O

OO

U.S. Nuclear Regulatory

Commission

THE REGULATION

AND USE OF

RADIOISOTOPES IN

TODAY'S WORLD

The regulation and use of radioisotopes in today’s world

1

More than 100 years ago, scientists Introduction

discovered that many elements commonly found on earth occur in different atomic configurations. These varying configurations, called isotopes,

were found to have identical electronically charged particles and identical

chemical properties, but different

atomic weights and physical properties.

It was soon discovered that some isotopes of elements were radioactive.

The dense central portion (called the

nucleus) of an atom of the element

emits energy in several different forms.

Radioisotopes are simply atoms with

nuclei that are seeking a more stable

nuclear configuration by emitting radiation. Scientists have learned that

more radioisotopes could be created by

subjecting certain elements to radiation

inside a nuclear reactor or bombarding them using a particle accelerator.

Gradually we have learned to harness

these radioisotopes for use in our modern, high-tech world. In this brochure

are described some of the most common uses for radioisotopes, as well as

the relative benefits and hazards involved in their applications. The appendix at the end of this brochure describes various uses of radioisotopes

in this country.
The regulation and use of radioisotopes in today’s world

2

INSIDE THE ATOM Protons...are the nucleus

which consists of

protons, which carry

positive electric

charges...

Neutrons Electrons ...and neutrons,

which carry no

electric charge.

Encircling the

nucleus are electrons

which carry negative

electric charges.

Also explained are the

properties of radiation

that enable it to change

the physical characteristics of certain materials. Because they emit

tell-tale ionizing radiation, extremely small

quantities of radioisotopes can be traced

and measured using special equipment.

This property makes them a useful

diagnostic tool in medicine. The

radiation from some radioisotopes can

penetrate thick metal parts and provide

a way to “see” inside objects that are

impenetrable to light. Radiation

deposits sufficient energy in human

tissue to disrupt normal cell function as

it passes through, thus providing

a unique method of attacking and

destroying cancerous cells and tumors.

Radiation can also be used to kill bacteria and germs that contaminate medical instruments and some foodstuffs.

Finally, this brochure describes the responsibilities of the U.S. Nuclear

Regulatory Commission (NRC), some

other Federal agencies, and the States,

in regulating the manufacture, use, and

possession of radioactive materials.
The regulation and use of radioisotopes in today’s world

3

Alpha

Beta

Medical x-ray

Gamma

Neutron

Paper Wood Concrete

A few radioisotopes occur naturally but

most are man made. A radioisotope is

typically described by its name followed by a number, such as carbon-14

(C-14) or fluorine-18 (F-18). The

number represents the atomic weight

or the total number of protons and neutrons that make up the atom’s nucleus.

Radioisotopes have unique properties

that make them useful tools in solving

problems.

Three predominant types of radiation

are emitted by radioisotopes: (1) alpha

particles, (2) beta particles, and

(3) gamma rays. The different types

of radiation can penetrate materials of

varying thicknesses such as paper,

body tissue, or concrete. A single sheet

of paper will stop an alpha particle,

which, because

it is heavy, has

very little penetrating power.

Alpha emitters

are typically

used in smoke

detectors. A thin

sheet of metal

will stop a beta

particle, which,

1. Radioisotopes emit

different kinds of

radiation.

Why Are

Radioisotopes

Useful?

Penetrating power

of radiation
The regulation and use of radioisotopes in today’s world

4

2. The length of a

radioisotope’s life

is predictable.

because it is lighter, is more penetrating than an alpha particle. Beta emitters such as strontium-90 (Sr-90) are

used in the treatment of eye disease.

Gamma rays, which have no charge

or weight, can be extremely energetic

and highly penetrating. Several meters

of concrete or several millimeters of

other dense materials, such as lead, are

needed to block gamma rays. Radioisotopes that emit gamma rays are used

frequently in medical applications

against tumors, and in industry to check

for cracks or flaws in valves and piping. Because of their varying penetrating properties, radioisotopes can be

manipulated to perform different tasks.

The process of radioactive decay, in

which radioisotopes lose their radioactivity over time, is measured in halflives. A half-life of a radioactive material is the time it takes one-half of

the atoms of the radioisotope to decay

by emitting radiation. The half-life of

a radioisotope can range from fractions

of a second (radon-220) to millions of

years (thorium-232). When radioisotopes are used in industry or medicine, it is vital to know how rapidly

they disappear, so that the precise

amount of radioisotope available for

the medical procedure or industrial use

is known.
The regulation and use of radioisotopes in today’s world

5

3. Radioisotopes of a

chemical element

behave in the same

manner as a stable,

nonradioactive

element.

