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DOCUREIT RESUME ED 055 807 SE 012 072 AUTHOR Kastner, Jacob TITLE Nature's Invisible Rays, World of the Atom Series. INSTITUTION Atomic Energy Commission, Oak Ridge, Tenn. Div. of Technical Information. pUB DATE 70 NOTE 50p. AVAILABLE PROM USAEC, P. O. Box 62, Oak Ridge, Tennessee 37830 (Free) EDRS PRICE MF-$0.65 HC-$3.29 DESCRIPTORS *Atomic Theory; *Instructional Materials; Measurement Techniques; *Radiation; *Radioisotopes; Reading Materials; Resource Materials; *Secondary School Science ABSTRACT This booklet is one in the "World of the Atom Series" for junior high school students and their teachers. It describes the sources, methods for detection, and useful applications of the invisible radiation that occurs naturally on earth. Numerous photographs are included throughout the text. (PR)

ED 055 807 Nature's Invisible Rays, World of the Atom Series. … · DOCUREIT RESUME ED 055 807 SE 012 072 AUTHOR Kastner, Jacob TITLE Nature's Invisible Rays, World of the Atom Series

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Page 1: ED 055 807 Nature's Invisible Rays, World of the Atom Series. … · DOCUREIT RESUME ED 055 807 SE 012 072 AUTHOR Kastner, Jacob TITLE Nature's Invisible Rays, World of the Atom Series

DOCUREIT RESUME

ED 055 807 SE 012 072

AUTHOR Kastner, JacobTITLE Nature's Invisible Rays, World of the Atom Series.INSTITUTION Atomic Energy Commission, Oak Ridge, Tenn. Div. of

Technical Information.pUB DATE 70NOTE 50p.AVAILABLE PROM USAEC, P. O. Box 62, Oak Ridge, Tennessee 37830

(Free)

EDRS PRICE MF-$0.65 HC-$3.29DESCRIPTORS *Atomic Theory; *Instructional Materials; Measurement

Techniques; *Radiation; *Radioisotopes; ReadingMaterials; Resource Materials; *Secondary SchoolScience

ABSTRACTThis booklet is one in the "World of the Atom Series"

for junior high school students and their teachers. It describes thesources, methods for detection, and useful applications of theinvisible radiation that occurs naturally on earth. Numerousphotographs are included throughout the text. (PR)

Page 2: ED 055 807 Nature's Invisible Rays, World of the Atom Series. … · DOCUREIT RESUME ED 055 807 SE 012 072 AUTHOR Kastner, Jacob TITLE Nature's Invisible Rays, World of the Atom Series

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Page 3: ED 055 807 Nature's Invisible Rays, World of the Atom Series. … · DOCUREIT RESUME ED 055 807 SE 012 072 AUTHOR Kastner, Jacob TITLE Nature's Invisible Rays, World of the Atom Series

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Page 4: ED 055 807 Nature's Invisible Rays, World of the Atom Series. … · DOCUREIT RESUME ED 055 807 SE 012 072 AUTHOR Kastner, Jacob TITLE Nature's Invisible Rays, World of the Atom Series

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The Author

Jacob Kastner received his Ph.D. in physics from the University ofToronto and has specialized for many years in radiation and radio-activity research. He was formerly a research physicist for the NationalResearch Council of Canada and for the General Electric Company, andwas director of research for the Picker X-Ray Corporation. He is nowsenior physicist in the Radiological Physics Division at ArgonneNational Laboratory in Illinois. Dr. Kastner is conducting research onmeasurement of background radiation levels in Lake Michigan andelsewhere, and on the effects of plant growth and seasons on naturalradioactivity.

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CONTENTS

WE'RE ALL IN THE SAME BOAT! ... - 1

There's More to the Sun Than Meets the Eye . 5Brazil Nuts and Cereals 9Clear, Cool Water 11

WHO CARES AND WHY? 13What Harm Can It Do? 13How Much Is Too Much? 14Who Wants to Know? 15

HOW CAN YOU TELL? 23Radiation Doesn't Tickle But Fortunately

It Takes an Awfully Good Picture 23Experiments Are Fun 26

FROM MINE TO MOON 32You Can Get Away From It All 32Up, Up, and Away 33The World's Biggest Belt

Earth's Magnetic Personality 34Acsop's Bullies 34What's Up, Doc? Green Cheese? 36Moon's Pearly Light? ....... 39

RELAX AND ENJOY IT 41What We Don't Know Could Fill a Book 41You Can't Get Away From It 41

READING LIST 43

United States Atomic Energy CommissionDivision of Technical Information

Lawary of Congress Catalog Card Number: 70-6069551970

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Natures Invisible Rays4 jacod _Xasbzer

WE'RE ALL IN THE SAME BOAT!

The scientists in the little boat have nofishing poles but they still hope to catchsomethingan occasional glimpse of nature'sinvisible rays! Of course, if they're invisiblewe can't glimpse them but at least we canobserve their tracks, provided we're cleverenough to build the proper detector.

The old saying, "He's so thick-skinned hedoesn't know when he's being insulted", hasapplied to living things since their existenceon this earth. In addition to visible light,plants and animals have always been exposedto invisible penetrating rays.* These couldand did damage the living cells by strippingelectrons from the cells' atoms, that is,converting them to ions, and thus interferingwith the cells' normal functions.

Now right here I'm going to come to ascreeching stop and start explaining a fewthings. Many occupations have their ownlanguage, as anyone knows who tries totranslate a doctor's prescription! So if you'regoing to understand and enjoy what I'm goingto tell you about what's going on around us,I'd better do some translating.

*A collective nonn for rays is radiation-

Scientists measuringcosmic rays on LakeMichigan. (See thechapter "ExperimentsAre Fun" that begins onpage 26.)

1

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What areelectrons? We know that atomsjoin toeether to form molecules. They oftenstick together very tightly and require outsideenergy to force them apart. When atomschange from a looser to a tighter arrangement,they dye off energy in the form of heat,electricity, etc. For example. when coal isburned, carbon unites with oxygen to formcarbon dioxide and heat. The reverse is alsotrue, of course. When atoms are to beseparated from each other, energy from theoutside is needed to do the job.

How are atoms attached to each other?What are their bonds? The answer comes fromelectricity.

For centuries man has known that whenamber is rubbed with a cloth it becomeselectrically charzed and can pick up bits ofstraw or paper. The Creek word for amber iselektron and if a substance is repelled by thecharged amber it is negatively charged: ifattracted it is positively charged.

Static electricity and flowing electricity(current) are both forms of electrons, ornegatiNely charged particles. When the elec-trons are stationary, or static, they are at-tached to the atom. These can be pulled off,leaving the atom positively charged: some-times the atom acquires extra electrons andthen becomes negatively charged_ When theatoms join to form a molecule, they shareelectrons. Living cells are made up of suchmolecules.

Let's go back to the atom. If we describethe electron as a bit of negative electricity,the rest of the atom must be positive to keepit from flying away. The hydrogen atom isour simplest atom and its positive nucleus iscalled a proton. The diagram shows thecomparison between gravitational and elec-trical attraction_

Other atoms, such as oxygen, are moreintricate since they are made up of more

2

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-

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Earth Electron

protons and electrons (equal numbers) in eachcase_ The number of protons in the nucleusdetermines the kind of chemical element wehave: for example, oxygen has 8 protons. andnitrogen, 7 _

To make life a little more complicated.the nuclei of most atoms also contain someextra weight in the form of neutral particlescalled, amazingly enough. neutrons_ Twoatoms of the same chemical family (havingthe same number of protons) are calledisotopes if they only differ by how "fat"(heavy) they are, that is, by how manyneutrons they have in their nuclei_ The nameisotope comes from the Greek isos meaningsame and topos meaning place (or the sameplace in the chemical table of elements).

