1.1 What is ionizing radiation? |
1.2 How does radioactive material enter
and spread through the environment? |
1.3 How might I be exposed to ionizing
radiation? |
1.4 How can ionizing radiation enter and
leave my body? |
1.5 How can ionizing radiation affect
my health? |
1.6 How can ionizing radiation affect
children? |
1.7 How can families reduce the risk of
exposure to ionizing radiation? |
1.8 Is there a medical test to determine
whether I have been exposed to ionizing radiation? |
1.9 What recommendations has the federal
government made to protect human health? |
1.10 Where can I get more information? |
References |
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September 1999 |
Public Health Statement |
for |
Ionizing Radiation |
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This Public Health Statement is the
summary chapter from the Toxicological
Profile for ionizing radiation. It is one in a series
of Public Health Statements about hazardous substances and
their health effects. A shorter version, the ToxFAQs™,
is also available. This information is important because this
substance may harm you. The effects of exposure to any hazardous
substance depend on the dose, the duration, how you are exposed,
personal traits and habits, and whether other chemicals are
present. For more information, call the ATSDR Information
Center at 1-888-422-8737.
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This public health statement tells you
about ionizing radiation and the effects of exposure. It does
not tell you about non-ionizing radiation, such as microwaves,
ultrasound, or ultraviolet radiation.
Exposure to ionizing radiation can come
from many sources. You can learn when and where you may be
exposed to sources of ionizing radiation in the
exposure section below. One source of exposure is from
hazardous waste sites that contain radioactive waste. The
Environmental Protection Agency (EPA) identifies the most
serious hazardous waste sites in the nation. These sites make
up the National Priorities List (NPL) and are the sites targeted
for federal cleanup. However, it's unknown how many of the
1,467 current or former NPL sites have been evaluated for
the presence of ionizing radiation sources. As more sites
are evaluated, the sites with ionizing radiation may increase.
This information is important because exposure to ionizing
radiation may harm you and because these sites may be sources
of exposure.
When a substance is released from a large
area, such as an industrial plant, or from a container, such
as a drum or bottle, it enters the environment. This release
does not always lead to exposure. Even in the event that you
are exposed, it does not necessarily mean you will be harmed
or suffer long-term health effects from exposure to ionizing
radiation.
If you are exposed to ionizing radiation,
many factors determine whether you'll be harmed. These factors
include the dose (how much), the duration (how long), and
the type of radiation. You must also consider the chemicals
you're exposed to and your age, sex, diet, family traits,
lifestyle, and state of health.
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1.1
What is ionizing radiation? |
To explain what ionizing radiation is,
we will start with a discussion of atoms, how they come to
be radioactive, and how they give off ionizing radiation.
Then, we will explain where radiation comes from. Finally,
we will describe the more important types of radiation to
which you may be exposed. Of the different types and sources
of ionizing radiation, this profile will discuss the three
main types: alpha, beta, and gamma radiation.
The Atom. Before defining ionizing
radiation, it is useful to first describe an atom. Atoms are
the basic building blocks of all elements. We have models
of an atom that are supported by measurements. An atom consists
of one nucleus, made of protons and neutrons, and many smaller
particles called electrons. The electrons normally circle
the nucleus much like the planets or comets circle the sun.
The number of protons in the atom's nucleus determines which
element it is. For example, an atom with one proton is hydrogen
and an atom with 27 protons is cobalt. Each proton has a positive
charge, and positive charges try to push away from one another.
The neutrons neutralize this action and act as a kind of glue
that holds the protons together in the nucleus. The number
of protons in an atom of a particular element is always the
same, but the number of neutrons may vary. Neutrons add to
the weight of the atom, so an atom of cobalt that has 27 protons
and 32 neutrons is called cobalt-59 because 27 plus 32 equals
59. If one more neutron were added to this atom, it would
be called cobalt-60. Cobalt-59 and cobalt-60 are isotopes
of cobalt. Isotopes are forms of the same element, but differ
in the number of neutrons within the nucleus. Since cobalt-60
is radioactive, it is called a radionuclide. All isotopes
of an element, even those that are radioactive, react chemically
in the same way. Atoms tend to combine with other atoms to
form molecules (for example, hydrogen and oxygen combine to
form water). Radioactive atoms that become part of a molecule
do not affect the way the molecule behaves in chemical reactions
or inside your body.