We can trace the movement of a chemical element by using a radioisotope of

that element. For instance, the chemical element iodine concentrates naturally in the thyroid. By using a radioactive isotope of iodine as a tracer, a

picture can be taken of the material’s

path through the body and its deposit

in a specific organ.

One Half-Life

Four Half-Lives

Six Half-Lives

Ten Half-Lives

After one half-life only half the

radioactivity remains.

After ten half-lives only one thousandth

of the radioactivity remains.

Half-life decay
The regulation and use of radioisotopes in today’s world

6

Radioisotopes come from three

sources: (1) from nature, such as

radon in the air or radium in the soil;

(2) from machine-produced nuclear

interactions in devices, such as linear

accelerators and cyclotrons; or

(3) from nuclear reactors.

A linear accelerator is a long, straight

tube in which charged particles gain

energy through oscillating electromagnetic fields. A cyclotron is an accelerator in which charged particles travel in

an almost circular path, rather than in a

straight path as in a linear accelerator.

Radioisotopes produced in linear accelerators are used in some modern

nuclear medicine procedures.

The nuclear reactors that produce

radioisotopes bombard atoms with

high-energy neutrons. The research reactors used for this purpose do not produce electricity and are much smaller

in size and power than large power reactors. Reasearch reactors are mostly

used for training and for identifying the

composition of certain elements.

Forty-seven research reactors are

licensed by the NRC to operate in the

United States. They are located mostly

at large universities.

Because of the potentially hazardous

properties of radioisotopes, their use

must be closely regulated to ensure that

public health and safety are protected.

Where Do

Radioisotopes

Come From and Who

Regulates Their Use?
The regulation and use of radioisotopes in today’s world

7

What Is the Role

of the Nuclear

Regulatory

Commission?

The licensing and regulation of radioisotopes in the United States are shared

by the NRC, the U.S. Environmental

Protection Agency (EPA), and many

State governments. The EPA is also

responsible for, among other things,

setting air emission and drinking

water standards for radionuclides. The

States regulate radioactive substances

that occur naturally or are produced by

machines, such as linear accelerators or

cyclotrons. The Food and Drug Administration (FDA) regulates the manufacture and use of linear accelerators; the

States regulate their operation.

The NRC is the Federal agency given

the task of protecting public health and

safety and the environment with regard

to the safe use of nuclear materials.

Among its many responsibilities, the

NRC regulates medical, academic, and

industrial uses of nuclear materials generated by or from a nuclear reactor.

Through a comprehensive inspection

and enforcement program, the

NRC ensures that these facilities

operate in compliance with strict

safety standards.

The NRC has relinquished its

authority to regulate certain

radioactive materials, including

some radioisotopes, to most of

the States. These States, which

have entered into an agreement assuming this regulatory authority from
The regulation and use of radioisotopes in today’s world

8

the NRC, are called Agreement

States, and are shown on the map below. Agreement States, like the NRC,

regulate reactor-produced radioisotopes within their borders and must

provide at least as much health and

safety protection as the NRC.

The NRC maintains approximately

6,000 licenses for the use of radioactive materials, and the Agreement

States maintain approximately 16,000

Map of Agreement States

Agreement State

MA

CT RI

VTNH ME

NY

PA NJ

OH

MD

DE

VA

W

MI

IN

KY

NC

TN

IL

SC

AL GA

FL

MS

MO

A

TX

OK

KS

LA

IA NE

WI

MN

ND

SD

WY

MT

CO

NM AZ

CA

NV

UT

ID

OR

WA

Source: Nuclear Regulatory Commission
The regulation and use of radioisotopes in today’s world

9

materials licenses. Every license specifies the type, quantity, and location

of radioactive material that may be

possessed and used. When radioactive

material is transported, special packaging and labeling are required. Also

specified in each license are the training and qualification of workers using

the materials, specific procedures for

using the materials, and any special

safety precautions required. Every licensee is inspected periodically either

by the NRC or the Agreement State to

ensure that radioactive materials are

being used and transported safely. Violators of regulatory requirements are

subject to fines and other enforcement

actions, including loss of license.
The regulation and use of radioisotopes in today’s world

10

About one-third of all patients admitted to U.S. hospitals are diagnosed or

treated using radioisotopes. Most major hospitals have specific departments

dedicated to radiation medicine. In all,

about 112 million nuclear medicine or

radiation therapy procedures are performed annually, with the vast majority used in diagnoses. Radioactive materials used as a diagnostic tool can

identify the status of a disease and minimize the need for surgery, reducing the

risks from postoperative infection.