Electron

Electron Electron

A helhan atom (left) and a hydrogen atom_

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LITHIUMAtomic Number -3Atomic Weight-6 or 73 Electrons3 Protons3 or 4 Neutrons

Isotopet are GrIOMS ofan element distinguish-able by their weight.

LITH UMAtomic Number-3Atomic Weight-83 Electrons3 Protons5 Neutrons

Some atoms are so heavy, they get "ex-cited enough" to lose weight suddenly.* Theycan do this in many ways: and you also haveto remember that. 'as Einstein stated, matter(which has weight) and raw energy are reallyinterchangeable. Thus, many atoms in theirexcitement will give off rays consisting ofparticles of matter and/or bundles of energy.

Such unstable atoms are called radiationactive or radioactive. The bundles of rawenergy are called photons.i- When the photonscome from the nucleus we call themgamma rays: when they result from a re-arrangement of the outside electrons, they'recalled X rays. This is like worrying about aman's originis he English or Australian? Itdoesn't really matter: his behavior is whatcounts.

The invisible ionizing radiation. which hasbeen part of the environment of plants andanimals over millions of years, is made up ofjust such particies of matter or bundles ofenergy.

*Eac.h chemical element has one or a few pre-ferred atomic arrangements of protons, electrons, andneutrons. These stable isotopes contain an equalnumber of protons and electrons and the same or asomewhat greater number of neutrons. Atoms withan excess of protons or neutrons are said to be in an"excited" or unstable state and undergo suddencbangias to preferred isotopic arrangements.

t A photon is often called a quantum (littlepackage) of radiation. It behaves more like a cloud ofenergy than a ball of matter. X rays or gamma raysare high-energy, short-waveIength electromagnetic ra-diation (photons). Only when such photons areemitted by a nucleus are they called gamma rays.More generally, X rays may result when an excitedorbital electron loses its energy or when a chargedparticle suffers sudden change in speed.

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Atm can be benaberdsd sada'atomic particks and itsmew bed mind gam isslew redtectire

Its interference with these living cells hasgenerally been so small that it has not beennoticed- It is only within the last 100 yearsthat man realized that life on earth wascontinually being bombarded_

This little book has been written to giveyou an idea of the kind and amount of thisradiation, where it comes from, how wemeasure it, and why we investigate it, espe-cially since it has been ignored for most ofman's existence_

There's More to the Sun Than Meets the EyeThe girl in the picture is getting more than

she bargained for in the form of externalradiation exposure_ Bedes the ultravioletphotons from which she hopes to develop atan (an effect inside the skin), she is beingbombarded by even more penetrating radia-tion, both from the earth and from outer

41 I

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A,Light radiations Heat radiationscan be seen can be felt

Radiations from radioactivematerials cannot be-

space. She can't feel it because there are nonerve endings deep within her body. Further-more, there are few lasting effects since thebody is pretty good at repairing this minorinternal damage, which might be comparedwith a tiny sunburn.

Most of the earth's background radiationconsists of gamma rays or X rays, which resultmainly from the radioactive decay of unstablepotassium,* thorium, uranium, and otherradioactive elements in the soil. These ele-

Heard where. There may even be disadvantages inSeen ments are found in minerals nearly every-

Felt having a brick and concrete or granite home.Dr. William Spiers of Leeds, England, one of

?Smelled the world's foremost experts on natural radia-Tasted tion, points out that the intensity of

gamma rays from radium in the brick mayprovide as much as three times the exposureone might expect from a wooden house.

These levels of exposure are 50 to 100times less than that which is considered quitesafe for man. There are certain areas on theworld's surface, such as in Brazil or India,where the very low safety limits set by ourgovernment experts are actually exceeded_

*Natural potassium, ffice many other elements, isan elemental family composed of several members(isotopes), which have different weights. In this case afat isotope, 4 0K, iS the unstable one and occasionallyleaves the family after giving up a piece of itself (abeta particle) to become part of another family, thecalcium family.

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X rays from these minerals, led HenriBecquerel to the discovery of natural radio-activity in 1896.* He had been investigating acertain salt of uranium that, as he had shownsome years earlier, glowed brilliantly underthe action of ultraviolet light. A bit of thissalt, after exposure to light, was wrapped inblack paper and placed near a "sandwich"consisting of a sheet of silver and a photo-graphic plate. Becquerel found, by accident,that the photographic plate was affected, orfogged, regardless of whether the salt hadbeen exposed to light He concluded thaturanium produced penetrating radiation simi-lar to that discovered by Wilhelm Roentgent ayear before. Roentgen had generated X rays tartificially by directing electrons into ametallic target.

Following Becquerel's discovery it wassoon determined that the atoms of such heavymetals as uranium or thorium are constantly,though very slowly, breaking down and givingoff alpha rays§ and 1,e:a rays,1 as well asX rays in the process.

That part of our external exposure whichcomes horn outer space can be traced to the

*Becquerel won a Nobel Prize in Physics in 1903for discovering radioactivity in uranium.

tRoentgen won the Nobel Prize in Physics in1901 for discovering the X ray.

tX rays that are machine produced are properlycalled "Roentgen rays".

§Alpha rays c7-e streams of alpha particles, whichare positively charged and consist of 2 neutrons and2 protons (really a helium nucleus). Alpha radiation isthe least penetrating of the three commoft forms ofradiation (alpha, beta, and gamma). It is so weak thatit can be stopped by a sheet of paper, and it isdangerous onlywhen inhaled or swallowed.

¶Beta rays are streams of beta particles, which areidentical with electrons when negative, and whenpositive are called positrons.

vwftle'

Henri BecquereL

Wilhelm Roentgen.

7

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Cosmic-ray research isoften conducted at highaltitudes such as at thePic du Midi Observa-tory in the HighPyrenees in France.

This Cockcroft-Waltongenerator provides theffra stage of particleacceleration for an ac-celerator, or atomsmasher, at the Ar-gonne National Labora-tory in Illinois.

PARTICLEOR RAY

ALPHA OWE NE=

BETA 1=GAMMA

PAPER WOOD CONCRETE

..11M .1110

Alpha, beta, and gamma penetrations.

steady rain of charged particles (cosmic rays)moving at nearly the speed of light andfalling upon our planet at all times and fromall directions. These particles are just the

, nuclei of ordinary atoms stripped of theirelectrons; they are for the most part thenuclei of hydrogen atoms (protons).

The property of cosmic rays that setsthem apart from all other kinds of radiationand accounts for the extraordinary role theyhave played in the.; development of modernphysics is the very large individual eneres oftheir particles. Before their discovery, thehighest energy particles known were thosegiven off in the natural decay of radioactiveatoms.

Now why are physicists interested in suchhigh-energy particles? Because they have thecapability of smashing atomic nuclei into bits.The hope is that man, by studying the detailsof the crash, may understand the forces thathold the nucleus together. In fact, beforeman-made machines* were developed, scien-tists were looking at the pieces of the collisionof cosmic rays with oxygen and nitrogennuclei in our atmosphere. This naturallyoccurring debris accounts for most of the

*Such a machine is the 200 billion electron volt(Bev) particle accelerator being built in Batavia,Illinois. There are 10 accelerators in this country and17 in foreign countries with energies greater than1 Bev.