What Ionizing Radiation Is. Ionizing
radiation is energy that is carried by several types of particles
and rays given off by radioactive material, x ray machines,
and fuel elements in nuclear reactors. Ionizing radiation
includes alpha particles, beta particles, x rays, and gamma
rays. Alpha and beta particles are essentially small fast
moving pieces of atoms. X rays and gamma rays are types of
electromagnetic radiation. These radiation particles and rays
carry enough energy that they can knock out electrons from
molecules, such as water, protein, and DNA, with which they
interact. This process is called ionization, which is why
it is named "ionizing radiation." We cannot sense ionizing
radiation, so we must use special instruments to learn whether
we are being exposed to it and to measure the level of radiation
exposure. The other types of electromagnetic radiation include
radiowaves microwaves, ultrasound, infrared radiation, visible
light, and ultraviolet light. These types of radiation do
not carry enough energy to cause ionization and are called
non-ionizing radiation. This profile will only discuss ionizing
radiation.
What Ionizing Radiation Is Not.
Ionizing radiation is not a substance like salt, air, water,
or a hazardous chemical that we can eat, breathe, or drink
or that can soak through our skin. However, many substances
can become contaminated with radioactive material, and people
can be exposed to ionizing radiation from these radioactive
contaminants.
How Does an Atom Become Radioactive?
An atom is either stable (not radioactive) or unstable
(radioactive). The ratio of neutrons to protons within the
nucleus determines whether an atom is stable. If there are
too many or too few neutrons, the nucleus is unstable, and
the atom is said to be radioactive. There are several ways
an atom can become radioactive. An atom can be naturally radioactive,
it can be made radioactive by natural processes in the environment,
or it can be made radioactive by humans. Naturally occurring
radioactive materials such as potassium-40 and uranium-238
have existed since the earth was formed. Other naturally occurring
radioactive materials such as carbon-14 and hydrogen-3 (tritium)
are formed when radiation from the sun and stars bombards
the earth's atmosphere. The elements heavier than lead are
naturally radioactive because they were originally formed
with too many neutrons. Human industry creates radioactive
materials by one of two different processes. In the first
process, a uranium or a plutonium atom captures a neutron
and splits (undergoes nuclear fission) into two radioactive
fission fragments plus two or three neutrons. In a nuclear
reactor, one of these "fission neutrons" is captured by another
uranium atom, and the fission process is repeated. In the
second process, stable atoms are bombarded either by neutrons
or by protons that are given a lot of energy in a machine
called an accelerator. The stable atoms capture these bombarding
particles and become radioactive. For example, stable cobalt-59,
found in the steel surrounding a nuclear reactor, is hit by
neutrons coming from the reactor and can become radioactive
cobalt-60. Any material that contains radioactive atoms is
radioactive material.
How Does a Radioactive Atom Give off
Ionizing Radiation? Because a radioactive atom is unstable,
at some time in the future, it will transform into another
element by changing the number of protons in the nucleus.
This happens because one of several reactions takes place
in the nucleus to stabilize the neutron-proton ratio. If the
atom contains too many neutrons, a neutron changes into a
proton and throws out a negative "beta" (pronounced bay' tah)
particle. If the atom contains too many protons, normally
a proton changes into a neutron and throws out a positive
"beta" particle. Some atoms that are more massive than lead,
such as radium, transform by emitting an "alpha" (pronounced
al'-fah) particle. Any excess energy that is left can be released
as "gamma" rays, which are the same as x rays. Other reactions
are also possible, but the final result is to make a radioactive
atom into a stable atom of a different element. For example,
each atom of cobalt-60 is radioactive because it has too many
neutrons. At some time in the future, one of its neutrons
will change into a proton. As it changes, the atom gives off
its radiation, which is a negative beta particle and two gamma
rays. Because the atom now has 28 protons instead of 27, it
has changed from cobalt into nickel. In this way, unstable
atoms of radioactive cobalt-60 give off radiation as they
transform into stable atoms of nickel-60.
How Long Can Radioactive Material
Give Off Ionizing Radiation? Theoretically, it gives off
ionizing radiation forever. Practically, however, after 10
half-lives, less than 0.1% of the original radioactivity will
be left and the radioactive material will give off infinitesimally
small amounts of ionizing radiation. The half-life is the
time it takes one-half of the radioactive atoms to transform
into another element, which may or may not also be radioactive.
After one half-life, ½ of the radioactive atoms remain;
after two half-lives, half of a half or 1/4 remain, then 1/8,
1/16, 1/32, 1/64, etc. The half-life can be as short as a
fraction of a second or as long as many billions of years.