Radioisotopes give doctors the ability

to “look” inside the body and observe

soft tissues and organs, in a manner

similar to the way x-rays provide images of bones. Radioisotopes carried

in the blood also allow doctors to detect clogged arteries or check the functioning of the circulatory system.

Some chemical compounds concentrate naturally in specific organs or tissues in the body. For example, iodine

collects in the thyroid while various

compounds of technetium-99m*

(Tc-99m) collect in the bones, heart,

and other organs. Taking advantage

of this proclivity, doctors can use

radioisotopes of these elements as

tracers. A radioactive tracer is chemically attached to a compound that will

Diagnostic

Applications

*

The “m” refers to “metastate,” which pertains

to the isotope’s short half-life and elevated

energy state.

How Are

Radioisotopes

Used in Medicine?
The regulation and use of radioisotopes in today’s world

11

Gamma camera used to

detect dysfunctional activity

in body organs

concentrate naturally in an organ or tissue so that a picture

can be taken. The process of

attaching a radioisotope to a

chemical compound is called

labeling.

To detect problems within

a body organ, doctors use

radiopharmaceuticals or

radioactive drugs. Radioisotopes that have short halflives are preferred for use in

these drugs to minimize the radiation dose to the patient. In

most cases, these short-lived

radioisotopes decay to stable

elements within minutes, hours, or days,

allowing patients to be released from the

hospital in a relatively short time.

The radioisotope used in about 80 percent of nuclear diagnostic procedures

is Tc-99m. The penetrating properties of its gamma rays and its short

(6-hour) half-life help reduce risk to

the patient from more prolonged radiation exposure.

Because of their short half-lives, certain radiopharmaceuticals must be produced, shipped to the hospital, and then

used within a couple of weeks. Shortlived radionuclides such as Tc-99m,

gallium-67, and thallium-201 are often used to diagnose the functioning of
The regulation and use of radioisotopes in today’s world

12

Tracer used in the body of a

65-year old man indicating

bone density problems as a

result of a thyroid condition

Photo: Courtesy of Appleton

& Lange, from “A Clinical

Manual of Nuclear Medicine,” by John Walker and

Donald Margouless, 1984.

the heart, brain, lung, kidney, or liver.

For example, Tc-99m is used to diagnose osteoporosis, a condition caused

by calcium deficiency in older people,

especially women.

To evaluate the presence of heart disease, a radioisotope is injected into a

patient’s bloodstream while he or she

is exercising on a treadmill. The

radioisotope travels toward the heart,

allowing doctors to follow the blood

flow on a screen. While looking at the

image, doctors can check for reduced

blood flow through the arteries, a possible signal of heart disease.

Nuclear imaging is also used to evaluate brain function. Organic radiochemicals are labeled with F-18 and

then injected into the bloodstream. A

device called a gamma camera detects

radiation emitted from the organ, displaying an image that can enable the

physician to detect blockages or other

dysfunctional activity.

For some diagnostic tests, the patient

need not come into contact with radioactivity at all. The tests are performed

on blood or other fluids taken from the

patient, using a procedure called radioimmunoassay. These tests can detect

some diseases by identifying and measuring the amounts of hormones, vitamins, enzymes, or drugs in the body.
The regulation and use of radioisotopes in today’s world

13

The same property that makes radiation hazardous can also make it useful in helping the body heal. When

living tissue is exposed to high levels

of radiation, cells can be destroyed or

damaged so they can neither reproduce nor continue their normal functions. For this reason radioisotopes are

used in the treatment of cancer (which

amounts to uncontrolled cell division).

Although some healthy tissue surrounding a tumor may be damaged during the

treatment, mostly cancerous tissue can

be targeted for destruction.

A device called a teletherapy unit destroys malignant tumors with gamma

radiation from a radioisotope such as

cobalt-60 (Co-60). Teletherapy units

use a high-energy beam of gamma rays

to reduce or eradicate tumors deep

within the body. These units are licensed by the NRC because they use

byproduct material that is produced

only by a nuclear reactor.