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radiation exposure of our sunbathing younglady. A large part of this radiation consists ofphotons (electromagnetic radiation), cover-ing a fairly large spread of energies, and asmall but important part are high-energyneutrons.*

These neutrons crash into molecules ofour atmosphere until all the particles have thesame energy, which is the same as saying thatthey end up at the same temperature. At thisslow speed they are easily captured by ni-trogen atoms to form radioactive carbon(carbon-14) or super-heavy radioactive hy-drogen, called tritium (3 .The breakdownor disintegration of the-se isotopes contributeslittle to the external exposure because theirradiation is not penetrating. However, ingaseous form these materials can be swal-lowed or inhaled and, like alcohol or tobacco,can be dangerous if taken in large quantities.This brings us to the unavoidable problem ofthe intake of radioactivity from food anddrink.

Brazil Nuts and CerealsWhenever scientists bring up the question

of internal exposure due to natural radio-activity in food they immediately think ofJ3razil. Not only because of the very high

*Neutrons are uncharged particles with massslightly greater than that of a proton. The isolatedneutron is unstable and decays with a half-life ofabout 13 minutes into an electron and a proton.Neutrons sustain the fission chain reaction in anuclear reactor. Half-life is the time in which half theatoms in a radioactive substance disintegrate toanother nuclear form.

-I-Nitrogen-14 captures a neutron to becomenitrogen-15, which, in a relatively short time, ejects aproton to become carbon-14. Some , of the heavynitrogen atoms break up into tritium and other lightatoms.

vt 13

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10

gamma-ray activity of the soil, which exists incertain areas of Brazil as well as India, butalso because of the Brazil nut with its very1iigh radioactivityabout 14,000 times thatof common fruits. Of course the Brazil nut isexceptional and by no means characteristic ofnuts in general_ Cereals are also relativelyhighperhaps as much as 500-600 times thatof fruits, which have the lowest concentra-tions of natural radioactivity. The table pointsout pretty clearly that it pays to keep awayfrom rich foods for more than one reason_

RELATIVE ALPHA ACTIVITY OF FOODSFood Stuff Relative Activity

Brazil nuts 1400Cereals 60Teas 40Liver and Icidney 15Flours 14Peanuts and peanut

butter 12Chocolates 8Biscuits 2Milks (evaporated) 1-2Fish 1-2Cheeses and eggs 0-9Vegetables 0_7Meats 0_5Fruits 0_1

Actually the table discusses only the alphaactivity of foods and this tells nothing aboutthe radioactive potassium contribution_ Allmuscle-building foods contain potassium, andwe must eat to live. Recent surveys indicatethat for most populations the radioactivepotassium in our muscles provides 10-20times the internal exposure of any of theother radioactive materials, such as radium,carbon-14, or tritium, which are retained inthe body_

Whenever scientists are concerned withthe internal exposure to man from radio-activity retained in his body, they also have tostudy the human food chain_ They need to

14-

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M.

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follow the way in which the earth's radio-active chemicals are absorbed into plants andanimals, which, in turn, are eaten by humans.This mechanism provides for depositing, dis-tributing, and removing the chemicals in ourorgans. It has been found, just as in the caseof Brazil nuts, that many plants and animalsretain certain chemicals to a greater degreethan others, and in this way develop a specificpathway for a particular radioactive elementto get into the human body.

For example, radium is found in differentconcentrations throughout the human foodchain. Studies have been made in a greatnumber of mammalsmice, rats, rabbits,dogs, pigs, and man. Approximately 1 to 10%of the radium taken in is retained, mainly inthe skeleton and a small amount in cartilageand thyroid.

A very clear transfer was that of radio-active lead, which concentrated in the organsof arctic caribou. These animals serve as thebasic diet of some Eskimos whose bones werefound to contain high concentrations of thiselement.

Clear, Cool Water

With the exception of some of my friendswho claim it rusts pipes, most people believethat there is virtue in clear, cool water. Thereis also something else in well water. A studyin progress in the midwest began with thediscovery, 20 years ago, of the high naturalradioactivity in the drinking water of severalmunicipal water supplies. In 1955 the radio-activity was found to come from radium,which had been dissolved out of the soil alongwith the other more common salts, such ascalcium, magnesium, etc.

The deep wells of Joliet, Illinois, forexample, have 300 times more radium than

15 ti

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Chicago's lake water. Eventually analyseswere carried out all over the country.

The water from the wells of Maine has3000 times as much radium as the PotomacRiver, which serves Washington, D. C., ourcapital. Of course, Maine's radioactivity ismild indeed when compared with that ofsome springs in Kansas and Colorado, orJachymov, Czechoslovakia, where the con-centration is 10,000 times greater.

Amazingly enough it has been less than 50years since such quantities of radium in waterwere considered a oreat asset. Radium andthorium were used as medicines for all sortsof diseases. Fortunately it only took a genera-tion for most doctors to realize that radiumchemically resembles natural calcium so muchthat it tends to pile up in our bones and doserious damage. However, there are still placesin the world that offer the advantages ofbathing in radioactive mineral springs. Severalyears ago, I ordered mineral water in Milanand noticed that the label on the bottleboasted about the radioactive contents andthe merits of such radioactivity in curingmany gruesome illnesses.

Advertisement for radium medi-cines in the early 1900s_

12

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WHO CARES AND WHY?A quick answer to this question is that

scientists want to know and therefore care,and medical doctors and hygienists* need tocare. However, before discussing why thesegroups care about radiation, let me explainbriefly that it is important to know thequality and quantity of the radiation to whichman is exposed because of the damage thatradiation can do to biological matter.

What Harm Can It Do?In general, radiation damages the complex

molecules within a cell, and interferes withthe cell's chemical machinery to the point, inextreme cases, of killing it_ The delicatestmcture of the genest is particularly vulner-able to the impact of radiation. A cell that isnot killed may be so damaged that it cannotduplicate itself, that is, undergo mitosis.

If a cell is of a type that normally doesn'tdivide, the destruction of the mitosis ma-chinery isn't fatal to the whole organism. Thefruit fly Drosophila, which, as an adult, hasvery few cell divisions occurring in its ordi-nary body cells, can survive radiation doses ahundred times greater than that needed to killa man.

In humans, however, there are manytissues whose cells must undergo divisionthroughout life. Hair and fingernails growbecause of cell division at their roots- Theouter layers of skin are steadily lost through

*Persons who deal with the establishment andmaintenance of health in an individual or group.

Genes are hereditary units, contained in eachbody cell, which determine the characteristics of anunborn child. Genetic effects of radiation are thosethat can be transferred from parent to offspring.Somatic effects of radiation affect only the exposedindividual.

17

AllEr

Hermann J. Miller wona Nobel Prize for show-ing that nzdiation cancause mutations inDrosophila.

13

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14

rubbing and are replaced through constantcell division in the deeper layers. The same istrue of the linings of the mouth, throat,stomach, and intestines. Blood cells are alsocontinually breaking up and Faust be replaced.

How Much Is Too Much?If radiation kills the mechanism of divi-

sion in only some of these cells, it is possiblethat those that remain intact can divide andeventually replace or do the work of thosethat can no longer divide. In that case theradiation damage is relatively mild and even-tually disappears.

