THE REGULATION AND USE OF RADIOISOTOPES IN TODAY'S … · nuclear medicine procedures. The nuclear reactors that produce radioisotopes bombard atoms with high-energy neutrons. The

OOOO OOU.S. Nuclear Regulatory

Commission

THE REGULATIONAND USE OF

RADIOISOTOPES INTODAY'S WORLD

The regulation and use of radioisotopes in today’s world

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IntroductionMore than 100 years ago, scientistsdiscovered that many elements com-monly found on earth occur in differ-ent atomic configurations. These vary-ing configurations, called isotopes,were found to have identical electroni-cally charged particles and identicalchemical properties, but differentatomic weights and physical properties.

It was soon discovered that some iso-topes of elements were radioactive.The dense central portion (called thenucleus) of an atom of the elementemits energy in several different forms.Radioisotopes are simply atoms withnuclei that are seeking a more stablenuclear configuration by emitting ra-diation. Scientists have learned thatmore radioisotopes could be created bysubjecting certain elements to radiationinside a nuclear reactor or bombard-ing them using a particle accelerator.

Gradually we have learned to harnessthese radioisotopes for use in our mod-ern, high-tech world. In this brochureare described some of the most com-mon uses for radioisotopes, as well asthe relative benefits and hazards in-volved in their applications. The ap-pendix at the end of this brochure de-scribes various uses of radioisotopesin this country.


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INSIDE THE ATOM

Pro

ton

s …are the nucleuswhich consists ofprotons, which carrypositive electriccharges…

Neu

tro

ns

Ele

ctro

ns

…and neutrons,which carry noelectric charge.

Encircling thenucleus are electronswhich carry negativeelectric charges.

Also explained are theproperties of radiationthat enable it to changethe physical character-istics of certain materi-als. Because they emittell-tale ionizing radia-tion, extremely smallquantities of radio-isotopes can be traced

and measured using special equipment.This property makes them a usefuldiagnostic tool in medicine. Theradiation from some radioisotopes canpenetrate thick metal parts and providea way to “see” inside objects that areimpenetrable to light. Radiationdeposits sufficient energy in humantissue to disrupt normal cell function asit passes through, thus providinga unique method of attacking anddestroying cancerous cells and tumors.Radiation can also be used to kill bac-teria and germs that contaminate medi-cal instruments and some foodstuffs.

Finally, this brochure describes the re-sponsibilities of the U.S. NuclearRegulatory Commission (NRC), someother Federal agencies, and the States,in regulating the manufacture, use, andpossession of radioactive materials.


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Alpha

Beta

Medical x-ray

Gamma

Neutron

Paper Wood Concrete

A few radioisotopes occur naturally butmost are man made. A radioisotope istypically described by its name fol-lowed by a number, such as carbon-14(C-14) or fluorine-18 (F-18). Thenumber represents the atomic weightor the total number of protons and neu-trons that make up the atom’s nucleus.

Radioisotopes have unique propertiesthat make them useful tools in solvingproblems.

Three predominant types of radiationare emitted by radioisotopes: (1) alphaparticles, (2) beta particles, and(3) gamma rays. The different typesof radiation can penetrate materials ofvarying thicknesses such as paper,body tissue, or concrete. A single sheetof paper will stop an alpha particle,which, becauseit is heavy, hasvery little pen-etrating power.Alpha emittersare typicallyused in smokedetectors. A thinsheet of metalwill stop a betaparticle, which,

1. Radioisotopes emitdifferent kinds ofradiation.

Why AreRadioisotopesUseful?

Penetrating powerof radiation


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2. The length of a

radioisotope’s life

is predictable.

because it is lighter, is more penetrat-ing than an alpha particle. Beta emit-ters such as strontium-90 (Sr-90) areused in the treatment of eye disease.Gamma rays, which have no chargeor weight, can be extremely energeticand highly penetrating. Several metersof concrete or several millimeters ofother dense materials, such as lead, areneeded to block gamma rays. Radio-isotopes that emit gamma rays are usedfrequently in medical applicationsagainst tumors, and in industry to checkfor cracks or flaws in valves and pip-ing. Because of their varying penetrat-ing properties, radioisotopes can bemanipulated to perform different tasks.

The process of radioactive decay, inwhich radioisotopes lose their radio-activity over time, is measured in half-lives. A half-life of a radioactive ma-terial is the time it takes one-half ofthe atoms of the radioisotope to decayby emitting radiation. The half-life ofa radioisotope can range from fractionsof a second (radon-220) to millions ofyears (thorium-232). When radio-isotopes are used in industry or medi-cine, it is vital to know how rapidlythey disappear, so that the preciseamount of radioisotope available forthe medical procedure or industrial useis known.


