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ED 297 954 SE 049 4'9

TITLE Radioisotopes: Today's Applications.INSTITUTION Department of Energy, Washington, DC. Nuclear Energy

Office.REPORT NO DOE/NE-0089PUB DATE 88

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EDRS PRICE MF01/PCO2 Plus Postage.DESCRIPTORS Atomic Structure; Cancer; College Science; Higher

Education; Industry; *Nuclear Energy; *NuclearTechnology; *Radiation; *Radioisotopes; *Radiology;Science Education; Scientific and TechnicalInformation; *Technological Advancement

ABSTRACTRadioisotopes are useful because of their three

unique characteristics: (1) radiation emission; (2) predictableradioactive lives; and (3) the same chemical properties as thenonradioactive atoms of that element. Researchers are able to "order"a radioisotope with the right radiation, half-life, and chemicalproperty to perform a given task with the knowledge of these threecharacteristics. This publication includes information on the uses ofradioisotopes in medicine for providing doctors with diagnostic andtherapeutic techniques for scanning organs and contributing to thehealing process in the treatment of cancer. Radioisotopes can help toauthenticate works of art and solve crimes. In industry radioisotopesare used to detect hidden flaws in hardware and improve productquality. Uses in agriculture include insect control and thepreservation of foods. (RT)

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Today's Applications

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U.S. Department of EnergyAssistant Secretary for

Nuclear EnergyOffice of Program Support

2

RADIOISOTOPES:TODAY'S APPLICATIONS

In the century since they were firstdiscovered, radioisotopes havetransformed the fields of medicine,science, industry, and agriculture.Radioisotopes have become the powerfuland often subtle tools that researchersnow rely on to probe and unravelnature's most closely guarded secrets.

Doctors look deep into the hiddenrecesses of the human body withoutscalpel or pain, observing the delicatefunctions of internal organs to detectand treat disease in its early stages.Scientists chart the lost chronology ofthe ancient past, precisely dating the eraof delicate fossil fragments and ancientmountain ranges. Manufacturersproduce metal castings that are freefrom flaws and plastics withunprecedented strength. Farmers use lessfertiliz.)r yet grow crops with higheryields to help feed a hungry world.

For more detailed information about the uniquecharacteristics of radioisotopes, open cover flap.

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ABOUT RADIATION ANDRADIOISOTOPES...

Atoms that emit radiation are calledradioactive isotopes or radioisotopes.There are radioisotopes of most of thechemical elements on Earth. Many occurnaturally; many more can be manmade.A radioisotope is designated by a nameand a number. The name is that of thechemical element, and the number is itsatomic weight. For instance, theradioisotope carbon-14 has the samechemical properties as the stable elementcarbon-12 but is heavier by two atomicweight units. The difference in weight, inthis case, makes carbon-14 radioactive.

Radioisotopes have three uniquecharacteristics that make themuseful tools:

Radioisotopes emit radiation.

Radiation, in the form of rays orparticles, can penetrate substances ofvarying thicknesses such as paper, bodytissue, or concrete. The rays, calledgamma rays, can be extremely energeticbut can be stopped by about four feet ofconcrete. The particles, on the otherhand, have less penetrating power. A thinsheet of metal will stop a beta particle,which is really an electron. A single sheetof paper will stop an alpha particle,which is very much larger than abeta particle.

4

Radioisotopes have radioactive livesthat are predictable.

Over time, radioisotopes lose theirradioactivity through the process ofradioactive decay that is measured inhalf-lives. The half-life of a radioactivesubstance is the time it takes for aquantity of that substance to lose one-halfits radioactivity. Half-lives ofradioisotopes range from fractions of asecond to millions of years, but thehalf-life of each radioisotope isprecisely known.

Radioisotopes of a chemical elementhave the same chemical propertiesas the nonradioactive atoms ofthat element.