Sometimes the radiation is so weak thatthe damaged cell can still divide, but it hasbeen so changed, or mutated, that the cell andits descendants no longer function normallyin the body_ It is in this way that radiationmay cause skin cancer, leukemia, and otherdiseases. It is this type of bodily, or somatic,cell damage that may arise from the naturalradiation background; although the prob-ability, Ince the background's strength, isextremely low.

Mutations can be produced in the sex cellstoo. Since these cells are passed on fromparent to child, succeeding generations areaffected and not merely the parent. Actually,where sex cells are concerned, the relativelymild effect of mutations is more serious thanthe drastic one of nondivision. A fertilizedovum that can't divide eventually dies anddoes no harm; one that can divide but isaltered may subsequently give rise to adefective child.

That is why scientists maintain that thereis no threshold* in the genetic effect of

*A threshold is an amount of radiation belowwhich there is no effect. A threshold dose is thesmallest amount of radiation that will produce aneffect.

11, 18

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radiation and no "safe" amount of radiation,insofar as genetic effects are concerned. How-ever small the quandty of radiation absorbed,mankind must deal with a correspondingincrease in the genetic load.* Although thedamage may not be apparent, once a sex cell'sstructure is altered by radiation (or any otheragent), it has a better chance of unfavorablyaffecting some as yet unborn person_

Background radiation accounts for muchless than 1% of the spontaneous mutationsthat take place naturally. The others arise outof chemical effects, random heat (molecularvibration)t effects, and so on_ In the light ofthe relatively small effects resulting from ournatural radiation environment, let us nowexplore the motivation of those key groupsthat were mentioned earlier.

Who Wants to Know?Scientists want to know both for the sake

of knowing and for the helpful applicationsthat the knowledge can provide. Much of theinformation about natural radiation comesfrom investigations that were completelyunconcerned with human environmental ques-tions. For example, Dr_ Henry Faul, a geo-physicist at the University of Pennsylvania,points out that it would be difficult todiscover why anyone needs to know theanswers to such questions as "How old is arock?", "How old is man?", and "How old isthe earth?". Yet they have been asked overand over again since the dawn of humansociety.

liThis is the buzden of unwanted genes that eachanimal has_

t When molecules vibrate because they are warmor hot, there is always the possiloility of a wildmovement of the atoms that results in the breaking ofa chemical bond.

19

Nuclear techniqueswere used to determinethe 2,000,000-year ageof this early ancestor ofman. Zinlicnthropus isthe name given to thisskull, which %SUS dis-covered in Africa in1959.

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Oceanographers bringaboard a 50-gallon sea-water sampler from theocean depths as part oftheir research of radio-activity in the sea.

Ws Been a Long Time

The only reliable method of measuringsuch very long periods of time is based on thisdiscovery by Pierre and Marie Curie in 1898:Some atoms are radioactive, that is, theychange naturally into other atoms at regularand constant rates. We call the original radio-active atoms parent atoms, and the atomsthey disintegrate into daughter atoms. Whenwe compare the populations of parent atomsto daughter atoms and perhaps even great-grandparents to great-granddaughters for verylong-lived elements Ince uranium,* we canmake a pretty good estimate of say, the age ofthe earth, which is 4.5 billion years.

How Fast (Slow) Is the Ocean's Bottom Piling Up?

Radioactive beryllium-10 (1° Be) with ahalf-life of 2.7 million years is produced bycosmic rays and has been detected in marinedeposits. From this activity scientists deducedthat some of the ocean bottom formed fromdissolved chemicals in the seawater at a rateof about 2 millimeters (a little less than 118inch) per million years!

the Age of ManIf we want to determine the age of man,

we look for a natural radioactive material thatdecays at a much faster rate. When we find apiece of wood in some ancient structure, wecan measure the amount of carbon in it. Wedetermine how much of it is carbon-14 (14C),half of whose atoms decay every 6000 years.We then calculate back to the time when theradioactivity from the 4 C was the same as itis now in living wood (where it is continuallybeing replenished from the atmosphere).

*Most of its atoms live for billions of years.

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Who Got There First?

With the aid of I 4 C it has been possible todate human living sites from many points inthe western United States. The rust appear-ance of these sites, about 11,500 years ago,apparently occurred at a time when a landbridge was open from Asia to America overwhat is now the Bering Strait. An ice-freepassage extended from this bridge throughpresent-day Alaska and western Canada to theUnited States. This may have been the routetaken by the first immigrants to America;these were mammoth-hunters, who made thecharacteristic flint aovis arrow and spearpoints.

..1611111M1.-

A Clovis arrow point chipped from frmt by the earliest men on theAmerican continent. The photograph is actual size.

About 11,000 years ago, the Clovis peo-ple had spread across the area of theUnited States and into Mexico. They mayhave been the ones who killed most of themammoths and then gradually assumed thecharacteristics of the Folsom culture- TheFolsom people were bison-hunters, and for along time were thought to have been the firstinhabitants in America_ With 14( it finallywas possible to place these two cultures inproper orderthe Clovis firstand to asso-ciate them with major natural changes, es-pecially the advance and retreat of glaciersacross the continent.

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The tendency to de-posit fat seems to beinherited, and breedingstock with low fat con-tent can be selected,using muscle-seekingpotassium-40 to showthe proportion of mus-cle in each potentialparent. Above a steer isplaced in a whole bodycounter.

How Old Is that Imported Liquor?When your dad offers that expensive

imported liquor to his guests, he can be surehe wasn't cheated about its age. The U. S.Treasury Department maintains a sensitiveanalytical laboratory tohat can measure thealcohol's minute amount of radioactive hydro-gen (tritiumhalf of whose atoms break upevery 12 years). The customs duty paid bythe importer is related to the age of theliquor.

0Beginning 1 Half-life 2 Half-lives 3 Half-lives 4 Half-lives

of life 12 Years 24 Years 36 Years 48 Years

Radioactive decay pattern of hydrogen-3 (tritium).Half-life is the time in which half the atoms in aradioactive substance change to another form.

That's Not Muscle, That's Fat!Biological scientists and medical practi-

tioners alike have used the body's naturalradioisotopes to help them learn abouthumans and animals in a nondestructive way.As mentioned before, muscle contains a lot ofpotassium where fat tissue has none.Potassium-40 (4° K), a radioactive potassiumisotope, emits gamma rzys that are so pene-trating they can pass t.hrough a 250-poundathlete or even a cow.

An important medical application is therelationship of muscle-fat ratios in humanswith disease. Highly sensitive whole bodydetectors in rooms with thick iron walls (tocut out the earth's gamma rays) are nowavailable in most of the major biological

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institutions and hospitals of the world. Themeat industry has even carried out somepreliminary experiments to establish the pos-sibility of purchasing cattle on the basis ofmuscle-fat ratios determined in this way.Maybe someday we'll see such iron rooms setup in every stockyard!

Scientists will seize upon any source ofinformation to further their knowledge. Thuseven man's bad habits are used in this way. Itrecently has been shown that cigarette smokecontains a naturally occurring radioactiveelement, polonium-210. Studies have demon-strated that more of this radioelement isfound in the lung and other soft tissues ofcigarette smokers than those of nonsmokers.

Still another technique is based on thetiny amounts of radium remaining in thebones of humans who were exposed toradium poisoning before its hazards weregenerally understood.

;

se

444

ek

4111._t*:-

This girl in the chute ofa large whole bodycounter has lust had thenatural radioactivity inher body counted_

_

Dogs about to be examined in a whole body counter_

Er amples of such people are the men andwomen in the U. S. and Switzerland whopainted watch dials with radium paint, which

23

w r

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made the dials glow in the dark. (Theseworkers often used their lips to keep a I-mepoint on their brushes.) The bones of thesevictims are an important source of informa-tion on bone growth as well as on the effectof radium on human bone.