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3. Radioisotopes of achemical elementbehave in the samemanner as a stable,nonradioactiveelement.

We can trace the movement of a chemi-cal element by using a radioisotope ofthat element. For instance, the chemi-cal element iodine concentrates natu-rally in the thyroid. By using a radio-active isotope of iodine as a tracer, apicture can be taken of the material’spath through the body and its depositin a specific organ.

One Half-Life

Four Half-Lives

Six Half-Lives

Ten Half-Lives

After one half-life only half theradioactivity remains.

After ten half-lives only one thousandthof the radioactivity remains.

Half-life decay


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Radioisotopes come from threesources: (1) from nature, such asradon in the air or radium in the soil;(2) from machine-produced nuclearinteractions in devices, such as linearaccelerators and cyclotrons; or(3) from nuclear reactors.

A linear accelerator is a long, straighttube in which charged particles gainenergy through oscillating electromag-netic fields. A cyclotron is an accelera-tor in which charged particles travel inan almost circular path, rather than in astraight path as in a linear accelerator.Radioisotopes produced in linear ac-celerators are used in some modernnuclear medicine procedures.

The nuclear reactors that produceradioisotopes bombard atoms withhigh-energy neutrons. The research re-actors used for this purpose do not pro-duce electricity and are much smallerin size and power than large power re-actors. Reasearch reactors are mostlyused for training and for identifying thecomposition of certain elements.Forty-seven research reactors arelicensed by the NRC to operate in theUnited States. They are located mostlyat large universities.

Because of the potentially hazardousproperties of radioisotopes, their usemust be closely regulated to ensure thatpublic health and safety are protected.

Where DoRadioisotopesCome From and WhoRegulates Their Use?


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What Is the Roleof the NuclearRegulatoryCommission?

The licensing and regulation of radio-isotopes in the United States are sharedby the NRC, the U.S. EnvironmentalProtection Agency (EPA), and manyState governments. The EPA is alsoresponsible for, among other things,setting air emission and drinkingwater standards for radionuclides. TheStates regulate radioactive substancesthat occur naturally or are produced bymachines, such as linear accelerators orcyclotrons. The Food and Drug Admin-istration (FDA) regulates the manufac-ture and use of linear accelerators; theStates regulate their operation.

The NRC is the Federal agency giventhe task of protecting public health andsafety and the environment with regardto the safe use of nuclear materials.Among its many responsibilities, theNRC regulates medical, academic, andindustrial uses of nuclear materials gen-erated by or from a nuclear reactor.Through a comprehensive inspectionand enforcement program, theNRC ensures that these facilitiesoperate in compliance with strictsafety standards.

The NRC has relinquished itsauthority to regulate certainradioactive materials, includingsome radioisotopes, to most ofthe States. These States, whichhave entered into an agreement as-suming this regulatory authority from


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the NRC, are called AgreementStates, and are shown on the map be-low. Agreement States, like the NRC,regulate reactor-produced radioiso-topes within their borders and mustprovide at least as much health andsafety protection as the NRC.

The NRC maintains approximately6,000 licenses for the use of radio-active materials, and the AgreementStates maintain approximately 16,000

Map of Agreement States

Agreement State

MACT RI

MENHVT

NY

PANJ

OH

MDDE

VAW

MI

IN

KYNC

TN

IL

SC

GAAL

FL

MS

MO

A

TX

OK

KS

LA

IANE

WI

MNND

SD

WY

MT

CO

NMAZ

CA

NV

UT

IDOR

WA

Source: Nuclear Regulatory Commission


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materials licenses. Every license speci-fies the type, quantity, and locationof radioactive material that may bepossessed and used. When radioactivematerial is transported, special pack-aging and labeling are required. Alsospecified in each license are the train-ing and qualification of workers usingthe materials, specific procedures forusing the materials, and any specialsafety precautions required. Every li-censee is inspected periodically eitherby the NRC or the Agreement State toensure that radioactive materials arebeing used and transported safely. Vio-lators of regulatory requirements aresubject to fines and other enforcementactions, including loss of license.