Radioisotopes are available that have thechemical properties of nearly all theknown chemical elements on Earth,making it possible to trace a chemicalelement by adding a radioisotope ofthat element. Radioisotopes used in thisway are sometimes referred to asradiotracers.

Knowledge of these three characteristicsenables researchers to "order" aradioisotope with just the right radiation,half-life, and chemical property toperform a given task.

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Radiation given off by radioisotopes permits externalcameras to take pictures of internal organs of thebody for medical diagnosis.

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Radiation given off by radioisotopes permits externalcameras to take pictures of internal organs of thebody for medical diagnosis.

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does not concentrate naturally in the organunder study, a radioisotope can bechemically attached to a compound thatwill carry it to the organ so that a picturecan be taken. This process of attaching aradioisotope to a chemical compound iscalled labeling, and the procedure hasgreatly expanded the diagnostic applicationsof radioisotopes.

With technetium-99m, now the mostwidely used radioisotope for diagnosis,doctors examine the brain, heart, blood,lungs, liver, kidneys, thyroid, spleen, andbone. For example, the loss of calcium inolder people, especially women, can lead toweakened bones and a condition calledosteoporosis. To diagnose the condition,doctors can view a patient's skeleton byinjecting technetium-99m into the blood ina chemical form that concentrates in

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the bones. From pictures taken by a sensitive

camera, doctors diagnose the condition of thebones and prescribe treatment. A new method

of diagnosing osteoporosis uses gadolinium-153.This radioisotope emits two soft gamma raysthat differ widely in energy. When thegamma rays are focused on the skeletalstricture, the difference in energy permits

the bone disease to be identified. The method

is called dual photon absorptiometry (DPA).Doctors are currently using two

radioisotopes to diagnose heart disease:

thallium-201 and technetium-99m. Theseradioisotopes are used as blood flowmarkers, allowing doctors to detect the riskof heart disease. Doctors inject one of

GADOLINIUM 153SOURCE ---.......____..

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DUAL PHOTON ABSORPTIOMETRY

The technique of dual photon absorptiometry,which relies on the radioisotope gadolinium-153,enables physicians to make early diagnosis of

osteoporosis.

5 10

the radioisotopes into the patient's bloodduring exercise on a treadmill. Theradioisotope concentrates in the heart,allowing doctors to follow the blood flow.Looking at an image of the heart, doctorscan detect the reduced blood flow throughthe arteries that feed it, which can signalheart disease. Technetium-99m is beingused increasingly because it has a shorterhalf-life than thallium-201 (6 hours asopposed to 72), thus reducing the amountof radiation a patient receives.

Radioisotopes, such as carbon-11 orfluorine-18, provide another method oflooking at internal organs. Theseradioisotopes emit positively charged betaparticles, called positrons, and pairs ofgamma rays traveling in oppositedirections. Two moveable cameras, placedopposite each other, detect the rays andpermit a three-dimensional image to beconstructed by a computer. The technique

Obstruction to blood flow in the heart can bedetected through the use of radioisotopes.

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Heart, Right Ventricle

Pictures of the heart,called angiograms,are used to diagnose Heart, Left Ventricleheart disease. Radio-isotopes such as irridium-191m allow doctors todetermine the condition of the heart. (Courtesy ofBelgian collaborators)

is called positron emission tomography(PET). Because positron emitters haveshort half-lives and must be preparedonsite, PET scans require ready accessto a cyclotron, a special machine forproducing these short-livedradioisotopes. Positron emitters areprepared by irradiating lightelementscarbon, nitrogen, oxygen,fluorineusing the cyclotron. With thehelp of a computer to translate theimages captured by the c,,ameras, bothSPECT and PET are especially valuablein medical diagnosis. Doctors study thecirculatory system and probe theactivities of the brain, adding to ourunderstanding of epilepsy,schizophrenia, Parkinson's disease,strokes, Down's syndrome, andHuntington's chorea.

