses one kind of fuel andproduces another. For example a converter chargedwith uranium isotopes might consume Uranium 235and produce plutonium from Uranium 238.

core The heart of a nuclear reactor where the nucleiof the fuel fission (split) and release energy. Thecore is usually surrounded by a reflecting materialwhich bounces stray neutrons back to the fuel.

cosmotron A huge accelerator, one of the atomic'tuns," located at Brookhaven National Laboratory.It speeds up particles to the billion electron volt

range. The Brookhaven machine has a magnetweighing 2,200 tons.

counter A device for counting nuclear disintegrationsto measure radioactivity. The signal which an-nounces a disintegration is called a count.

critical mass The amount of nuclear fuel necessaryto sustain a chain reaction. If too little fuel ispresent too many neutrons will stray and the re-action will die out.

curie A measure of the rate at which a radioactivematerial throws off particles. The radioactivity ofone gram of radium is a curie. It is named forPierre and Marie Curie, pioneers in radioactivityand discoverers of the elements radium, radon, andpolonium.

cutie-pie A portable instrument equipped with a di-rect reading meter used to determine the level ofradiation in an area.

cyclotron A particle accelerator. In this atomic"merry-go-round" atomic particles are whirledaround in a spiral between the ends of a huge magnetgaining speed with each rotation in preparation fortheir assault on the target material.

decay When a radioactive atom disintegrates it is saidto decay. What remains is a different element. Anatom of polonium decays to form lead, ejecting analpha particle in the process.

deuterium Heavy hydrogen. The nucleus of heavyhydrogen is a deuteron. It is called heavy hydro-gen because it weighs twice as much as ordinaryhydrogen.

deuteron The nucleus of an atom of heavy hydrogencontaining one proton and one neutron. Deuteronsare ofter used as atomic projectiles.

dosimeter (dose meter) An instrument used to deter-mine the radiation dose a person has received.

electron A minute atomic particle possessing thesmallest amount of negative electric charge foundin nature. In an atom the electrons rotate around asmall nucleus. The weight of an electron is so in-finitesimal that it would take 500 octillions (500followed by 27 zeros) of them to make a pound. Itis only about a two-thousandth of the mass of aproton. or neutron.

electron volt (ev) A small unit of energy. An elec-tron gains this much energy when it is acted uponby one volt.

element A basic substance consisting of a "family"of naturally occurring isotopes. For example, hy-drogen, lead and oxygen are elements. All atomsof an element contain a definite number of protonsand thus have the same atomic number.

film badge A piece of masked photographic film wornlike a badge by nuclear workers. It is darkened bynuclear radiation, and radiation exposure can bechecked by inspecting the film.

101 Atomic Terms and What They Mean 61

fission Tie splitting of an atomic nucleus into twoparts accompanied by the release of a large amountof radioactivity and heat. Fission reactions occuronly with heavy elements such as uranium and plu-tonium.

fissionable A nucleus which undergoes fission underthe influence of neutrons, even of very slow neutrons.Uranium 235, an isotope of uranium with mass num-ber 235, is fissionable. Plutonium is also fissionable.

fusion The joining of atomic nuclei to form a heaviernucleus, accomplished under conditions of extremeheat (millions of degrees). If two nuclei of lightatoms fuse, the fusion is accompanied by the releaseof a great deal of energy. The energy of the sunis believed to be derived from the fusion of hydrogenatoms to form helium.

gamma rays (gamma radiation) The most penetrat-ing of all radiations. Gamma rays are very highenergy X-rays.

geiger counter A gas-filled electrical device whichdetects the presence of radioactivity by counting theformation of ions.

half-life A means of classifying the rate of decay ofradioisotopes according to the time it takes themto lose half their strength (intensity). Half livesrange from fractions of seconds to billions of years.Cobalt 60, for example, has a half-life of 5.3 years.A radioactive material loses half its strength whenits age is equal to its half-life.

heavy hydrogen Same as deuterium.heavy water Water which contains heavy hydrogen

(deuterium) instead of ordinary hydrogen. It iswidely used in reactors to slow down neutrons.

hot A colloquial term meaning highly radioactive.ion Usually an atom which has lost one or more of

its electrons and is left with a positive electricalcharge. There are also negative ions, which havegained an extra electron.

ionization chamber A device roughly similar to ageiger counter and used to measure radioactivity.

isotope Two nuclei of the same element which havethe same charge but different: masses are calledisotopes. They contain the same number of pro-tons but a different number of neutrons. Uranium238 contains 92 protons and 146 neutrons while theisotope U235 contains 92 protons and 143 neutrons.Thus the atomic weight (atomic mass) of U222 isthree higher than that of U222.