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About one-third of all patients admit-ted to U.S. hospitals are diagnosed ortreated using radioisotopes. Most ma-jor hospitals have specific departmentsdedicated to radiation medicine. In all,about 112 million nuclear medicine orradiation therapy procedures are per-formed annually, with the vast major-ity used in diagnoses. Radioactive ma-terials used as a diagnostic tool canidentify the status of a disease and mini-mize the need for surgery, reducing therisks from postoperative infection.

Radioisotopes give doctors the abilityto “look” inside the body and observesoft tissues and organs, in a mannersimilar to the way x-rays provide im-ages of bones. Radioisotopes carriedin the blood also allow doctors to de-tect clogged arteries or check the func-tioning of the circulatory system.Some chemical compounds concen-trate naturally in specific organs or tis-sues in the body. For example, iodinecollects in the thyroid while variouscompounds of technetium-99m*

(Tc-99m) collect in the bones, heart,and other organs. Taking advantageof this proclivity, doctors can useradioisotopes of these elements astracers. A radioactive tracer is chemi-cally attached to a compound that will

DiagnosticApplications

*The “m” refers to “metastate,” which pertainsto the isotope’s short half-life and elevatedenergy state.

How AreRadioisotopesUsed in Medicine?


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Gamma camera used todetect dysfunctional activityin body organs

concentrate naturally in an or-gan or tissue so that a picturecan be taken. The process ofattaching a radioisotope to achemical compound is calledlabeling.

To detect problems withina body organ, doctors useradiopharmaceuticals orradioactive drugs. Radio-isotopes that have short half-lives are preferred for use inthese drugs to minimize the ra-diation dose to the patient. Inmost cases, these short-livedradioisotopes decay to stableelements within minutes, hours, or days,allowing patients to be released from thehospital in a relatively short time.

The radioisotope used in about 80 per-cent of nuclear diagnostic proceduresis Tc-99m. The penetrating proper-ties of its gamma rays and its short(6-hour) half-life help reduce risk tothe patient from more prolonged ra-diation exposure.

Because of their short half-lives, cer-tain radiopharmaceuticals must be pro-duced, shipped to the hospital, and thenused within a couple of weeks. Short-lived radionuclides such as Tc-99m,gallium-67, and thallium-201 are of-ten used to diagnose the functioning of


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Tracer used in the body of a65-year old man indicatingbone density problems as aresult of a thyroid condition

Photo: Courtesy of Appleton& Lange, from “A ClinicalManual of Nuclear Medi-cine,” by John Walker andDonald Margouless, 1984.

the heart, brain, lung, kidney, or liver.For example, Tc-99m is used to diag-nose osteoporosis, a condition causedby calcium deficiency in older people,especially women.

To evaluate the presence of heart dis-ease, a radioisotope is injected into apatient’s bloodstream while he or sheis exercising on a treadmill. Theradioisotope travels toward the heart,allowing doctors to follow the bloodflow on a screen. While looking at theimage, doctors can check for reducedblood flow through the arteries, a pos-sible signal of heart disease.

Nuclear imaging is also used to evalu-ate brain function. Organic radio-chemicals are labeled with F-18 andthen injected into the bloodstream. Adevice called a gamma camera detectsradiation emitted from the organ, dis-playing an image that can enable thephysician to detect blockages or otherdysfunctional activity.

For some diagnostic tests, the patientneed not come into contact with radio-activity at all. The tests are performedon blood or other fluids taken from thepatient, using a procedure called radio-immunoassay. These tests can detectsome diseases by identifying and mea-suring the amounts of hormones, vita-mins, enzymes, or drugs in the body.


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The same property that makes radia-tion hazardous can also make it use-ful in helping the body heal. Whenliving tissue is exposed to high levelsof radiation, cells can be destroyed ordamaged so they can neither repro-duce nor continue their normal func-tions. For this reason radioisotopes areused in the treatment of cancer (whichamounts to uncontrolled cell division).Although some healthy tissue surround-ing a tumor may be damaged during thetreatment, mostly cancerous tissue canbe targeted for destruction.

A device called a teletherapy unit de-stroys malignant tumors with gammaradiation from a radioisotope such ascobalt-60 (Co-60). Teletherapy unitsuse a high-energy beam of gamma raysto reduce or eradicate tumors deepwithin the body. These units are li-censed by the NRC because they usebyproduct material that is producedonly by a nuclear reactor.