1 112

Therapeutic Applications

The property of radiation that makes itdangerous also makes it useful in healing.When radiation's energy is deposited inliving tissue, cells can oe damaged ordestroyed. For this very reason,radioisotopes play an important role incancer therapy. Large doses of radiationfocused directly on a cancer can destroy itwith little damage to surrounding tissue.

Doctors rely on three differenttechniques to destroy cancer cells withradioisotopes. One approach involves anexternal machine that destroys the tumorwith gamma radiation from aradioisotope such as cobalt-60. Anotherapproach is to place the radioisotopedirectly into the tumor itself. Aninnovative example of this approach isthe treatment of liver cancer with tinyspheres containing the radioisotopeyttrium-90, which lodge in thecapillaries of the cancerous tissue,providing a localized dose of radiation.A third approach is to use a radioisotopethat naturally concentrates in thediseased organ. This technique is sowidely used to treat many thyroidconditions that it has almost replacedthyroid surgery.

An important advance in the radiationtreatment of cancer involvesradioisotope-labeled monoclonalantibodies. Our bodies naturally produceantibodies that attack foreign matter toeliminate it from the body. Recentadvances in biotechnology have enabledscientists to manufacture artificialantibodies, called monoclonal antibodies.Artificial antibodies can be geneticallyengineered to bind to a type of molecule

11'3 8

The radioisotope yttrium-90 is absorbed into tiny

manmade resin microspheres that are trapped incancerous livers, allowing the short-rangeradiation to destroy nearby cancer cells.

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Surgical supplies and instruments are oftensterilized with radiation from radioisotopes.

found primarily in a cancerous tumor.Labeled with a radioisotope, theantibody can identify or destroy thecancerous tissue. Monoclonal antibodieslabeled with iodine-131 or yttrium-90 arebeginning to show promising results forthe treatment of cancer.

In addition to their importance in thediagnosis and treatment of diseases,radioisotopes play an important role inthe sterilization of medical supplies.Syringes, surgical gloves, andpharmaceuticals like ointments andpowders, which might be damaged byconventional methods of sterilization, areroutinely treated by radiation fromradioisotopes. Other supplies, such aspetri dishes, test tubes, and surgicalinstruments, are also sterilized withradiation.

,,. 1.15 10

RADIOISOTOPES IN SCIENCE

Radioisotopes enable scientists to determinethe age of the Earth and provide achronology of prehistoric times. Radioisotopesare helping us unravel the myseries of ourenvironment, revealing how animal life,

earth, air, and water interact with eachother. Radioisotopes can also be used toauthenticate works of art and even to helpsolve crimes. As flexible scientific tools,radioisotopes help us increase our knowledgeof the world around us.

Geological and ArchaeologicalApplications

Determining the age of the Earth usingradioisotopes has radically alteredprevious concepts of geological history.Early estimates placed the age of theEarth at less than 40 million years. Latercalculations using the radioactive decay ofnatural uranium suggested an age morethan ten times this number. More recentradiological calculations set the age of theEarth at 460 million years.

Archaeologists can also determine datesby a technique known as radiocarbondating. Carbon-I4 is a naturallyoccurring, long-lived radioisotope presentin all living things. The ratio of carbon-I4to carbon-I2 in the atmosphere has beenrelatively constant throughout history.Because living things take in carbon fromthe atmosphere, the ratio of carbon-14 tocarbon-I2 in living things is the same asthat in the atmosphere. When an animalor plant dies, it stops taking in carbon,and the amount of carbon-14 in its tissuebegins to decrease through the process ofradioactive decay. Comparing the

11 ,41 6..

carbon-14-to-carbon-I2 ratio in the deadmaterial with the "living ratio" enables usto calculate how long ago the plant oranimal lived. This comparison permits usto date fossils that are found inarchaeological explorations as belonging toa certain period in history.

Archaeologists collect cane charcoal samples from aVirginia cave. They use carbon-14 dating todeft:- nine when prehistoric Indians lived in thevicinit!y.