Another treatment, called brachytherapy, destroys cells by placing the

radioisotope (in the form of a sealed

source) directly into the tumor. Generally, two techniques are used for this

type of treatment: (1) direct, manual

implantation of a radiation source by a

physician or (2) automated implantation using a device called a remote

afterloader. The NRC as well as

Therapeutic

Applications
The regulation and use of radioisotopes in today’s world

14

Agreement States license these brachytherapy devices. Using

these devices, a small,

thin wire or sealed

needle containing radioactive material, such as

iridium-192 (Ir-192) or

iodine-125 (I-125), is

inserted directly into the

cancerous tissue. The

radiation from the isotope attacks the tumor as long as the

device is in place. When the treatment

is complete, long-lived material (Ir-192)

is removed, but the short-lived radioisotopes (I-125) may be left permanently. This technique is used frequently to treat mouth, breast, lung, and

uterine cancer.

Brachytherapy and teletherapy procedures are performed only in hospitals

or clinics by trained medical personnel.

Strict controls and safety requirements

set by the NRC or the Agreement States

must be followed. For example, treatment rooms must have adequate

shielding to prevent scattered radiation

from penetrating into an adjacent room.

Radiation monitors must be used and

patients carefully observed at all times

during treatment.

Many types of cancer, such as

Hodgkin’s disease (cancer of the

Brachytherapy device

Photo: Courtesy of Nucletron

International B.V.
The regulation and use of radioisotopes in today’s world

15

lymph glands) and cancers of the cervix, larynx, and skin, can be treated by

radiation alone. Boron capture neutron

therapy has been used on a trial basis

recently to treat potentially fatal brain

cancer. In this procedure, the diseased

brain tissue incorporates a neutronabsorbing isotope and then is exposed

to neutron radiation originating from a

nuclear research reactor. The energy

and radiation emitted as a result of the

neutron activation slow down the

growth of cancer cells and, in some

cases, completely kill them.

The overall objectives of NRC’s safety

rules for radiation medicine are to ensure that patients receive only the exposure medically prescribed and that the

radiation is delivered in accordance with

the physician’s instructions.

NRC regulations require that physicians and physicists have special training and experience to practice

radiation medicine. The training emphasizes safe operation of nuclearrelated equipment and accurate

recordkeeping.

When using radiation as a medical

treatment, the physician weighs the potential benefits against the risk of side

effects. Intense radiation exposure often destroys tumors that would prove

fatal, but side effects such as hair loss,
The regulation and use of radioisotopes in today’s world

16

How Are

Radioisotopes

Used in Industry?

Well-logging device

Detector

Bore hole probe

Shield

reduced white blood cell count, and

nausea can be severe and must be monitored carefully.

Radioisotopes are used in many of

today’s industrial processes. Hightech methods that ensure the quality

of manufactured products often rely

on radiation generated by radioisotopes. To determine whether a well

drilled deep into the ground has the

potential for producing oil, geologists

use nuclear well-logging, a technique

that employs radiation from a radioisotope inside the well to detect

the presence of different materials.

Radioisotopes are also used to sterilize instruments; to find

flaws in critical steel parts

and welds that go into

automobiles and modern

buildings; to authenticate

valuable works of art;

and to solve crimes by

spotting trace elements

of poison, for example.

Radioisotopes can also

eliminate dust from film

and compact discs as

well as static electricity

(which may create a fire

hazard) from can labels.
The regulation and use of radioisotopes in today’s world

17

Radiation can destroy germs, bacteria,

and other harmful organisms that contaminate medical supplies, blood supplies, and even our food. Over the

years, we have learned how to safely

treat these items with radiation to sterilize or preserve them when other

methods such as boiling or using

chemical preservatives are either impractical or not as effective.

Medical supplies, such as rubber

gloves, cloth bandages, syringes,

and contact lens solution, can be

sterilized by using an irradiator.

An irradiator exposes the materials

to gamma radiation, usually from

Co-60.

Bacteria in foods can be destroyed by

using radiation. Astronauts, for example, take food into space that often

has been preserved using radiation.

Food irradiation is discussed in greater

detail later in this brochure.

The NRC regulates irradiators to protect workers and the public but, with

some exceptions, does not specify the

types of products that may be irradiated. The NRC does not evaluate the

quality of irradiated products or the

Irradiation and

Treatment of Materials

With Radioisotopes
The regulation and use of radioisotopes in today’s world

18

technical or economic feasibility of

product irradiation.

In the United States, food safety is

regulated by the FDA and the U.S. Department of Agriculture (USDA).