&

_

Radium-dial painters in a watch factory in 1922_ A st all theseemployees have been identified, and the living ones participated in astudy at Argonne National Laboratory to determine how much radiumhad accumulated in their bodies_

The time it takes to build up bone cellsand to reabsorb them is an important clue tothe process of bone growth. It is possible toestimate this turnover time of human bone bymeasuring the fraction of a bone section stilllabeled with radium even as much as 40 yearsafter it was acquired.

Doctors and hygienists have to know whathappens in nature before they can judgewhat's really harmful. Only by knowing theamounts and variations of natural radio-activity can such people make intelligentinterpretations of the data they get in theirwork.Health Physics

Before a nuclear-powered electricity gen-erating facility is constructed on a site, themanagement usually calls in radiation safetyofficers (called health physicists in theUnited States) to make measurements of the

"-

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natural background and to identify the typesof radioactivity present. This then provides athreshold or base against which to checkfuture plant operations. Thus, if the plant'sdischarge (effluent) cooling water is foundto contain more radioactivity or other iso-topes than that present in the intake from thelocal stream, prompt measures can be takento improve the purification technique. Ofcourse, the local public health people mightinsist that the water coming out of the plantbe cleaner than when it went in.

This, for example, is the situation in aGerman Westphalian Nuclear Research Estab-lishment near the Rhine River. The Rhine isso filthy that fish have trouble living in it. Inrecent years a white whale lost its way fromthe North Sea and was sighted upstream inthe Rhine River. Even though it was an airbreather, the poor thing was having greatdifficulty keeping its blowhole free of themuck from the river. Nevertheless, the ef-fluent water - from Westphalian reactors isamazingly free of contaminants.

Another factor that is of great concern toradiation safety people is the possibility ofdischarging radioactivity into the air. Thegeneral method used in sampling the atmo-sphere is to draw air through a filter at aknown rate for a known period of time. Thefilter radioactivity is then measured. Theproblem in this simple technique is that thereare days when the air is heavy with thedaughters of the radioactive gas, radon; theconcentrations of their natural and short-livedradioisotopes can be as much as 500 times themaximum permissible concentration of thelong-lived isotopes in the nuclear fuel, whichshould not be allowed to escape from thenuclear plant.

So you see the need for the _publichygienist to know "what comes naturally"; hecan then carry out the proper detective work.

25

Network of towa-s onthe Atomic EnergyCommission reservationnew- Richland, Wash-ington, used by atmo-spheric physicists inmeasuring quantity,concentration, and dilu-tion of radioactive ma-terials in the atmo-sphere_

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Medicine

Medical doctors today depend a great dealon the use of artificial radioactive materials asaids in diagnosing or pinpointing illnesses. Forexample, radioactive iodine, 1 3 1 TI behaveschemically in the body just Lae its non-radioactive isotope, iodine-127_ The penetrat-ing gamma rays of the 1311 permit observa-tion from outside the body with some formof radiation detector. The thyroid gland,located at the base of the neck, controls theway in which our body converts food toenergy. It is also very efficient in trappingiodine from the blood stream. So a doctorwill give a person, suspected of having thyroidtrouble, a drink containing a tiny amount ofthe radioactive tracer 1 3 1 I and then measurehow much of it is retained by the person'sthyroid_

For tracer experiments such as these it isoften necessary to know the natural in-visible rays that might hide what one islooking for.

Measuring radioiodine uptake r'n the thyroid gland with extremely smallamounts of a mixture of iodine-131 and iodine-I25. On the left is asmall television set that is mounted in such a -may that good viewingrequires that the head be kept i n the desired position. On the right isanother view of the child in position for thyroid uptake study.

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HOW CAN YOU TELL?

This question is particularly suitable forthe presence of nature's radiation because it isso small_ This is the same question you wouldask a fine primitive hunter if he told you thata leopard had just passed down the trail andthat the leopard had injured its right frontpaw. The leopard's path, like radiation, canonly be detected by its spoor. Spoor (or spur)comes from the Saxon word for track. Ger-man scientists still refer in this way to thetracks developed in photographic film afterthe passage of nuclear radiation.

When the numbers of rays are as small asis generally the case in nature, the trailbecomes very difficult_ One must either wait along time and build up evidence or set a verysensitive trap that will be triggered to give analarm.. In the following section we will outlinesome of the ways that can and have been usedto count and test the strength of the elusiveradiations to which we are continually ex-posed_ We will also describe some ingeniousexperiments_Radiation Doesn't Tickle But FortunatelyIt Takes an Awfully Good Picture*

Very shortly after Becquerel's discoveryof radioactivity using a chunk of uranium anda photographic plate, Roentgen used gelatinemulsion, or film, to photograph X rays andthereby make "radiograms". (Incidentally, incorrect scientific language a photograph is thecamera and the resultant picture is a photo-gram. Compare with telegraph and telegram.)

*At least not at these levels_ Dr_ Norman Frigerio,a radiobiologist at the Argonne National Laboratoryin Illinois, suggests that some people can detect anintense source by a tingling of the skin_

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Lord Ernest Ruther-forcL

24

The history of radiation detectors hasfollowed the history of physics. Ever since itsdiscovery, studies of radiation effects onmatter have been made. At first only solidmatter, crystalline particularly, was studied inthe early laboratories_ It -was soon learnedthat the passage of radiation through -certainchemicals, like zinc sulfide (ZnS), would giverise to flashes of light that could be seen withthe naked eye.

Lord Ernest Rutherford* and his studentsspent hours in a darkroom looking into asmall eyepiece coated with ZnS, which hecalled a spinthariscope. They observed andcounted the individual flashes of light(scintillations) resulting from the im-pact of alpha rays. Today we are able toamplify these light flashes electronically andrecord both their number and intensity. Inthis way we can measure the rate of exposurefairly easily, whereas a film emulsion can onlyadd up the radiation over a period of time.

Other solids, crystals, and glasses are alsoable to store radiation energy_ When subjectedto heating or ultraviolet irradiation, thesesolids give off visible light that is a measure ofthe stored radiation energy_ Of course, manydifferent kinds of exposure can cause thesame total light_ One therefore needs addi-tional evidence before being sure it was, touse our comparison, a leopard and not a tigerthat passed down the trail.

An application that is most suitable forsuch solid, luminescent, or light-producingdosimeterst is the evaluation of the natural

*Lord Rutherford received the Nobel Prize inChemistry in 1908 for formulating the theories ofradioactive disintegration of elements, the nature ofalpha particles, and the atom's nucleus.

-I-Dosimeters, or dose measurers, are energy stor-ing solids_

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radiation as related to plant growth.* Theadvantage of such solids is their relativeresistance to weathering, mild temperaturechanges, humidity, etc. Such a study wascarried out recently in which a number ofsuch solids were imbedded in the bark of oaktrees, and every 2 weeks, several dosimeterswould be read to establish whether thebackground rate had changed_ The figureclearly demonstrates the marked break in ratewhen the leaves began to grow on the trees inthe spring.