Environmental Applications

In the field of environmental science,radioisotopes assist scientists in exploringthe world around us. Radioactive tracersfollow materials as they travel throughthe atmosphere, the waterways, and thefood chain and provide scientists withvital information about the delicatebalances in nature.

Phosphorus is a plant nutrient found instreams. The addition of a radioisotope ofphosphorus (phosphorus-32 or -33, forexample) into a stream permits scientiststo follow phosphorus up-take and observehow streams react to stressful changes

17k 12

resulting from high rainfall, heavy leaf

fall, and pollutants. Such studies are

referred to as phosphorus spiralling.

The radioisotope sulfur-35 permitsscientists to study the effects of coal run-

off and dry-acid deposition on plant life.

By injecting sulfur-35 into trees, for

instance, scientists are able to determine

how trees handle extra sulfur. Measuring

the ratio of radioactive sulfur-35 to stable

sulfur, scientists have found that some

trees send the extra sulfur to their roots,

and others seem to throw off the extra

sulfur into the atmosphere.

Environmentalscientists use sulfur-35

and carbon-14 to determine

the effects of pollutants on plant life.

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A naturally occurring radioisotope inthe Earth's upper atmosphere,beryllium-7, has important applicationsfor environmental studies. Because it iscarried to the ground in rainfall,beryllium-7 can be used to help determinethe age of sediments in lakes. This processpermits environmentalists to determine thesettling patterns for a variety of pollutantsentering the waterways, thus reducing thenumber of time-consuming chemicalanalyses necessary to characterize asediment.

Scientists at the National Bureau ofStandards are using radiocarbon dating todetermine the origin of some organicatmospheric contaminants such asmethane. By determining thecarbon-14-to-carbon-12 ratio, scientistscan determine whether a contaminantcomes from a living carbon source or afossil fuel such as gasoline.

Crime Stoppers

Radioisotopes assist investigators with avariety of chemical identificationproblems in a technique called activationanalysis. The technique is highly sensitiveand can be applied to almost everyelement on Earth. It is especially useful inidentifying trace quantities of materials.Criminal investigations frequently rely onactivation analysis to obtain physicalevidence for legal purposes. Items such aspaint, glass, tape, gunpowder, lead, andpoisons can be identified and oftenconnected to crimes. Using this technique,criminologists are able to gatherimportant evidence linking a suspect witha specific crime.

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Measurements of natural radioisotopes in thispainting proved it to be a forgery.

Activation analysis can also help proveor disprove the authenticity of oldpaintings by showing whether or notmodern materials are present. This andother techniques that rely on radioisotopesare routinely used by museums to spotforgeries and authenticate various worksof art.

'41

Activation analysis revealed that Winslc v Homer's firstversion of "Breezing Up" contained ships in differentlocations before they were moved over to balance thecomposition. (Courtesy of National Gallery of Art)

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RADIOISOTOPES IN INDUSTRY

With radioisotopes, manufacturers detecthidden flaws in hardware and make weartests on finished materials. Radioisotopes areessential to such remote applications asproviding lights for airplane runways in arcticregions and generating electrical energy for abroad range of missions in space. More andmore, radioisotopes have become a bridgebetween the laboratory and industry toimprove product quality.

Manufacturing Applications

The application of radioisotopes in manu-facturing depends, for the most part, on thefact that radiation loses energy as it passesthrough substances. Radioisotopes are used tomonitor and control thicknesses in themanufacture of plastics, paper, and photo-graphic film. The radiation that passesthrough the material is measured andcompared with the radiation that would passthrough a material of the proper thickness. Ifmore radiation is measured, the material istoo thin; if less is measured, the material istoo thick. Instruments sensitive to themeasurements activate controls to maintainthe proper thickness. In this way materialscan be monitored without being touched.

A portable radiography unit enables an inspector tocheck for cracks in aged metal pipes.