Another treatment, called brachy-therapy, destroys cells by placing theradioisotope (in the form of a sealedsource) directly into the tumor. Gener-ally, two techniques are used for thistype of treatment: (1) direct, manualimplantation of a radiation source by aphysician or (2) automated implanta-tion using a device called a remoteafterloader. The NRC as well as

TherapeuticApplications


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Agreement States li-cense these brachy-therapy devices. Usingthese devices, a small,thin wire or sealedneedle containing radio-active material, such asiridium-192 (Ir-192) oriodine-125 (I-125), isinserted directly into thecancerous tissue. Theradiation from the iso-

tope attacks the tumor as long as thedevice is in place. When the treatmentis complete, long-lived material (Ir-192)is removed, but the short-lived radio-isotopes (I-125) may be left perma-nently. This technique is used fre-quently to treat mouth, breast, lung, anduterine cancer.

Brachytherapy and teletherapy proce-dures are performed only in hospitalsor clinics by trained medical personnel.Strict controls and safety requirementsset by the NRC or the Agreement Statesmust be followed. For example, treat-ment rooms must have adequateshielding to prevent scattered radiationfrom penetrating into an adjacent room.Radiation monitors must be used andpatients carefully observed at all timesduring treatment.

Many types of cancer, such asHodgkin’s disease (cancer of the

Brachytherapy device

Photo: Courtesy of NucletronInternational B.V.


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lymph glands) and cancers of the cer-vix, larynx, and skin, can be treated byradiation alone. Boron capture neutrontherapy has been used on a trial basisrecently to treat potentially fatal braincancer. In this procedure, the diseasedbrain tissue incorporates a neutron-absorbing isotope and then is exposedto neutron radiation originating from anuclear research reactor. The energyand radiation emitted as a result of theneutron activation slow down thegrowth of cancer cells and, in somecases, completely kill them.

The overall objectives of NRC’s safetyrules for radiation medicine are to en-sure that patients receive only the expo-sure medically prescribed and that theradiation is delivered in accordance withthe physician’s instructions.

NRC regulations require that physi-cians and physicists have special train-ing and experience to practiceradiation medicine. The training em-phasizes safe operation of nuclear-related equipment and accuraterecordkeeping.

When using radiation as a medicaltreatment, the physician weighs the po-tential benefits against the risk of sideeffects. Intense radiation exposure of-ten destroys tumors that would provefatal, but side effects such as hair loss,


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How AreRadioisotopesUsed in Industry?

Well-logging device

Detector

Bore hole probe

Shield

reduced white blood cell count, andnausea can be severe and must be moni-tored carefully.

Radioisotopes are used in many oftoday’s industrial processes. High-tech methods that ensure the qualityof manufactured products often relyon radiation generated by radio-isotopes. To determine whether a welldrilled deep into the ground has thepotential for producing oil, geologistsuse nuclear well-logging, a techniquethat employs radiation from a radio-isotope inside the well to detectthe presence of different materials.Radioisotopes are also used to steril-

ize instruments; to findflaws in critical steel partsand welds that go intoautomobiles and modernbuildings; to authenticatevaluable works of art;and to solve crimes byspotting trace elementsof poison, for example.Radioisotopes can alsoeliminate dust from filmand compact discs aswell as static electricity(which may create a firehazard) from can labels.


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Radiation can destroy germs, bacteria,and other harmful organisms that con-taminate medical supplies, blood sup-plies, and even our food. Over theyears, we have learned how to safelytreat these items with radiation to ster-ilize or preserve them when othermethods such as boiling or usingchemical preservatives are either im-practical or not as effective.

Medical supplies, such as rubbergloves, cloth bandages, syringes,and contact lens solution, can besterilized by using an irradiator.An irradiator exposes the materialsto gamma radiation, usually fromCo-60.

Bacteria in foods can be destroyed byusing radiation. Astronauts, for ex-ample, take food into space that oftenhas been preserved using radiation.Food irradiation is discussed in greaterdetail later in this brochure.

The NRC regulates irradiators to pro-tect workers and the public but, withsome exceptions, does not specify thetypes of products that may be irradi-ated. The NRC does not evaluate thequality of irradiated products or the

Irradiation andTreatment of MaterialsWith Radioisotopes


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technical or economic feasibility ofproduct irradiation.

In the United States, food safety isregulated by the FDA and the U.S. De-partment of Agriculture (USDA).

There is an important difference be-tween exposing materials to radiation

An industrial irradiator used for food products consists of a roomwith concrete walls 2 meters thick and a radiation source (Co-60).A conveyor system automatically moves the products into the roomfor irradiation and then removes them. When it is necessary forpersonnel to enter the room, the source is lowered to the bottom ofthe pool, where water absorbs the radiation energy and protectsthe workers.