....... 70

CD 60

2 50-g 400-o 30

15

-a20

10 --

00

rLithium fluoride dosim-eters (left) embedded inthe bark of an oak tree_

INTEGRAL RADIATION DOSAGE IN THE TRUNKOF OAK TREES

4 8 12Weeks

16

Accumulated gamma exposure dose_

This principle of using radioactivity's en-ergy as its own giveaway has been quite usefulin dating old pottery and establishing the ageof layers of the ocean's bottom. We recentlyheated a piece of core drilled from the oceanfloor 2 miles deep in the Pacific, and sureenough it gave off blue light.t The core provedto contain uranium and thorium that hadbeen radiating for 100,000 years.

*Such a study is called radiation ecology-t Blue light is given off as a result of heating a

material that has stored energy. This light is calledthermoluminescence.

29

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As laboratory techniques became moresophiscated and physicists learned how tocreate vacuums, they began to study gases.Some of these experiments were the basis forthe discovery of X rays. Ionization* of a gas isone of the most common and sensitive indi-cators of the passage of radiation. This is thebasis of the well known Geiger counter aswell as the less sensitive but very accurate ionchamber.

A liquid detector that grew out of watch-ing bubbles form in a glass of beer led to aNobel Prize in physics in 1960. Donald A.Glaser, an American physicist, pointed out in1952 that bubbles will form along the trackof a charged particle that has passed through asuperheated liquid_ The high density of theliquid makes it far superior to the old-fashioned cloud chambers that exhibited jet-Ince vapor trails for lazy, slow particles, butwere inefficient for tracking the kangaroo-liketrail of super-energetic radiation.

On the left is a photograph of tracks in abubble chamber, which tells the story of amajor collision. Contrast the size of the tinysolid detectors in the figure on page 27 withArgonne National Laboratory's 12-foot bub-ble chamber. The world's largest, the chamberwill contain 25,000 liters (6500 gallons) ofliquid hydrogen and weigh 3500 tons.

Experiments Are FunThe nosy experiments that we scientists

perform to spy on nature are fun. This isbecause the results not only satisfy ourcuriosity, but the experiments themselvesoften give us an excuse to get outdoors andsneak up on nature in her home territory. Let

*Ionization is the splitting off of electrons from aneutral atom, which is then left positively charged_

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me tell you about some of the experimentswe have carried out and some we are doingright now.

1E1 113L415ie 1 71000:,,kg' 5.441i st"

Solid state detectors (above) and 12-foot bubble chamber (below).

LIOUID HYDROGEN

CAMERA

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When I tried to requisition a small alumi-num boat with an outboard motor, I wasasked whether I also needed a fishing pole andwhat kind of beer I preferred. But why did wewant to go boating on the lake? The answerwas simply to get away from land and its highcontent of gamma-emitting materials. Forseveral decades, efforts have been made toseparate the natural gamma-ray backgroundexposure into earthborn and non-earthbornparts. Thirty feet of water is enough to shieldall the gamma radiation from the earth. Thus,if sensitive measurements are made a mile ortwo from shore over fairly deep water, oneshould discover how much of the gammaradiation comes from outer space.

When the English scientist Dr. WilliamSpiers visited us earlier and learned that wewere using a very sensitive ionization chamberto measure the earth's gamma-ray background(and therefore, willy-nilly, a non-earth contri-bution), he urged me to go "fishing". Need-less to say, I didn't need too much persuasion.The system* is very portable as you cansee in the picture where measurements arebeing carried out with the aid of a "shave-pak"t plugged into a car's cigarette lighter.The men of the U. S. Coast Guard stationedat Lake Michigan were very helpfuL Therewere several complications Ln what wouldotherwise be fairly straightforward mea-Extremely sensitive en- surements. We had to use a small aluminumvironmenral radiarion boat (see picture on page I ) because themeasuring system. gamma rays from the potassium and radiumin the materials of a large painted wooden orsteel ship would overshadow what we were

*Designed and constructed by Dr. F_ Shonka,St. Procopins College, Lisle, Illinois.This is a small vibrating power supply thatconverts the cigarette lighter's direct current intoalternating current for use with an electric shaver.

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trying to measure. Even the radium in theinstrument dials on the bridge of the CoastGuard cutter gave more current than we werelooking for.

The cutter took us and our little boat outon Lake Michigan so far that the air wouldshield us from the gamma-emitting soil. Thus,if we were separated by 10 meters of waterfrom the nearest earth (beneath us), weneeded to have at least 10,000 meters of airbetween us and the shore. (Water is about1000 times as dense as air.)

But what about radon gas carried by theprevailing wind from shore to us? To accountfor this contamination (radon daughters emitgamma rays when they decay), we carried onboard ship several large collapsed balloons.The balloons were each enclosed in a largeglass bottle, about 50 centimeters in diameter,and attached by a simple valve system to thenarrow neck of the bottle. When one of usblew up a balloon, he acted as a pump tocollect a substantial sample of air at the timeand place of our measurements.

These samples were later measured forradon content. (Of course, we had checkedour individual body contribution of radon.)The air was passed over finely divided andvery cold charco z! or carbon that trapped theradon gas, ai.d the aloha particles from thedecaying radon could then be counted.

We were also corrmed about the purityof Lake Michigan water; after all, soluble saltsfrom surface runoff and human wastes do endup in the lake_ We collected 10-gallon samplesof lake water for analysis. Nowadays theanalysis of gamma rays from weak radioactivesources is so sensitive that we were able todetect the presence of debris from the Chi-nese bomb tests! The main contamination inour water was a slight trace of potassium-40

t

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30

together "V it an even smaller trace of bomb-p roduced um-137 .

After correcting our lake measurementsfor the small contributions from the con-taminated air and water, we were able to tellthe world the value of the cosmic-ray compo-nent at 41°N. (53°N. Geomagnetic) and540 feet above sea level. For comparison withpreviously derived values, everyone adjuststheir figures to sea level and the equator.Values calculated in this way will be smallerbecause there is more atmosphere at sea levelto thin out the primary cosmic rays. Further-more, fewer cosmic rays enter the earth at theequator because of the earth's maDletic field,which tends to guide charged particles toeither pole.

The cosmic-ray contribution at Chicago isabout a quarter of the total radiation expo-sure on land. We generally quote the cosmic-ray value as about 4 microroentgens* perhour.

Having measured the gamma-ray andcharged particle components of the cosmicrays, what about the other major product ofcosmic-ray interactions in our atmosphere,namely, neutrons? It was known that therewere much fewer of these than of gamma raysor charged particles. However, each neutron isas heavy as a hydrogen atom and, if energetic,can knock out of place the hydrogen atomsthat make up most of our cells. It became achallenge to try to measure the exact numberand energy distribution of these neutrons,which hit every square centimeter of areaabout once every 2 minutes.

At fust, we carried out our measurementsin the laboratory, but we discovered that

*A roentgen is a unit of radiation that is theamount of gamma rays required to produce 2 billionpairs of ions in 1 cubic centimeter of dry air understandard conditions (0° Centigrade and 1 atmosphereof pressure). 1 p.r/h = 2000 ion prs_ per cc.

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people in a building 200 yards away weregenerating neutrons periodically with an ac-celerator. A few minutes a day of this extracontribution was more than enough to matcha week's background!

With the cooperation of the City ofChicago Water Department we located ourapparatus at one of Chicago's water intakecribs offshore in Lake Michigan. The cribproved to be an ideal location for measure-ments because it is far enough from shore tobe free of terrestrial and artificial radiation.You can see what the detector for "fast"(energetic) neutrons looks like in the picture.