Each type of radioactive atom, or radionuclide, has its own
unique half-life. For example, technetium-99m and iodine-131,
which are used in nuclear medicine, have 6-hour and 8-day
half-lives, respectively. The naturally occurring radionuclide,
uranium-235, which is used in nuclear reactors, has a half-life
of 700 million years. Naturally occurring potassium-40, which
is present in the body, has a half-life of 13 billion years
and undergoes about 266,000 radioactive transformations per
minute in the body. Thus, technetium-99m will remain radioactive
for 60 hours, and iodine-131 will remain radioactive for 3
months. On the other hand, long-lived naturally occurring
uranium and potassium will remain, practically speaking, radioactive
forever.
What Are the Three Types of Radiation?
The three main types of ionizing radiation are called alpha,
beta, and gamma radiation. These are named for letters of
the Greek alphabet, and they are often symbolized using the
Greek letters alpha (α), beta (β), and gamma (γ).
Alpha Radiation (or Alpha Particles).
This type of radiation can be called either alpha radiation
or alpha particles. Alpha radiation is a particle, consisting
of two protons and two neutrons, that travels very fast and
thus has a good deal of kinetic energy or energy of motion.
The two protons and neutrons make an alpha particle identical
to a helium atom, but without the electrons. Although it is
much too small to be seen with the best microscope, it is
large compared to a beta particle. The protons give it a large
positive charge that pulls hard at the electrons of other
atoms it passes near. When the alpha particle passes near
an atom, it excites its electrons and can pull an electron
from the atom, which is the process of ionization. Each time
the alpha particle pulls an electron off from an atom in its
path, the process of ionization occurs. With each ionization,
the alpha particle loses some energy and slows down. It will
finally take two electrons from other atoms at the end of
its path and become a complete helium atom. This helium has
no effect on the body. Because of their large mass and large
charge, alpha particles ionize tissue very strongly. If the
alpha particle is from radioactive material that is outside
the body, it will lose all its energy before getting through
the outer (dead) layer of your skin. This means that you can
only be exposed to alpha radiation if you take radioactive
material that produces alpha radiation into your body (for
example, if you breathe it in or swallow it in food or drink).
Once inside the body, this radioactive material can be mixed
in the contents of the stomach and intestines, then absorbed
into the blood, incorporated into a molecule, and finally
deposited into living tissue such as the bone matrix. The
alpha particles from this radioactive material can cause damage
to this tissue.
Beta Radiation (or Beta Particles).
This type of radiation can be called either beta radiation
or beta particles. Beta particles are high-energy electrons
that some radioactive materials emit when they transform.
Beta particles are made in one of two ways, depending on the
radioactive material that produces them. As a result, they
will have either a positive charge or a negative charge. Most
beta particles are negatively charged. They are much lighter
and much more penetrating than alpha particles. Their penetrating
power depends on their energy. Some, such as those from tritium,
have very little energy, and can't pass through the outer
layer of dead skin. Most have enough energy to pass through
the dead outer layer of a person's skin and irradiate the
live tissue underneath. You can also be exposed to beta radiation
from within if the beta- emitting radionuclide is taken into
the body. A beta particle loses its energy by exciting and
ionizing atoms along its path. When all of its kinetic energy
is spent, a negative beta particle (negatron) becomes an ordinary
electron and has no more effect on the body. A positive beta
particle (positron) collides with a nearby negative electron,
and this electron-positron pair turns into a pair of gamma
rays called annihilation radiation, which can interact with
other molecules in the body.
Gamma Radiation (or Gamma Rays).
This type of radiation can be called either gamma radiation
or gamma rays. Unlike alpha and beta radiation, gamma radiation
is not a particle, but is a ray. It is a type of light you
cannot see, much like radio waves, infrared light, ultraviolet
light, and x rays. When a radioactive atom transforms by giving
off an alpha or a beta particle, it may also give off one
or more gamma rays to release any excess energy. Gamma rays
are bundles of energy that have no charge or mass. This allows
them to travel very long distances through air, body tissue,
and other materials. They travel so much farther than either
alpha or beta radiation that the source of the gamma rays
doesn't have to be inside the body or near the skin. The gamma
ray source can be relatively far away, like the radioactive
materials in nearby construction materials, soil, and asphalt.