ConveyorSystem

UnloadingProcessedProduct

Loading

ControlConsole

IrradiationRoom

StoragePool

Radiation Source

Radiation Shield

Diagram: Courtesy ofFood Technology Service, Inc.


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from an irradiator and exposing themto radiation from a reactor. Thegamma radiation from Co-60 in an ir-radiator kills bacteria and germs, butdoes not leave any radioactive residueor cause any of the materials exposedto become radioactive themselves.This is because the Co-60 is containedin stainless steel capsules and does notcommingle with the product being ir-radiated. This differs, however, fromthe effects of neutron radiation. Mate-rial can become radioactive after ex-posure to neutrons from a reactor orlinear accelerator because the neu-trons are absorbed by the nucleus ofthe atoms in the material, which thenform different radioactive isotopes orelements (also referred to as neutronactivation).

In manufacturing, radiation canchange the characteristics of materi-als, often giving them features that arehighly desirable. For example, woodand plastic composites treated withgamma radiation are used for someflooring in high-traffic areas of depart-ment stores, airports, hotels, andchurches, because they resist abrasionand ensure low maintenance. Somegemstones, such as blue topaz, can begiven a more pleasing color using neu-tron radiation treatment.


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Measuring andTesting Applications

Although there might be someresidual radiation from neutronbombardment of gemstones and otherconsumer products, the half-lifeof these materials is generally soshort (seconds or hours) that riskto the public is extremely low. To en-sure that the products are manufac-tured correctly, manufacturers anddistributors of these materials must belicensed by the NRC.

Today, luminous watch dials arepainted with tritium or promethium-147 replacing radium used many yearsago. These radioisotopes trigger achemical reaction with other materialsupon contact, which then give off a“glow.” These materials are sometimesplaced in gun sights or clocks andwatches so they can be used at night.One frequently sees “exit” signs illu-minated by tritium as safety markers onpassenger aircraft, aboard ships, and inmany buildings. Some gas lanternmantles are manufactured with theradioisotope thorium to provide a brightlight when burned.

As radiation from a radioisotope passesthrough matter, it is scattered or ab-sorbed. The amount of radiation pass-ing completely through depends on thethickness and density of the matter. Thisproperty makes radiation useful for manymanufacturing quality control processes.

Gauge, luminous watch dialand smoke detector


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For example, radioisotopes in gaugesare used to monitor and control thethickness of sheet metal, textiles, alu-minum foil, newspaper, copier paper,plastics, and photographic film as theyare manufactured. Radiation penetratesthe material as it is processed, anddetectors measure the amount of radia-tion passing through and compare it tothe amount that should be detected forthe desired thickness of material. If thereadings are too high or too low, con-trols in the manufacturing process canbe activated to correct the problem.This is accomplished with a highdegree of accu-racy, and the ma-terials need notbe touched by hu-man hands.

R a d i o a c t i v etracers can alsobe used in themachine-toolsindustry to mea-sure wear on cut-ting tools anddrills. Gaugesalso play a rolein the measure-ment of every-day objects, suchas the amount ofglue on a post-age stamp, the

The use of portable gaugesis widespread in industriessuch as agriculture andconstruction. In the illustra-tion on the left, the gammasource is placed underneaththe surface of the groundthrough a tube. Radiation isthen transmitted directly tothe detector on the bottomof the gauge, allowing ac-curate measurements ofcompaction.

On the right, the neu-tron source remainsabove the surface, andradiation is emitted intothe ground and scatteredback to the detector toprovide a measurementof the moisture content.

Gauge

Detectors

Radiation

Source

Surface

Depth

Direct transmission

Radiation

Gauge

Detectors

Source

Surface

Backscatter


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level of liquid incanned beverages,the amount of airwhipped into icecream, and theamount of tobaccopacked into a ciga-rette. Other gaugeand nuclear instru-ment applicationsinclude: (1) moni-toring the structural

integrity of roads, buildings, andbridges; (2) exploring for oil, gas, andminerals; and (3) detecting explosivesin luggage at airports. To ensure ad-equate water supplies, radioisotopesare used to measure water runoffsfrom rain and snow, flow rates ofstreams and rivers, and leakage fromlakes, reservoirs, and canals.

Radioisotopes can also be used totest for the presence of certain mate-rials. For example, a small amount ofamericium-241 is found in mostsmoke detectors used in homes andoffices. This radioisotope is part ofthe sensing unit that triggers an alarmwhen smoke is present.