There is an important difference between exposing materials to radiation

An industrial irradiator used for food products consists of a room

with concrete walls 2 meters thick and a radiation source (Co-60).

A conveyor system automatically moves the products into the room

for irradiation and then removes them. When it is necessary for

personnel to enter the room, the source is lowered to the bottom of

the pool, where water absorbs the radiation energy and protects

the workers.

Conveyor

System

Unloading

Processed

Product

Loading

Control

Console

Irradiation

Room

Storage

Pool

Radiation Source

Radiation Shield

Diagram: Courtesy of

Food Technology Service, Inc.
The regulation and use of radioisotopes in today’s world

19

from an irradiator and exposing them

to radiation from a reactor. The

gamma radiation from Co-60 in an irradiator kills bacteria and germs, but

does not leave any radioactive residue

or cause any of the materials exposed

to become radioactive themselves.

This is because the Co-60 is contained

in stainless steel capsules and does not

commingle with the product being irradiated. This differs, however, from

the effects of neutron radiation. Material can become radioactive after exposure to neutrons from a reactor or

linear accelerator because the neutrons are absorbed by the nucleus of

the atoms in the material, which then

form different radioactive isotopes or

elements (also referred to as neutron

activation).

In manufacturing, radiation can

change the characteristics of materials, often giving them features that are

highly desirable. For example, wood

and plastic composites treated with

gamma radiation are used for some

flooring in high-traffic areas of department stores, airports, hotels, and

churches, because they resist abrasion

and ensure low maintenance. Some

gemstones, such as blue topaz, can be

given a more pleasing color using neutron radiation treatment.
The regulation and use of radioisotopes in today’s world

20

Measuring and

Testing Applications

Although there might be some

residual radiation from neutron

bombardment of gemstones and other

consumer products, the half-life

of these materials is generally so

short (seconds or hours) that risk

to the public is extremely low. To ensure that the products are manufactured correctly, manufacturers and

distributors of these materials must be

licensed by the NRC.

Today, luminous watch dials are

painted with tritium or promethium147 replacing radium used many years

ago. These radioisotopes trigger a

chemical reaction with other materials

upon contact, which then give off a

“glow.” These materials are sometimes

placed in gun sights or clocks and

watches so they can be used at night.

One frequently sees “exit” signs illuminated by tritium as safety markers on

passenger aircraft, aboard ships, and in

many buildings. Some gas lantern

mantles are manufactured with the

radioisotope thorium to provide a bright

light when burned.

As radiation from a radioisotope passes

through matter, it is scattered or absorbed. The amount of radiation passing completely through depends on the

thickness and density of the matter. This

property makes radiation useful for many

manufacturing quality control processes.

Gauge, luminous watch dial

and smoke detector
The regulation and use of radioisotopes in today’s world

21

For example, radioisotopes in gauges

are used to monitor and control the

thickness of sheet metal, textiles, aluminum foil, newspaper, copier paper,

plastics, and photographic film as they

are manufactured. Radiation penetrates

the material as it is processed, and

detectors measure the amount of radiation passing through and compare it to

the amount that should be detected for

the desired thickness of material. If the

readings are too high or too low, controls in the manufacturing process can

be activated to correct the problem.

This is accomplished with a high

degree of accuracy, and the materials need not

be touched by human hands.

Radioactive

tracers can also

be used in the

machine-tools

industry to measure wear on cutting tools and

drills. Gauges

also play a role

in the measurement of everyday objects, such

as the amount of

glue on a postage stamp, the

The use of portable gauges

is widespread in industries

such as agriculture and

construction. In the illustration on the left, the gamma

source is placed underneath

the surface of the ground

through a tube. Radiation is

then transmitted directly to

the detector on the bottom

of the gauge, allowing accurate measurements of

compaction.

On the right, the neutron source remains

above the surface, and

radiation is emitted into

the ground and scattered

back to the detector to

provide a measurement

of the moisture content.

Gauge

Detectors

Radiation

Source

Surface

Depth

Direct transmission

Radiation

Gauge

Detectors

Source

Surface

Backscatter
The regulation and use of radioisotopes in today’s world

22

level of liquid in

canned beverages,

the amount of air

whipped into ice

cream, and the

amount of tobacco

packed into a cigarette. Other gauge

and nuclear instrument applications

include: (1) monitoring the structural

integrity of roads, buildings, and

bridges; (2) exploring for oil, gas, and

minerals; and (3) detecting explosives

in luggage at airports. To ensure adequate water supplies, radioisotopes

are used to measure water runoffs

from rain and snow, flow rates of

streams and rivers, and leakage from

lakes, reservoirs, and canals.