Another type of detector was used tomeasure very slow, thermal, or room tempera-ture neutrons. We made up half-pint canscontaining special photow.apliic emulsionsthat were loaded with the isotope lithium-6(6 Li). This isotope has the property of beingable to capture a thermal neutron and thensplitting into two new atoms, tritium andhelium. The splitting (explosion) shows up inthe film as a small star or blotch, and thesecan be counted. In the picture one of us isremoving a can that has been on the bridge atthe crib for 6 months. Thanks to the U. S.Coast Guard, we could also put some cans onnavigation buoys 7 miles out in the lake.

At this stage of the experiment we arerelatively satisfied with our measurements ofneutron flux or total intensity. But to be sureof distribution we'll need another few years.

35

f

At the water intakecrip, scintillation count-ing equipment for re-cording neutron bom-bardment is adjusted bythe author.

A can containingcosmic-ray detectingmaterials is removedfrom a bridge on thewater intake crib.

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Uranium miners.

32

FROM MINE TO MOON

Of one thing we are sureradiation ofvarious types and quantities is everywhere. Itis only a question of the proper technique todetermine what kind and how much.

Ever since the discovery of radioactivity,it has been obvious that uranium mines wouldbe sources of invisible rays to which theminers would be exposed. Recently, laws havebeen passed that established fairly strict con-trols on their exposure. Sensitive instrumentsspecially designed to estimate the radioactiveconcentration are under development.

One of these is a beanie-type, battery-operated propeller that sucks air through asmall piece of filter paper. The miner wearsthis on his helmet When he's through work-ing for the day, the filter paper is sandwichedwith a piece of plastic for a while. Theradioactive dust on the paper gives off alpharays that bombard the plastic and weaken itso that when soaked in a suitable chemical,such as lye, small, etched pits are formed.These can be counted, either by hand or bymachine, and the number of pits is an indica-tion of how well the mine is being ventilated.

You Can Get Away from It AllNot all mines exhibit a high level of

radioactivity. In fact, quite the contrary.Mines of common table salt are often veryfree of radioactive impurities and deepenough to shield out most of the radiationfrom outer space. Such mines in Ohio andTexas have been used by researchers to doexperiments that require a radiation-freeenvironment. I know a graduate physicsstudent who means it when he says "back tothe salt niines".

A delicate experiment to determine thestability of the proton was carried out 2 miles

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below the earth's surface in a gold mine inSouth Africa. So far, it has been establishedthat if the proton is unstable at all, its averagelifetime is almost a billion billion billionyears.

Up, Up, and Away

As man rises out of the mines and leavesthe earth's surface he leaves the earth'sradiation but is more exposed to impactsfrom space sources, since he no longer has thebenefit of the shielding of the earth's atmo-sphere. This winter we were fortunate to flyour apparatus on a DC6 at 20,000 feet aboveMiami. The U. S. Department of Commerce'sEnvironmental Science Services Administra-tion (ESSA) has Weather Bureau planes thathave been used for a decade to spot andfollow hurricanes. We obtained, in 6 hours offlying at this altitude, as much data as in2 weeks on the ground!

The question arises: What will be theexposure to the crew and passengers of theproposed supersonic transport that may fly at70,000-80,000 feet? It doesn't look too badfor an hour's flight under normal conditions.However, during a solar flare the sun spits out

-,,,R,I,C...AtrAf

A scientist launchesballoon that will carryradiation detectionequipment.

a

This 570,000-mile-high solar flare occurred onJune 15, 1958.

3 7.$

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The Coast Guard CutterEast Wind near Gm,n-land on the 1952 VanAllen expedition.

34

an intense burst of protons. Furthermore, theearth's magnetic field is distorted so thatmore of these charged particles can arrive atthe earth without deflection. Under suchconditions there is a good possibility that thepilot may be required to take evasive actionand drop to 40,000 feet. Otherwise thepassengers will be subjected to as muchradiation in 1 hour as we now receive on theground in a month!

The World's Biggest Belt Earth'sMagnetic Personality

As man keeps going up out of ouratmosphere and into space, he will no longerexperience exposure from earth's radiation.More and more of the radiation will be cleancosmic rays, including some flurries of radia-tion originating on the sun. Some electronsand protons are trapped in the earth's mag-netic field and constitute belts of radiationsurrounding the earth. Professor James A.Van Allen discovered these belts in 1958when he sent up some Geiger counters byrocket as part of the Explorer 1 satellite.Later it was determined that these belts beginabout 500 miles above the earth's equator andextend out about 40,000 miles.

Aesop's BulliesOne of Aesop's delightful fables tells of

the argument between the sun and the windas to who was the stronger. The test becameone of determining who could make a mantake off his coat. Of course the sun's warmpersonality won over the wind's gruff bruteforce. Well, Aesop wasn't aware that the sunand the wind are one and the same bully outin space. The sun's wind consists of powerfulinvisible rays that wash the earth and moonand swirl millions of miles around and pastthe planets. In this case it's the earth's

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During the suminers of 1952-1955, James A. Van Allen and a researchgroup from the University of Iowa launched instruments high into polarskies to measure low-energy cosmic rays deflected into the auroralregions by the earth's magnetic field. They did this by ruing a small,-ocket from a high-altitude balloon, which had risen to 60,000 feet.The rocket, fired upward through the balloon and using the atmospherebelow as a launch pad, could easily reach 50 miles. On the left aboveare James A. Van Allen (right) and the rocket, which vtows carried highaloft by a balloon. On the right above are a rocket and balloonascending from the East Wind. Below is Van Allen's famous map of theradiation belts derived from the GM tubes carried by Explorer 4 andPioneer 3 satellites.

7r ;ik

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at,_Ampa

Pioneer 6, a deep-spaceprobe now in orbitaround the sun. Fromsuch an orbit it' canradio back informationabout solar radiation.

One of 6 astromonks,brought to the LosAlamos Scientific Lab-oratory in New Mexicofor space radiation en-vironment experiments,is unloaded from a*

plane by an animalpsycho t.

36

magnetic personality that protects most of itsatmosphere from a lot of needless exposure.

In space, of course, there is no blanket ofatmosphere to shield man from direct bom-bardment. We will have to provide him withhis own radiation shield. The uncertaintiesconcerning the intensity and kind of radiationexposure will need to be eliminated before wecan provide the proper protection for a manremaining in space. Much of the incidentradiation energy is dissipated in shieldingmatefial by ionizationthe electrons in theshields carry away the energy harmlessly.

Good spacecraft radiation shields Musttherefore have a lot of electrons in a pound.The best element for this purpose is hydro-gen, which has almost twice as many electronsper kilog.a.m as do all the other elements.Thus, weight for weight, it's a better shield.Since hydrogen will remain a liquid in thecold of outer space (and is also a rocket fuelcomponent), perhaps we shall see our space-ships with double walls containing liquidhydrogen somewhat like inside-out thermosbottles.

What's Up, Doc? Green Cheese?

Now, what happens when we arrive at themoon? Radiation conditions there ought tobe similar to those experienced by our super-sonic transport planes near the top of ouratmosphere. Cosmic rays will come barrellingin from space (with no atmosphere to shieldthe astronaut), smash into the moon's soil,and generate neutrons near the surface, whichwill come boiling back out to pester the poorhumans who have the gall to settle on thesurface. There is one important difference,however, between the top of our atmosphereand the moon's topsoil. There is no nitrogento gobble up thermal neutrons (and generate

t.t. 40

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ike

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38

4C). Thus the flux or internity of thermalneutrons could very well be very much higherthan on 'earth. Since thermal or very slowneutrons are easily captured by stable ele-ments, making them radioactive, this environ-ment may prove a real hazard to spacemen,who wish to stay on the moon for any lengthof time. Their clothes may need to be linedwith lithium or boron. These elements arevery opaque to slow neutrons. At this writingwe have not yet had a final interpretation ofthe information resulting from the Apollo-11or -12 moon landings.