Radioisotopes also function in gaugingdevices, controlling everything from theamount of glue on a postage stamp to theamount of sugar in consumer foods.

Another industrial process, calledradiography, relies on radioisotopes toinspect many types of metals and machinesfor defects. The process is similar tomaterial inspection with x rays except thatthe radiation source is portable and theradiation more penetrating. The portablesource relies on a radioisotope that has avery penetrating radiation, such ascobalt-60. The portable source is easier touse, suitable for inspecting a wide range ofmaterials, and less expensive than a largemachine that would be necessary toproduce similar penetrating radiation.Radiography makes it possible to findinvisible cracks and manufacturing flaws instructural materials, welds, and cast metals.

Test-and-Wear Applications

Radioisotopes are used in industry andmanufacturing to develop strong anduniform products. For testing, radioisotopescan be added to such products as metalmachine parts, tire rubber, and engine oil.Using sensitive radiation detectors,researchers can quickly determine thelocation and amount of wear that thesematerials receive. Industry can thenmanufacture machines and materials thatlast longer and operate more reliably.

Radiotracers can be added to varioussolutions that are to be mixed together inmanufacturing to permit a readydetermination of mixing uniformity.Then, a simple radioactivity test allowsthe manufacturer to determine whenuniformity is reached in the mixing step.

17 42

By performing such tests while setting upmixing procedures, manufacturers can beassured of consistant product quality.

Consumer Product Applications

Radioisotopes have a number ofapplications for consumer goods. They areused to produce the "shrink wrap" filmused widely in packaging. First, specialfilm is treated with radiation. Later on,during packaging, the plastic film isheated, which causes it to shrink to fit theshape of the product. Similar processesare used on everything from soft drinkbottles to plastic insulation on wires.

Radioisotopes enable antistatic devicesin copy machines to keep paper sheetsfrom sticking and lint brushes to eliminatestatic electricity from clothing. A veryimportant application of radioisotopes inthe home is the small amount ofamericium -241 found in many householdsmoke detectors. The radioisotope is partof the sensing unit that triggers the alarmwhen smoke is present.

Ionizationchamber

Americium241source

IONIZATIONCHAMBER DETAIL

Electriccurrentsensingcircuit

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Entering smokeImpedes the flow ----1-of electric currentthrough Ionizedalr.

Flow ofelectric currentthroughionized air

Most household smoke detectors use small amountsof americium-241 to trigger an alarm when smokeis present.

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Radio luminescence, the light producedusing energy released during theradioactive decay process, is an importantcommercial application of radioisotopes.Luminous watch dials that depended onthe natural radioactivity of radium-226were commonplace years ago. IlluminatedExit signs that are powered by tritiumserve as reliable safety markers onpassenger aircraft, aboard ships, and inmany buildings. Emergency lighting onoffshore oil rigs and in lifeboats hasextended this use of tritium. Since 1984,tritium lights have been used to mark theedges of airport runways at remotecommunities in Alaska where conventionalelectric lighting systems are impractical.

Electricity in Small Packages

The heat generated by radioisotopespermits radioisotope-generators to be built toprovide electric power for remoteapplications. In early space missions withflight paths close to the Earth, electricalenergy was obtained from lightweightbatteries, fuel cells, and solar cells. Asmissions became more complex and distancesincreased, the need arose for more compactand longer-lived electrical generators.Electrical generators powered byradioisotopes such as plutonium-238 andstrontium-90 fulfill this need.

Radioisotope-powered generators arecurrently providing electrical energy for abroad range of space missions. Thesegenerators have powered our navigationaland weather satellites and have been essentialin space communications. They allow us toconduct experiments on the Moon and otherplanets. For the past 20 years, thesegenerators have been providing safe, reliable,

19 4

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Voyager 2, which passed Uranus on January 24,1986, draws its power from a radioactive heatsource.

and predictable performance in support ofour space program efforts. Many of ourNation's outer planetary missions couldnot have been accomplished without thereliable power provided by thesegenerators.