Portable gauge used to testthe structural integrity ofroads and bridges


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Portable radiographycamera used to test forcracks in metal

Industrial RadiographyA process called industrial radiogra-phy is used to inspect many metalparts and welds for defects. A sealedradiation source, usually Ir-192or Co-60, beams radiation at the ob-ject to be checked. Special photo-graphic, or radiographic, film on theopposite side of the source is exposedwhen it is struck by radiation passingthrough — like an x-ray. More radia-tion will pass through if there arecracks, breaks, or other flaws in themetal parts and will be recorded on thefilm. Therefore, structural problemscan be detected by studying the film.

Radiography is used throughoutindustry. For example, jet engineturbine blades are radio-graphed to ensure thatinternal cooling pas-sages are manufacturedproperly.

The NRC or AgreementStates license radi-ographers and periodi-cally inspect them toensure they follow safetyprocedures.


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Radioisotopes have played an impor-tant role in improving agricultural sci-ence. Radioisotopes are used as a re-search tool to develop new strains of

food crops that aremore resistant to dis-ease, are of higherquality, allow earlierripening, and producea higher yield. Wheninsects are sterilizedwith radiation, theymate without produc-ing offspring, thusproviding some con-trol of insect popula-tion growth. With

fewer pests, food crops can flourish.This technique has eliminated screwworm infestation in the southeasternUnited States and Mexico and hashelped control the Mediterranean fruitfly in California. It has also been usedto control mosquitoes and flies through-out the world.

Radioisotope tracers in plant nutrientsenable scientists to make discoveriesthat have increased the effectivenessof fertilizer.

A major factor in successful crop pro-duction is the presence of an adequatewater supply. Nuclear moisture den-sity gauges can monitor the moisture

How AreRadioisotopes Usedin Agriculture?


25

content of soil, helping make the mostefficient use of limited water sources.

The NRC and the Agreement States li-cense byproduct radioactive materi-als used in these agricultural appli-cations in the United States.

Radiation can be used to destroy bac-teria in food and control insect andparasite infestation. Since 1963, theFDA has approved irradiation as amethod to inhibit sprouting and to de-lay ripening in many fresh fruits andvegetables. The FDA has more re-cently approved the use of irradiationto control insects in food, trichina inpork, and bacteria in poultry, spices,and seasonings.

Currently, irradiation is used in theUnited States on very few fooditems; however, some spices are irra-diated. In 1992, the USDA alsoapproved the com-mercial irradiation ofpoultry, and in 1999,approved commercialirradiation of meat.

The FDA has estab-lished regulationscontrolling irradiationof food. Irradiatedfood must clearly

Food Irradiation andIts Safety


26

display the radura logo (a green,flower-like, international symbol for

irradiation) and words such as“treated with radiation.”

Governments in about 37 coun-tries have approved irradiation ofsome 40 foods. In this countryonly one commercial facility is

devoted solely to irradiating foodproducts. It is located in Florida

and licensed by the State. That fa-cility irradiates strawberries and citrusfruits by exposing them to gamma raysfrom a radioactive source. When notin use, the radiation sources are safelystored in a pool of water.

Although it is a relatively new commer-cial process, food irradiation has beenstudied at length for over 40 years.According to the FDA, research to datehas turned up no evidence of adversehealth effects from irradiation of thetreated food. The radiation passesthrough the food leaving no radioactiveresidue. Some concerns have beenraised regarding the chemical changesthat may alter the finished food prod-uct. However, research has shown thatchanges in flavor and texture caused byirradiating food are similar to changesdue to canning or freezing. Studies arecontinuing to ensure that all irradiatedfood is safe to eat.

Radura logo


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Through a method called radiocarbondating, archaeologists can determinewhen formerly living materials werelast alive. This procedure relies on thepresence of C-14, a naturally occurring,long-lived radioisotope present in allliving things.

The ratio of C-14 to C-12 in the atmos-phere has been relatively constantthroughout history. When an animalor plant dies, it stops taking in carbon,and the amount of C-14 in its tissuebegins to decrease through the processof radioactive decay. Comparing theC-14 to C-12 ratio in dead materialwith the “living ratio” enables us to cal-culate how long ago the plant or ani-mal lived. This method was used todetermine the approximate age of twomajor archaeological discoveries in re-cent decades: the Shroud of Turin andthe Dead Sea Scrolls. C-14 analysishas also been used during space mis-sions to test for life on Mars.