A gamma ray may pass through the body without hitting anything,
or it may hit an atom and give that atom all or part of its
energy. This normally knocks an electron out of the atom (and
ionizes the atom). This electron then uses the energy it received
from the gamma ray to ionize other atoms by knocking electrons
out of them as well. Since a gamma ray is pure energy, once
it loses all its energy it no longer exists.
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1.2
How does radioactive material enter and spread through the environment? |
Radioactive material can be released
to the air as particles or gases as a result of natural forces
and from human industrial, medical, and scientific activities.
Everyone, with no exception, is exposed to ionizing radiation
that comes from natural sources, such as cosmic radiation
from space and terrestrial radiation from radioactive materials
in the ground. Ionizing radiation can also come from industrially
produced radioactive materials (such as iridium-192); nuclear
medicine (such as thyroid cancer treatment with iodine-131
and thyroid scans using iodine-125, or bone scans using technetium-99m);
biological and medical research using carbon-14, tritium,
and phosphorus-32; the nuclear fuel cycle (producing fission
products such as cesium-137 and activation products such as
cobalt-60); and production and testing of nuclear weapons.
Radioactive material released into the air is carried by the
wind and is spread by mixing with air. It is diluted in the
atmosphere and can remain there for a long time. When the
wind blows across land contaminated with radioactive materials,
radioactive particles can be stirred up and returned to the
atmosphere. Radioactive material on the ground can be incorporated
into plants and animals, which may later be eaten by people.
Water can contain man-made and naturally
occurring radioactive materials that it dissolves from the
soil it passes over or through. Rain and snow also wash man-made
and naturally occurring radioactive material out of the air.
Radioactive material may be added to water through planned
or accidental releases of liquid radioactive material from
sources such as hospitals, research universities, manufacturing
plants, or nuclear facilities. Radioactive material can also
reach surface waters when airborne radioactive materials settle
to the earth or are brought down by rain or snow, and when
soil containing radioactive material is washed away into a
river or lake. The movement of liquid radioactive material
is limited by the size of the bodies of water into which the
radioactive materials have drained. Like silt, some radioactive
material may settle along the banks or in the bottoms of ponds
and rivers. In public health and ecological contexts, it is
sometimes important to distinguish between dissolved radioactivity
and radioactivity bound to suspended or settled solid particles.
Radioactive material may also concentrate in aquatic animals
and plants. Eventually, radioactive material in liquid runoff
that goes into rivers and streams may reach the oceans (there
are approximately one million radioactive transformations
per minute of the naturally occurring radioactive potassium
in one cubic meter of ocean water).
Radioactive material moves very slowly
in soil compared to its speed of movement in air and water.
Radioactive material will often stick to the surface of the
soil. The organic material in soils can bind radioactive material,
which slows its movement through the environment. If crops
are watered with water containing radioactive material, the
radioactive material may be taken up through the roots of
the plant or may contaminate the outside of the plant. The
plants may then be eaten by both animals and people. Radioactive
materials that occur naturally in the soil (uranium, radium,
thorium, potassium, tritium, and others) are also taken up
by plants, and become available for intake by animals and
people.
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1.3
How might I be exposed to ionizing radiation? |
The earth is continually irradiated with
low levels of ionizing radiation, so all animals, plants,
and other living creatures are exposed to small amounts of
ionizing radiation from several sources every day.
Figure 1 shows that most of your radiation
dose comes naturally from the environment. Smaller portions
come from medicine, consumer products and other sources.
Figure 2 is another breakdown of the
sources of radiation dose to the average American. The natural
background levels (82%) shown in Figure 1-1 include the radon,
terrestrial, cosmic, and natural internal sources shown in
Figure 1-2. Most of your daily radiation dose is from radon
(55%), which is found in all air. Higher levels are normally
found indoors (especially in the basement).
Figure 3 shows that indoor levels of
radon vary depending on where you live. Higher levels can
be found in underground areas, such as mines.
You are always exposed to radiation from
cosmic sources (mostly from outer space, some from the sun,
8%), terrestrial sources (rocks and soil, 8%), and natural
internal sources (radioactive material normally inside your
body, 10%). You may also be exposed to radiation from x ray
exams (11%), nuclear medicine exams such as thyroid scans
(4%), and consumer products including TV and smoke detectors
(3%), as well as other sources.
Less than 1% of the total ionizing radiation
dose to people living in the United States comes from their
jobs, nuclear fallout, the nuclear fuel cycle, or other exposures.