key Kilo electron volts or 1,000 electron volts. A unitof energy.

kilocurie 1,000 curies. A unit of radioactivity.linear accelerator A machine for speeding :iii charged

particles such as protons. It differs from other ac-celerators in that the particles move in a straightline at all times instead of in circles or spirals.

master slave manipulators Mechanical hands use4 tohandle hot materials. They are remotely controlledfrom behind a protective shield.

meson A particle which weighs more than the electronbut generally less than the proton. Mesons can beproduced artificially. They are also produced bycosmic radiation (natural radiation coming fromouter space). Mesons are not stablethey disinte-grate in a fraction of a second.

mev Million electron volts.millirofmtgen One one-thousandth of a roentgen. A

roentgen. A unit of radioactive dose.moderator A material used to slow neutrons in a

reaotor. These slow neutrons are particularly effec-tive in causing fission. Neutrons are slowed downwhen they collide with atoms of light elements suchas hydrogen and carbon, two common moderators.

molecule The smallest unit of a compound. A watermolecule consists of two hydrogen atoms combinedwith one oxygen atom. Hence the well-known for-mula, H2O.

monitor A radiation detector used to determinewhether an area is safe for workers. A cutie-pieis a portable monitor.

neutron One of the three basic atomic particles.The neutron weighs about the same as the proton,and, as its name implies, has no electric charge.Neutrons make effective atomic projectiles.

nuclear bombardment The shooth2g of atomic pro-jectiles at nuclei usually in an attempt to split theatom or to form a new element.

nuclear energy The energy released in a nuclear re-action, such as fission or fusion. Nuclear energy ispopularly, though mistakenly, called atomic energy.

nuclear reaction Result of the bombardment of a nu-cleus with atomic or sub-atomic particles or veryhigh energy radiation. Possible reactions are emis-sion of other particles or the splitting of the nucleus(fission). The decay of a radioactive material isalso a nuclear reaction.

nucleonics The application of nuclear science andtechniques in physics, chemistry, astronomy, bio-logy, industry and other fields.

nucleus The inner core of the atom. It consists ofneutrons and protons tightly locked together.

pair production The conversion of a gamma ray intoa pair of particlesan electron and a positron. Thisis an example of direct conversion of energy intomatter according to Einstein's famous formula :

--nic2; (energy) = (mass) x (velocity of light)2.photoelectric effect Occurs when an electron is

knocked out of an atom by a light ray or gamma ray.This effect is used in an "electric eye". Light fallson a sensitive surface knocking out electrons whichcan then be detected.

66


photon A bundle (quantim) of radiation. Consti-tutes, for example, X-rays and light. In certainprocesses gamma rays behave as photons.

pig A container (usually lead) used to ship or storeradioactive materials. The thick walls protect theperson handling the container from radiation.

pile A nuclear reactor. Called a pile because theearliest reactors were "piles" of graphite blocks anduranium Cups.

pitchblende An ore containing both uranium andradium. The Curies had to purify tons of pitch-blende to obtain a barely visible speck of radium.

plutonium A heavy element which undergoes fissionunder the impact of neutrons. It is a useful fuel innuclear reactors. Plutonium does not occur in na-ture but can be produced and "burned" in reactors.

positron A particle which has the same weight andcharge as an electron but is electrically positiverather than negative. The positron's existence waspredicted in theory years before it was actually de-tected. It is not stable in matter.

proton One of the basic particles of the atomic nucleu8(the other is the neutron). Its charge is as largeas that of the electron, but positive.

Q-value The energy liberated or absorbed in a nuclearreacton.

rabbit A capsule which carries samples in and out ofan atomic reactor through a pneumatic tube. Pur-pose is to permit study of the effect of intense radia-tion upon various materials.

radiation (radioactivity) The emission of very fastatomic particles or rays by nuclei. Some elementsare naturally radioactive while others become radio-active after bombardment with neutrons or otherparticles. The three major forms of radiation arealpha, beta and gamma, named for the first threeletters of the Greek. alphabet.

radiochemistry That phase of chemistry concernedwith the properties and behavior of radioactive ma-terials.

radioisotope A radioactive isotope of an element. Aradioisotope can be produced by placing material ina nuclear reactor and bombarding it with neutrons.Radioisotopes are being used today as tracers inmany areas of science and industry and are at pres-ent the most important peacetime contribution ofatomic energy.

radium One of the earliest known naturally radio-active elements. It is far more radioactive thanuranium and is found in the same ores.

reactor An atomic "furnace". In a reactor, nucleiof the fuel undergo fission under the influence ofneutrons. The fission produces new neutrons, andhence a chain reaction. This release large amountsof energy. This energy is removed as heat which