Radioisotopes can also be used to

test for the presence of certain materials. For example, a small amount of

americium-241 is found in most

smoke detectors used in homes and

offices. This radioisotope is part of

the sensing unit that triggers an alarm

when smoke is present.

Portable gauge used to test

the structural integrity of

roads and bridges
The regulation and use of radioisotopes in today’s world

23

Portable radiography

camera used to test for

cracks in metal

A process called industrial radiogra- Industrial Radiography

phy is used to inspect many metal

parts and welds for defects. A sealed

radiation source, usually Ir-192

or Co-60, beams radiation at the object to be checked. Special photographic, or radiographic, film on the

opposite side of the source is exposed

when it is struck by radiation passing

through — like an x-ray. More radiation will pass through if there are

cracks, breaks, or other flaws in the

metal parts and will be recorded on the

film. Therefore, structural problems

can be detected by studying the film.

Radiography is used throughout

industry. For example, jet engine

turbine blades are radiographed to ensure that

internal cooling passages are manufactured

properly.

The NRC or Agreement

States license radiographers and periodically inspect them to

ensure they follow safety

procedures.
The regulation and use of radioisotopes in today’s world

24

Radioisotopes have played an important role in improving agricultural science. Radioisotopes are used as a research tool to develop new strains of

food crops that are

more resistant to disease, are of higher

quality, allow earlier

ripening, and produce

a higher yield. When

insects are sterilized

with radiation, they

mate without producing offspring, thus

providing some control of insect population growth. With

fewer pests, food crops can flourish.

This technique has eliminated screw

worm infestation in the southeastern

United States and Mexico and has

helped control the Mediterranean fruit

fly in California. It has also been used

to control mosquitoes and flies throughout the world.

Radioisotope tracers in plant nutrients

enable scientists to make discoveries

that have increased the effectiveness

of fertilizer.

A major factor in successful crop production is the presence of an adequate

water supply. Nuclear moisture density gauges can monitor the moisture

How Are

Radioisotopes Used

in Agriculture?
The regulation and use of radioisotopes in today’s world

25

content of soil, helping make the most

efficient use of limited water sources.

The NRC and the Agreement States license byproduct radioactive materials used in these agricultural applications in the United States.

Radiation can be used to destroy bacteria in food and control insect and

parasite infestation. Since 1963, the

FDA has approved irradiation as a

method to inhibit sprouting and to delay ripening in many fresh fruits and

vegetables. The FDA has more recently approved the use of irradiation

to control insects in food, trichina in

pork, and bacteria in poultry, spices,

and seasonings.

Currently, irradiation is used in the

United States on very few food

items; however, some spices are irradiated. In 1992, the USDA also

approved the commercial irradiation of

poultry, and in 1999,

approved commercial

irradiation of meat.

The FDA has established regulations

controlling irradiation

of food. Irradiated

food must clearly

Food Irradiation and

Its Safety
The regulation and use of radioisotopes in today’s world

26

display the radura logo (a green,

flower-like, international symbol for

irradiation) and words such as

“treated with radiation.”

Governments in about 37 countries have approved irradiation of

some 40 foods. In this country

only one commercial facility is

devoted solely to irradiating food

products. It is located in Florida

and licensed by the State. That facility irradiates strawberries and citrus

fruits by exposing them to gamma rays

from a radioactive source. When not

in use, the radiation sources are safely

stored in a pool of water.

Although it is a relatively new commercial process, food irradiation has been

studied at length for over 40 years.

According to the FDA, research to date

has turned up no evidence of adverse

health effects from irradiation of the

treated food. The radiation passes

through the food leaving no radioactive

residue. Some concerns have been

raised regarding the chemical changes

that may alter the finished food product. However, research has shown that

changes in flavor and texture caused by

irradiating food are similar to changes

due to canning or freezing. Studies are

continuing to ensure that all irradiated

food is safe to eat.

Radura logo
The regulation and use of radioisotopes in today’s world

27

Through a method called radiocarbon

dating, archaeologists can determine

when formerly living materials were

last alive. This procedure relies on the

presence of C-14, a naturally occurring,

long-lived radioisotope present in all

living things.