Heat generated by radioisotopes isused to power small generators usedfor remote applications, such as inspace exploration.

Radioisotope-powered electrical gen-erators have been used to power ex-ploration space craft, navigational andweather satellites, and communication

Geology, Archeology,and Space

What Are Other Usesof Radioisotopes?


28

satellites. They allowus to operate weatherstations at the Northand South Poles, seis-mic sensing stations

in remote loca-tions, and devicesplaced on theocean floor forscientific investi-gations and na-tional defense.

The Departmentof Energy (DOE)m a n u f a c t u r e sradioactive ther-mal generators,which are poweredby plutonium-238and Sr-90. TheNRC has providedtechnical assis-

tance for some of theseapplications.

A procedure called ac-tivation analysis is frequently usedto identify trace quantities of materi-als such as glass, tape, gunpowder,lead, and poisons that are important tocriminal investigations. Samples of

Silicon-GermaniumThermocouples

Cold Side

Plutonium-238 Fuel

Hot Side

CoolingTubes

CoolingFins

Height: 45 inches Diameter: 18 inches Weight: 123.5 pounds

ow does a radioisotope thermoelectricgenerator (RTG) produce electricity?The “fuel”—a plutonium isotope that

can't explode—“decays,” or loses itsradioactivity, giving off heat. Thatheat is absorbed by a device called athermocouple, which consists ofa compound of two metals—siliconand germanium—that are “doped.”“Doping” the metals—addingimpurities to them—changes theirelectrical and thermal properties.As a result, energy moves from the“hot side” of the thermocouple—the side closer to the fuel—to the“cold side,” producing avoltage. Gas circulatingthrough cooling tubeskeeps the RTG fromgetting too hot, and finsdissipate the heat.

The thermocouple was firstdemonstrated early in the lastcentury, but the efficiency was toolow to be practical. In the 1950s,researchers discovered they couldget higher efficiencies from a thermo-couple by using “semiconduc-tor” materials such as silicon andgermanium. After that, there wasno looking back. Today’s conver-sion efficiency is about 5 percent,but with some of the conversiontechnologies now under develop-ment, tomorrow’s efficiencies areexpected to be at least 20 percent.

Diagram: Courtesy of theNuclear Energy Institute


29

materials are placed in a nuclear reac-tor and bombarded with neutrons. Theinduced radiation produces a “finger-print” of the elements in the sample.

In addition, activation analysis can provethe authenticity of old paintings by de-tecting whether certain modern materi-als are present. Museums routinely usethis and other techniques that rely onradioisotopes to spot forgeries.

Radioisotopes are used to detect pol-lution in the air, water, and soil.Sources of acid rain and greenhousegases that may be causing globalwarming can be traced using radio-isotopes. In addition, electron beamradiation can be used to remove gas-eous pollutants such as sulphur diox-ide or nitrogen oxide, both harmfulgases emitted from coal-fired powerplants and other industries.

When used properly, radioisotopes area productive part of today’s world. TheNRC and the Agreement States remaincommitted to protecting public healthand safety in the use of these nuclearmaterials by inspecting medical, aca-demic, and industrial applications care-fully, and monitoring users to ensuresafe practices.

Conclusion


30

Cesium-137

Used to treat cancerous tumors…tomeasure correct patient dosages ofradioactive pharmaceuticals…tomeasure and control the liquid flowin oil pipelines…to tell researcherswhether oil wells are plugged bysand…and to ensure the right fill levelfor packages of food, drugs and otherproducts. (The products in these pack-ages do not become radioactive.)

Chromium-51

Used in research in red blood cell sur-vival studies

Cobalt-57

Used as a tracer to diagnose perni-cious anemia

Cobalt-60

Used to sterilize surgical in-struments…and to improve the safetyand reliability of industrial fuel oil burn-ers. Used in cancer treatment, food ir-radiation, gauges, and radiography.

Copper-67

When injected with monoclonalantibodies into a cancer patient, helpsthe antibodies bind to and destroy thetumor.

Americum-241

Used in many smoke detectors forhomes and businesses…to measurelevels of toxic lead in dried paintsamples…to ensure uniform thicknessin rolling processes like steel and pa-per production…and to help determinewhere oil wells should be drilled.

Cadmium-109

Used to analyze metal alloys forchecking stock, scrap sorting.

Calcium-47

Important aid to biomedical research-ers studying the cellular functions andbone formation in mammals

Californium-252

Used to inspect airline luggage for hid-den expolsives…to gauge the moisturecontent of soil in the road constructionand building industries…and to mea-sure the moisture of materials storedin soils.