Here on Earth, generators powered byradioisotopes provide electricity whenordinary electrical sources are not

25 20

available. Such generators power weatherstations at both the North and SouthPoles, operate seismic sensing stations inremote locations, and power devicesplaced on the ocean floor for scientificinvestigations and national defense.

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A U.S. Air Force serviceman installs a tritium lighton an Alaskan airstrip.

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RADIOISOTOPES AND AGRICULTURE

Radioisotopes have played a role in manyimprovements in agriculture and hold greatpromise for the future, Insect infestationshave been controlled or eradicated wichradioisotopes. Radioisotope tracers in plantnutrients have increased our knowledge offertilizer utilization, achieving a moreeconomical application of fertilizers.Preservation of food by irradiation is thesubject of studies by the U.S. Department ofEnergy and the U.S. Department ofAgriculture. The International AtomicEnergy Agency, under charter by the UnitedNations, also has a number of coordinatedprograms to preserve foods of interest todeveloping countries. In a world thatInv: ices more than enough food for itsinhabitants but where millions still starve,the preservation of food by irradiation maywell be the key to a more efficientdistribution of food.

Insect Control Applications

Radioisotopes have been used successfullyto control insects that destroy crops. Thetechnique offers an alternative to chemicalpesticides. In the procedure, tl-ousands ofmale insect pests are raised in a laboratoryand exposed to sterilizing doses of radiationby being placed near a powerful radioisotopesuch as cobalt-60. This renders the maleinsects infertile. The sterilized males are thenreleased in an area where insect infestation isa problem. When these insects mate with thefemales in that area, the eggs produced bythe female will not be fertilized and,therefore, will not hatch. Pest populationsare then (1.-astically reduced and in soniccases completely eliminated.

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Screw worm infestation in the SoutheasternUnited States was eliminated by this tech-nique in the middle 1950s. Sterilizing maleinsects essentially solved the Mediterraneanfruit fly infestation in California in themiddle seventies. The successful control ofmosquitos and flies, such as the tsetse, melon,and horn, has also been demonstrated invarious countries throughout the world.Because chemical pesticides are not used, noharmful residues are left on crops, and theapproach does not kill beneficial insects.

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Farmers in the Southeast successfully eliminated thedestructive screw worm without pesticides by usingradioisotopes to sterilize the insect pests.

Plant Applications

The addition of radioisotope tracers tochemicals in fertilizers enables scientists tostudy the nutritional needs of plants.Badiotracers allow us to determine the up-take of chemicals by the plants and theefficiency of fertilization. This knowledgehelps the agronomists to raise a better anda greater variety of plants and to make

2823

more economic use of fertilizers, water,and land resources. Through such means, ithas been estimated that the worldwideconsumption of fertilizers could be cutin half.

In nature, some plant seeds grow intoplants with traits that differ from theparent plant. Some of these newvariations improve the plants, and othersdo not. Historically, people have selectedplants with useful traits and cultivated theseeds. Desirable properties includingincreased yields, improved resistance todisease, better adaptability, and earlierripening have sometimes been achieved byexposing seeds to radioisotopes. Withradioisotopes, researchers are often able toachieve the desired traits faster than ispossfule using chemical agents orconventional methods of crossbreeding.

One example of an important plant-change induced by radiation is thepeppermint plant. The Mitcham varietywas the only source of peppermint oil inthe United States. When it fell victim to awilt disease, soil fumigation andcrossbreeding techniques yielded plantseither still susceptible to the disease orplants with oils that had unsatisfactoryflavors. Radiation techniques led to adisease-resistant variety of the plant withproperly flavored peppermint oil.

Food Irradiation Applications

One of the most exciting applications ofradiation from radioisotopes is thepreservation of foods for eAtended periodsof time. Irradiation makes chemicaladditives and refrigeration unnecessary.