The ratio of C-14 to C-12 in the atmosphere has been relatively constant

throughout history. When an animal

or plant dies, it stops taking in carbon,

and the amount of C-14 in its tissue

begins to decrease through the process

of radioactive decay. Comparing the

C-14 to C-12 ratio in dead material

with the “living ratio” enables us to calculate how long ago the plant or animal lived. This method was used to

determine the approximate age of two

major archaeological discoveries in recent decades: the Shroud of Turin and

the Dead Sea Scrolls. C-14 analysis

has also been used during space missions to test for life on Mars.

Heat generated by radioisotopes is

used to power small generators used

for remote applications, such as in

space exploration.

Radioisotope-powered electrical generators have been used to power exploration space craft, navigational and

weather satellites, and communication

Geology, Archeology,

and Space

What Are Other Uses

of Radioisotopes?
The regulation and use of radioisotopes in today’s world

28

satellites. They allow

us to operate weather

stations at the North

and South Poles, seismic sensing stations

in remote locations, and devices

placed on the

ocean floor for

scientific investigations and national defense.

The Department

of Energy (DOE)

manufactures

radioactive thermal generators,

which are powered

by plutonium-238

and Sr-90. The

NRC has provided

technical assistance for some of these

applications.

A procedure called activation analysis is frequently used

to identify trace quantities of materials such as glass, tape, gunpowder,

lead, and poisons that are important to

criminal investigations. Samples of

SiliconGermanium

Thermocouples

Cold Side

Plutonium-238 Fuel

Hot Side

Cooling

Tubes

Cooling

Fins

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

ow does a radioisotope thermoelectric

generator (RTG) produce electricity?

The “fuel”—a plutonium isotope that

can't explode—“decays,” or loses its

radioactivity, giving off heat. That

heat is absorbed by a device called a

thermocouple, which consists of

a compound of two metals—silicon

and germanium—that are “doped.”

“Doping” the metals—adding

impurities to them—changes their

electrical 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 a

voltage. Gas circulating

through cooling tubes

keeps the RTG from

getting too hot, and fins

dissipate the heat.

The thermocouple was first

demonstrated early in the last

century, but the efficiency was too

low to be practical. In the 1950s,

researchers discovered they could

get higher efficiencies from a thermocouple by using “semiconductor” materials such as silicon and

germanium. After that, there was

no looking back. Today’s conversion efficiency is about 5 percent,

but with some of the conversion

technologies now under development, tomorrow’s efficiencies are

expected to be at least 20 percent.

Diagram: Courtesy of the

Nuclear Energy Institute
The regulation and use of radioisotopes in today’s world

29

materials are placed in a nuclear reactor and bombarded with neutrons. The

induced radiation produces a “fingerprint” of the elements in the sample.

In addition, activation analysis can prove

the authenticity of old paintings by detecting whether certain modern materials are present. Museums routinely use

this and other techniques that rely on

radioisotopes to spot forgeries.

Radioisotopes are used to detect pollution in the air, water, and soil.

Sources of acid rain and greenhouse

gases that may be causing global

warming can be traced using radioisotopes. In addition, electron beam

radiation can be used to remove gaseous pollutants such as sulphur dioxide or nitrogen oxide, both harmful

gases emitted from coal-fired power

plants and other industries.

When used properly, radioisotopes are

a productive part of today’s world. The

NRC and the Agreement States remain

committed to protecting public health

and safety in the use of these nuclear

materials by inspecting medical, academic, and industrial applications carefully, and monitoring users to ensure

safe practices.

Conclusion
The regulation and use of radioisotopes in today’s world

30

Cesium-137

Used to treat cancerous tumors...to

measure correct patient dosages of

radioactive pharmaceuticals...to

measure and control the liquid flow

in oil pipelines...to tell researchers

whether oil wells are plugged by

sand...and to ensure the right fill level

for packages of food, drugs and other

products. (The products in these packages do not become radioactive.)

Chromium-51

Used in research in red blood cell survival studies

Cobalt-57

Used as a tracer to diagnose pernicious anemia

Cobalt-60

Used to sterilize surgical instruments...and to improve the safety

and reliability of industrial fuel oil burners. Used in cancer treatment, food irradiation, gauges, and radiography.

Copper-67

When injected with monoclonal

antibodies into a cancer patient, helps

the antibodies bind to and destroy the

tumor.

Americum-241

Used in many smoke detectors for

homes and businesses...to measure

levels of toxic lead in dried paint

samples...to ensure uniform thickness

in rolling processes like steel and paper production...and to help determine

where oil wells should be drilled.

Cadmium-109

Used to analyze metal alloys for

checking stock, scrap sorting.