6"

may be used to make steam for use in generationof electricity.

roentgen A unit of radioactive .dose, or expmre.The Atomic Energy Commission has established aconservative limit of exposure for the protection ofatomic workers.

scintillation counter A device for counting atomicparticles by means of tiny flashes of light (scintilla-tions) which the particles produce when they strikecertain crystals.

shield A wall which protects workers from harmfulradiations released by radioactive materials.

slug A "fuel element" for a nuclear reactor, a pieceof fissionable material. The slugs in large reactorsconsist of uranium metal coated with aluminum toprevent corrosion.

source Any substance which emits radiation. Usuallyrefers to a piece of radioactive material convenientlypackaged for scientific or industrial use.

synchrotron An accelerator used to achieve highervelocities for atomic particles than is possible in aconventional cyclotron.

thermonuclear reaction a fusion reaction. that is, areaction in which two light nuclei combine to forma heavier atom, releasing a large amount of energy.TU3 is believed to be the sun's source of energy. Itis called thermonuclear because it occurs only at avery high temperature.

thorium A heavy elencent. When bombarded withneutrons thorium changes into uranium becomingfissionable and thus a source of atomic energy.

tracer A radioisotope which is mixed with a stablematerial. The radioisotope enables scientists totrace the material as it undergoes chemical andphysical changes. Tracers are being used widely inscience, industry and agriculture today. Whenradioactive phosphorous, for example, is mixed witha chemical fertilizer the radioactive substance can betraced through the plant as it grows.

tritium Often called hydrogen three. Extra heavyhydrogen whose nucleu8 contains two neutrons andone proton. It is three times as heavy as ordinaryhydrogen and is radioactive.

unstable All radioactive elements are unstable sincethey emit particles and decay to form other elements.

uranium A heavy metal. The two principal isotopesof natural uranium are Trr- and U. 1r6 has theonly readily fissionable nucleus which occurs in ap-preciable quantities in nature, hence its importanceas nuclear fuel. Only 1 part in 140 of natural ura-nium is U.

Van de Graaff accelerator An electrostatic genera-tora particle accelerator. To obtain the voltage,static electricity is picked up at one end of the ma-

101 Atomic Terms and What They Mean 63

chine by a rubber belt and carried to the other endwhere it is stored.

X-ray RIghly penetrating radiation similar to gammarays. Unlike gamma rays, X-rays do not come fromthe nucleus of the atom but from the surroundingelectrons. They are produced by electron bombard-

went. When these rays pass through an object theygive a shadow picture of the denser portions.

"Z" Symbol for atomic number. An element's atomicnumber is the same as the number of protons foundin one of its nuclei. All isotopes of a given elementhave the same "Z" number.

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Appendix B

Quantities of some commonly used radioisotopes required to equal either 500 or 10 milli-curies arranged according to their half-life.'

Isotope Half-lifeQuantity 9 required to equal:

500 millicuries 10 millicuries

Argon 41 109 minutes 0.01 micrograms 0.0002 micrograms.Potassium 42 12.4 hours 0.08 micrograms .0016 micrograms.Sodium 24_ 15.1 hours 0.06 micrograms .01E2 micrograms.Gold 198 2.7 days 2.05 micrograms .041 micrograms.Iodine 131 8.1 days 4.1 micrograms .082 micrograms.Phosphorus 32 14.3 days 1.75 micrograms .035 micrograms.Chromium 51 27.8 days 0.55 micrograms .011 micrograms.Iron 59 45 days 10.2 micrograms .204 micrograms.Strontium 89 53 days 18 micrograms .36 micrograms.Iridium 192 74 days 5.5 micrograms .11 micrograms.Sulphur 35 87 days 11.5 micrograms 0.23 micrograms.Polonium 210 138 days 111.5 micrograms 2.23 micrograms.Calcium 45 163 days 27 micrograms 0.54 micrograms.Zinc 65 250 days 65 micrograms 1.30 micrograms.Iron 55 2.9 years 222 micrograms 4.43 micrograms.Cobalt 60 5.3 years 440 micrograms 8.80 micrograms.Krypton 85 10.3 years 5.2 milligrams 25 micrograms.Hydrogen 3 12.5 years 0.05 milligrams 1 microgram.Ctrontium 90 25 years 3.15 milligrams 63 micrograms.Cesium 137 30 years 5.75 micrograms 115 micrograms.Radium 226 1,620 years 0.5 grain 10 milligrams.Carbon 14 5,800 years 0.x2 gram 2.3 milligrams.Plutonium 239 24,000 years 8.0 gvame4 oz.) 160 milligrams.Uranium 235 7.1X 108 years 525 ros 10.5 lbs.Uranium 238 4.5X 109 years 3,300 lbs 66 lbs.Thorium 232 1.4X let. years 5 tons. 200 lbs.