An additional but less important contribu-tion to man's radiation environment on themoon is the lunar radioactivity. Lilce thradioactivity from the earth, it comes aboutmainly from basalt and &ranite reons con-taining potassium, thorium, and uranium. Thelunar soil composition was established in apreliminary way by the Russian experimentson their Luna-I 0 satellite, which orbited themoon in March 1966.

Since then, of course, man has managedthe colossal achievement of bringing backsamples of the moon's surface. These werechecked for their gamma-ray emission in aspecially designed radon-free room, 15 metersbelow the ground. As a result of thesemeasurements, we now know that the concen-tration of thorium and uranium in thesemoon samples is much hice that of similarrock on earth. The radioactive potassiumconcentration, however, proved to be muchlower in the lunar surface material than forearth rocks or even meteorites. Furthermore,there were definite amounts of radioactivealuminum, sodium, scandium, and otherradioactive elements, which are not naturallypresent on earth.

Their presence on the moon is explainableon the basis that the lunar surface material

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has been exposed to cosmic radiation fel.' atleast several million years, thus generatingthese unusual radioisotopes, which are onlyartificially available on earth.

Moon's Pearly Light?An interesting sidelight to the moon's

continual bombardment by radiation fromspace is the very reasonable suggestion byscientists of the Westinghouse Electric Corpo-ration that the energy stored during bombard-ment on the night (and cold) side of themoon is released by the sun's rapid heating inthe form of visible light.

It is well known that many imperfect andimpure crystalline materials, such as quartz orfluorite, will trap (in impurity centels*) theelectrons resulting from ionizing radiation andlater, when heated rapidly, release these elec-trons to recombine with ions and producelight. The light intensity is directly related tothe total radiation exposure. This phenome-non is called thermoluminescence. It is thebasis for a modern system of radiation do-simetry or exposure measurement, which hasbegun to replace the conventional film badgefor radiation safety.

The Westinghouse scientists now estimatethat the moon's thermoluminescent intensitymay amount to as much as one-third of thereflected sunlight in the same region!

A thrilling prospect for a very practicalapplication of the natural lunar radiationbackground is the possibility of using theenergy trapped in the moon's soil during thelunar night_ Moon settlers migbt well tap avast storehouse of energy on the dark side ofthe moon_ By the end of the lunar night, thebombarded material possesses 6 kilowatt

*An impurity center is usually a foreign atom notbasic to the crystalfor example, a trace of iron inquartz or a trace of manganese in fluorite.

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hours per pound more energy than is storedin coal. The dust could be fed into aninsulated chamber to generate heat for a lunarbase or tc produce electricity by heating athermoelzctric generator.

AAP'

+10MMIL

Thermoluminescence from the moon's surface occurs fit the thnvnregion as the sun's rays warm up the meteorite rock, releasingenericv trapped from the solar wind during the lunar night. Above,a meteorite glows with thermoluminescent light after being irradiatedin a laboratory and subjected to temperature changes simulatingconditions on the moon's ace at dawn.

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RELAX AND ENJOY IT

I started this little story by saying that lifeon this planet has always been exposed toradiation. In fact, it is said that it is the veryexistence of radiation that has produced theevolution of the myriad species we havetoday. It is certainly true that changes causedby radiation, which have become involved innatural selective forces, have developed menand animals especially fitted for survival intheir environments.

The academic question always arises: Willgenetic damage by radiation alter man? As wedon't know, and there really isn't much wecan do about it anyway, let's hope thechanges, if any, will be for the better.Goodness knows we can certainly bear to beimproved. The point is that, with the additionof sheer knowledge, man has the imaginationto eventually control his environment.

What We Don't Know Coi Id Fill a BookWhat we don't know is always infmitely

more than what we know. All we can begin totalk about are experiments in the immediatefuture. As we do them and gain more knowl-edge, new frontiers open up-

You Can't Get Away From ItWe are continually being washed by neu-

trinos from the sun- Neutrinos are almostweightless neutral particles, which penetratematter so easily that the intensity of neu-trinos on the night side of the earth isestimated to be only 10% less than the sunside. A very complek and sophisticated appa-ratus has been devised to detect these elusive"critters" but a great deal still needs doing.

Elaborate experiments have been plannedunder the Himalayas to gain the advantage of

41 1,-t, kr- 45

woo 0

Brookhaven NationalLaboratory's solar neu-trino detector is located4850 feet undepgroundin the Homestake GoldMine in Lead, SouthDakota.

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a mountain as an absorber. One experimentactually will consist of a 30-foot cubical roomcontaining a scintillating liquid* and elec-tronic light converters, which will be liketelevision picture tubes 3 feet in diameter.These detectors will be serviced by frogmen!However, we need to know more about thiswash of neutrinos; who knowsthey mayprovide a communication system through theearth that won't depend on the weather orbooster stations!

To know is satisfying, but learning toknow is fun, and designing experiments to pindown information is even more fun than justlearning. When you can leave the lab andinvestigate the world around you what morecan you ask?

*A scintillating liquid detects the light flashescaused by radiation strilcing certain materials.

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READING LTST

Atoms and Molecules, Irving and Ruth Adler, TheJohn Day Company, Inc., New York, 1966, 48 pp.,S2.68. Grades 3-6.

Basic Laws of Matter (revised edition), Harrie S. W.Massey and Arthur R. Quinton, Herald Books,Bronxville, New York, 1965, 178 pp., $3.75.Grades 7-9.

Experiments with Atomics (revised edition). Nel-son F. Beeler and Franklyn M. Branley, CrowellCollier and Macmillan, New York, 1965, 160 pp.,$3.50. Grades 5-8.

Inside the Atorn (revised edition) Isaac Asimov,Abelard-Schuman, Ltd., New York, 1966, 197 pp.,$4.00. Grades 7-10.

Secret of the Mysterious Rays: Tlz, Discovery ofNuclear Energy, Vivian Grey, Basic Books, Inc.,New York, 1966, 120 pp., $3.95. Grades 48.

An electron micrograph of a moon rock.

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1 Mrs. William Spiers5 Argonne National Laboratory AINTLI (bottom)7 New York Public Library m8 Observatoire du Pic du Midi middle); ANL (bottom)10 From Proceedings of the ...S-06,nd United Nations

International Con erence-' on the Peaceful Usesof Atomic Eneigy, September 1 13, 1958,Geneva, Switzerland

12 ANL13 Indiana University15 Des Bartlett, Armand Denis Productions16 E. R. Baylor, Woods Hole Oceanographic Institution17 University of Arizona18 Cornell University (bottom)19 Los Alamos Scientific Laboratory (LASL)20 Dr. Charles E. Miller21 Pacific:Northwest Lzbdratcry24 .-: From Discovery of the Elements; Mary. Elvira Weeks,

Chemical Education PubliShini:Company 1956ANL,Lawrence RadiationANL

nion Carbide Co

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Printed in the United States of America

,USAEC Division of Technical Information Extension, Oak Ridge, Tennessee

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U. S. ATOMIC ENERGY COMMISSIONDivision of Technical Intormation

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