Calcium-47

Important aid to biomedical researchers studying the cellular functions and

bone formation in mammals

Californium-252

Used to inspect airline luggage for hidden expolsives...to gauge the moisture

content of soil in the road construction

and building industries...and to measure the moisture of materials stored

in soils.

Carbon-14

Major research tool. Helps in research

to ensure that potential new drugs are

metabolized without forming harmful

by-products. Used in biological research, agriculture, pollution control,

and archeology.

Appendix: Some of the Major Uses of

Radioisotopes in the United States.
The regulation and use of radioisotopes in today’s world

31

Iridium-192

Used to test the integrity of pipeline

welds, boilers and aircraft parts and

in brachytherapy/tumor irradiation.

Iron-55

Used to analyze electroplating solutions and to detect the presence of

sulphur in the air. Used in metabolism

research.

Krypton-85

Used in indicator lights in appliances

such as clothes washers and dryers,

stereos, and coffeemakers...to gauge

the thickness of thin plastics and sheet

metal, rubber, textiles and paper... and

to measure dust and pollutant levels.

Nickel-63

Used to detect explosives, and in voltage regulators and current surge protectors in electronic devices, and in

electron capture detectors for gas

chromatographs.

Phosphorus-32

Used in molecular biology and genetics research.

Curium-244

Used in mining to analyze material

excavated from pits...and slurries

from drilling operations.

Gallium-67

Used in medical diagnosis

Iodine-123

Widely used to diagnose thyroid disorders and other metabolic disorders

including brain function.

Iodine-125

Major diagnostic tool used in clinical

tests and to diagnose thyroid disorders. Also used in biomedical research.

Iodine-129

Used to check some radioactivity

counters in in vitro diagnostic testing

laboratories.

Iodine-131

Used to treat thyroid disorders.

(Former President George Bush and

Mrs. Bush were both successfully

treated for Graves’ disease, a thyroid

disease, with iodine-131.)
The regulation and use of radioisotopes in today’s world

32

Phosphorus-33

Used in molecular biology and genetics research.

Plutonium-238

Has powered more than 20 NASA

spacecraft since 1972.

Polonium-210

Reduces the static charge in production of photographic film and other

materials

Promethium-147

Used in electric blanket thermostats...and to gauge the thickness of

thin plastics, thin sheet metal, rubber,

textile and paper.

Radium-226

Makes lighting rods more effective.

Selenium-75

Used in protein studies in life science

research.

Sodium-24

Used to locate leaks in industrial pipe

lines...and in oil well studies.

Strontium-85

Used to study bone formation and

metabolism.

Strontium-90

Used in survey meters by schools, the

military and emergency management

authorities. Also used in cigarette

manufacturing sensors and medical

treatment.

Sulphur-35

Used in genetics and molecular biology research.

Technetium-99m

The most widely used radioactive

pharmaceutical for diagnostic studies

in nuclear medicine. Different chemical forms are used for brain, bone,

liver, spleen and kidney imaging and

also for blood flow studies.
The regulation and use of radioisotopes in today’s world

33

Thallium-201

Used in nuclear medicine for nuclear

cardiology and tumor detection.

Thallium-204

Measures the dust and pollutant levels on filter paper...and gauges the

thickness of plastics, sheet metal, rubber, textiles and paper.

Thoriated Tungsten

Used in electric arc welding rods in

construction, aircraft, petrochemical

and food processing equipment industries. They produce easier starting,

greater arc stability and less metal

contamination.

Thorium-229

Helps fluorescent lights last longer.

Thorium-230

Provides coloring and fluorescence in

colored glazes and glassware.

Courtesy of Management Information Systems, Inc.

Tritium

Major tool for biomedical research.

Used for life science and drug metabolism studies to ensure the safety

of potential new drugs...for self-luminous aircraft and commercial exit

signs...for luminous dials, gauges

and wrist watches...to produce luminous paint, and for geological prospecting and hydrology.

Uranium-234

Used in dental fixtures like crowns

and dentures to provide a natural

color and brightness.

Uranium-235

Fuel for nuclear power plants and

naval nuclear propulsion systems

...and used to produce fluorescent

glassware, a variety of colored glazes

and wall tiles.

Xenon-133

Used in nuclear medicine for lung

ventilation and blood flow studies.
Notes

34

NUREG/BR-0217 Rev. 1

APRIL 2000

U.S. Nuclear Regulatory

Commission

Washington, DC 20555-0001

Office of Public Affairs