I These weights are for the pure radioisotope. In practice, the activematerial is generally mixed or alloyed with a quantity of inactive materialand may constitute only a small fraction of the bulk. Also, self or in-ternal shielding may reduce the external radiation considerably.

2 108 etc. is merely shorthand for expressing large numbers-in thiscase 100,000,000 (eight ciphers)-so that 7.1 X10710,000,000 years.

3 One gram equals 0.035 ounces avd. (approx. 1 /78th of an ounce).A milligram equals 0.000035 ounces (35 millionths of an ounce).A microgram equals 0.000000035 ounces (35 billionths of an ounce).

GAMMA RADIATION LEVEL AT THREE FEET FROM 1 CURIE OF CERTAIN RADIOISOTOPESRIHr

Sodium 24 2. 31 Iridium 192 0. 61Gold 198.. 30 Cobalt 60 1. 59Iodine 131 28 Zinc 65 . 36Iron 59 77 Cesium 137 .43

64

BIBLIOGRAPHY

The following publications are availablefrom the Superintendent of Documents, Gov-ernment Printing Office, Washington 25, D.C.:Handbook No. 42.S.s.sz HANDLING OF RADIOACTIVE

ISOTOPES, price $0.20.Handbook No. 48.CONTROL AND REMOVAL OF RADIO-

ACTIVE CONTAMINATION IN LABORATORIES, price $0.15.

Handbook No. 51.-RADIOLOGICAL MONITORING METHODSAND INSTRUMENTS, price $0.20.

Handbook No. 52.MAXIMUM PERMISSIBLE AMOUNTSOF RADIOISOTOPES IN THE HUMAN BODY AND rarAxi-MUM PERMISSIBLE CONCENTRATIvNS IN AIR ANDWATER, price $0.25.

Handbook No. 54.PROTECTION AGAINST RADIATIONSFROM RADIUM COBALT 60, AND CESIUM 137, price $0.25.

Handbook No. 55.PROTECT' ON AGAINST BETATRON-SYNCHROTRON RADIATIONS UP TO 100 MILLION ELEC-TRON VOLTS. price $0.25.

Handbook No. 50.-SAFE HANDLING OF CADAVERS CON-TAINING RADIOACTIVE ISOTOPES, price $0.15.

Handbook No. 58.-RADIOACTIVE-WASTE DISPOSAL INTHE OCEAN, price $0.20.

Handbook No. 59. PERMISSIBLE DOSE FROM EXTERNALSOURCES OF IONIZING R..DL&TION, price $0.30.

Handbook No. 61. REGULATION OF RADIATION EX-POSURE BY LEGISLATIVE MEANS, price $0.25.

RADIATION HAZARDS IN FIREFIGHTING, price $0.35.

RADIATION SAFETY AND MAJOR ACTIVITIES IN THE*TOMIC ENERGY PROGRAMS, jULY-DECEMBER 1956,price $1.25.

SOME EFFECTS OF IONIZING RADIATION OE HUMAN BE-mos, price $1.25.

AO,

HANDBOOK OF FEDERAL REGULATIONS APPLYING TOTRANSPORTATION OF RADIOACTIVE MATERIALS, price$0.25.

RADIATION SAFETY PRIMER, price $0.25.

The following pvblications are available fromthe Office of Technical Services, U.S. Depart-ment of Commerce, Washington 25, D.C.:A SUMMARY OF ACCIDENTS AND INCIDENTS INVOLVING

RADIATION IN ATOMIC ENERGY ACTIVITIES, JUNE 1945THROUGH DECEMBER 1955, price $0.45.

A SUMMARY OF ACCIDENTS AND INCIDENTS INVOLVINGRADIATION IN ATOMIC ANERGY ACTIVITIES, JANUARY1956 THROUGH DECEMBER 1950, price $1.00.

The following publications are available fromthe Safety & Fire Protection Branch, USAEC,Washington 25, D.C.:RADIATION SAFETY PRIMER INSTRUCTORS HANDBOOK,

single copies only, no charge.

The following publications are available inlimited quantities from the Division of Licens-ing and Regulation, USAEC, Washington 25,D.C.TITLE 20, CODE OF FEDERAL REGULATIONS, ALL PARTS.

An excellent source of basic data is "SelectedMaterials on Employee Radiation Hazards andWorkmen's Compensation" published February1959 by the Joint Committee on Atomic Energy,Congress of the United States. For sale bySuperintendent of Documents, price $1.00.

It U. S. GOVERNMENT PRINTING OFFICE : 1970 0 - 404-850

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