Carbon-14

Major research tool. Helps in researchto ensure that potential new drugs aremetabolized without forming harmfulby-products. Used in biological re-search, agriculture, pollution control,and archeology.

Appendix: Some of the Major Uses ofRadioisotopes in the United States.


31

Iridium-192

Used to test the integrity of pipelinewelds, boilers and aircraft parts andin brachytherapy/tumor irradiation.

Iron-55

Used to analyze electroplating solu-tions and to detect the presence ofsulphur in the air. Used in metabolismresearch.

Krypton-85

Used in indicator lights in appliancessuch as clothes washers and dryers,stereos, and coffeemakers…to gaugethe thickness of thin plastics and sheetmetal, rubber, textiles and paper… andto measure dust and pollutant levels.

Nickel-63

Used to detect explosives, and in volt-age regulators and current surge pro-tectors in electronic devices, and inelectron capture detectors for gaschromatographs.

Phosphorus-32

Used in molecular biology and genet-ics research.

Curium-244

Used in mining to analyze materialexcavated from pits…and slurriesfrom drilling operations.

Gallium-67

Used in medical diagnosis

Iodine-123

Widely used to diagnose thyroid dis-orders and other metabolic disordersincluding brain function.

Iodine-125

Major diagnostic tool used in clinicaltests and to diagnose thyroid disor-ders. Also used in biomedical re-search.

Iodine-129

Used to check some radioactivitycounters in in vitro diagnostic testinglaboratories.

Iodine-131

Used to treat thyroid disorders.(Former President George Bush andMrs. Bush were both successfullytreated for Graves’ disease, a thyroiddisease, with iodine-131.)


32

Phosphorus-33

Used in molecular biology and genet-ics research.

Plutonium-238

Has powered more than 20 NASAspacecraft since 1972.

Polonium-210

Reduces the static charge in produc-tion of photographic film and othermaterials

Promethium-147

Used in electric blanket thermo-stats…and to gauge the thickness ofthin plastics, thin sheet metal, rubber,textile and paper.

Radium-226

Makes lighting rods more effective.

Selenium-75

Used in protein studies in life scienceresearch.

Sodium-24

Used to locate leaks in industrial pipelines…and in oil well studies.

Strontium-85

Used to study bone formation andmetabolism.

Strontium-90

Used in survey meters by schools, themilitary and emergency managementauthorities. Also used in cigarettemanufacturing sensors and medicaltreatment.

Sulphur-35

Used in genetics and molecular biol-ogy research.

Technetium-99m

The most widely used radioactivepharmaceutical for diagnostic studiesin nuclear medicine. Different chemi-cal forms are used for brain, bone,liver, spleen and kidney imaging andalso for blood flow studies.


33

Thallium-201

Used in nuclear medicine for nuclearcardiology and tumor detection.

Thallium-204

Measures the dust and pollutant lev-els on filter paper…and gauges thethickness of plastics, sheet metal, rub-ber, textiles and paper.

Thoriated Tungsten

Used in electric arc welding rods inconstruction, aircraft, petrochemicaland food processing equipment indus-tries. They produce easier starting,greater arc stability and less metalcontamination.

Thorium-229

Helps fluorescent lights last longer.

Thorium-230

Provides coloring and fluorescence incolored glazes and glassware.

Courtesy of Management Information Systems, Inc.

Tritium

Major tool for biomedical research.Used for life science and drug me-tabolism studies to ensure the safetyof potential new drugs…for self-lu-minous aircraft and commercial exitsigns…for luminous dials, gaugesand wrist watches…to produce lumi-nous paint, and for geological pros-pecting and hydrology.

Uranium-234

Used in dental fixtures like crownsand dentures to provide a naturalcolor and brightness.

Uranium-235

Fuel for nuclear power plants andnaval nuclear propulsion systems…and used to produce fluorescentglassware, a variety of colored glazesand wall tiles.

Xenon-133

Used in nuclear medicine for lungventilation and blood flow studies.

Notes

34

NUREG/BR-0217 Rev. 1

APRIL 2000

U.S. Nuclear RegulatoryCommission

Washington, DC 20555-0001

Office of Public Affairs

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THE REGULATION AND USE OF RADIOISOTOPES IN TODAY'S … · nuclear medicine procedures. The nuclear reactors that produce radioisotopes bombard atoms with high-energy neutrons. The