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4

The technique also requires less energythan other food preservation methods.Preserving food by irradiation is understudy by the U.S. Department ofAgriculture; however, it has been slow todevelop in the United States, probablybecause of the extensive availability ofrefrigeration and lack of economicincentive and public support. However,the technique is having a great impactabroad, particularly in developingcountries where many people do not haveenough food to eat, in part, because offood spoilage. The usefulness of foodpreservation by radiation is bestillustrated by our manned spaceexplorations. Astronauts took foodsterilized by irradiation to the moon andon shuttle flights. Moreover, theypreferred it over all other types ofpreserved food.

Food is irradiated by exposing it togamma rays from radioisotopes. Cobalt-60is the radioisotope in general use, but theFederal government has recentlyauthorized the building of a commercial-type, food-irradiation facility usingcesium-137. The radiation process destroysbacteria, viruses, molds, and insects thatcause spoilage and disease.

Exposing food to radiation does notmake it become radioactive, and itsnutritional value is not significantlychanged. Irradiating food increases itsshelf life, kills insects in grains andstored foods, inhibits the sprouting ofvegetables such as potatoes and onions,delays the ripening of certain fruits,and, at the highest doses, completelysterilizes food.

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FOODS APPROVED BY FDA FOR. IRRADIATION TREATMENT

Food Plif 00SC' Date Approved

Fruits and To slow growth andvegetables ripening and to

control insects

April 1986

Pork To controlTrichinella spiral's(the parasite thatcauses trichinosis)

July 1985

Wheat, wheat To control insects Aug. 1963flour

The U.S. Food and DrugAdministration (FDA) has establishedregulations that approved the gammaradiation of various herbs, spices, naturalflavorings, and vegetable seasonings. In1985, the FDA approved the commercialirradiation of pork to destroy the parasitecausing trichinosis. The FDA hasproposed standards covering foodirradiation practices and irradiated foodlabeling requirements. Labels willidentify such foods and conditionsof treatment.

Gamma irradiation of food will notrender it unsafe for consumption. A 1984International Atomic Energy Agency

26

bulletin states that more than 25 years oftesting the wholesomeness of radiation-preserved food throughout the worldshowed no harmful effects from itsconsumption. In 1983, the government ofJapan sponsored the Asian, RegionalCooperative Project on Food Irradiation.Eleven countries participated in theprogram: Bangladesh, India, Indonesia,Japan, Republic of Korea, Malaysia,Pakistan, Philippines, Sri Lanka,Thailand, and Vietnam. Despite the lackof evidence of any ill affects, the FDA iscontinuing studies to ensure that'allirradiated food is safe to eat.

This symbol is used internationally to indicatefoods that are preserved using radiation. Thetechnique, approved for some foods in the UnitedStates, does not reduce the nutritional quality ofthe food.

TODAY AND TOMORROW...

When natural radioactivity wasdiscovered just before the turn of thecentury, scientists could scarcely haverealized the benefits that would bederived from the application of radiationfrom radioisotopes. Radioisotopes havebeen present since the beginning of time,but their practical applications are justbeginning to emerge. Radioisotopes haveimproved our methods of diagnosing andtreating diseases and powered ourexplorations of space. With radioisotopes,we can chart the course of eventsoccurring before historical records werekept. With radioisotopes, we can improveour environment, make better industrialproducts, grow bigger and better plantsmore economically, and preserve foods ina new way. Scientists now realize thatthese are only the preview of things tocome and that the future holds thepromise of many new and innovativeways in which radioisotopes can improveour lives.

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!-.

DOE produces publications to fulfill a statutorymandate to disseminate information to thepublic on all energy sources and energyconservation technologies. These materials arefor public use and do not purport to present anexhaustive treatment of the subject matter.

This is one in a series of publications on nuclearenergy. For additional information on a specificsubject, please write to ENERGY,P.O. BOX 62, OAK RIDGE, TN 37830.

U.S. Department of Energy

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