However, people in some types of jobs may have higher doses
(pilots and flight attendants, astronauts, industrial and
nuclear power plant workers, x ray personnel, medical personnel,
etc.). Some groups of people have been exposed to higher-than-
normal levels of ionizing radiation from weapons testing,
and some individuals from accidents at nuclear facilities
or in industry.
Not everyone will be exposed to every
source or the same percentage of radiation shown in Figure
2. Since the percentages shown in Figure 2 are averages, half
of the population will receive greater doses and half will
receive smaller doses from the several sources shown in the
figure. For example, if you are not regularly x rayed, you
may receive less total radiation dose than what is shown.
However, if you live in a town or city at a high altitude,
you may receive a greater radiation dose from outer space
cosmic rays than someone who lives in a town or city near
the ocean at sea-level. Table 1 shows you that where you live
and what you do determines how much ionizing radiation you
will receive.
Table 1-1. Approximate Doses of
Ionizing Radiation to Individuals
Activity |
Approximate doses of radiation received |
Comments |
Average American exposure to ionizing
radiation |
Total yearly dose |
360 mrem/yr
(3.6 mSv/yr) |
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From natural sources |
300 mrem/yr
(3.0 mSv/yr) |
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From man-made sources |
60 mrem/yr
(0.6 mSv/yr) |
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From nuclear power |
Less than 1 mrem/yr
(<0.01 mSv/yr) |
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Approximate doses of ionizing radiation
(cosmic + terrestrial) for different locations |
Kerala, India, resident |
1300 mrem/yr
(13 mSv/yr) |
Concentrated radioactive material in
the soil |
Colorado state resident |
179 mrem/yr
(1.79 mSv/yr) |
High altitude above sea level |
Boston, Massachusetts, resident |
100 mrem/yr
(1 mSv/yr) |
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Louisiana state resident |
92 mrem/yr
(0.92 mSv/yr) |
Low altitude above sea level |
Approximate doses of ionizing radiation
above background radiation and some activities |
Anyone near a patient released after a nuclear medicine
test. |
Less than 500 mrem/patient
(5 mSv/patient) |
Guidance for medical facilities. Quantity
depends on the quantity of radioactive material. |
A person who works inside a nuclear power plant |
< 300 mrem/yr
(<3 mSv/yr) |
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A person who gets a full set of dental x rays |
40 mrem
(0.4 mSv) |
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A flight attendant flying from New York to Los Angeles |
5 mrem/flight
(0.05 mSv/flight) |
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Watching a color TV set |
2-3 mrem/yr
(0.02-0.03 mSv/yr) |
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A person who lives directly outside of a nuclear power
plant |
1 mrem/yr
(0.01 mSv/yr) |
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A person who lives in a multi-storied apartment building |
~1 mrem/yr for each 5 stories above
the ground floor
(<0.01 mSv/yr) |
Difference between Los Angeles and
Denver = 87 mrem/5000 feet = 2 mrem/100 feet = 1 mrem/5
stories |
A person who watches a truck carrying nuclear waste
pass by |
Less than 0.1 mrem/truck
(0.001 mSv) |
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"Dose" is a broad term that is often
used to mean either absorbed dose, or dose equivalent, depending
on the context. The absorbed dose is measured in both a traditional
unit called a rad and an International System (S.I.) unit
called a gray (Gy). Both grays and rads are physical units
(1 Gy = 100 rad) that measure the concentration of absorbed
energy. The absorbed dose is the amount of energy absorbed
per kilogram of absorber. Physical doses from different radiations
are not biologically equivalent. For this reason, a unit called
the dose equivalent, which considers both the physical dose
and the radiation type, is used in radiation safety dosimetry.
The unit of dose equivalent is called the rem in traditional
units and the sievert (Sv) in S.I. units (1 rem = 0.01 Sv).
For beta and gamma radiation, 1 rad = 1 rem (1 gray = 1 sievert).
For alpha radiation, however, 1 rad = 20 rem (1 gray = 20
sievert). Small radiation doses can be expressed using small
dose units such as the millirem (mrem) and the millisievert
(mSv), where 1 mrem = 0.001 rem and 1 mSv = 0.001 Sv.
The average annual dose to a person in
the United States is about 360 mrem (3.6 mSv). An individual's
exact dose depends on several factors, such as the natural
background where the person lives, and the person's medical
history and occupational experience with sources of radiation.
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1.4
How can ionizing radiation enter and leave my body? |
Ionizing radiation exposure can occur
from a radiation source outside of the body. Exposure can
also occur as a result of taking radioactive material into
your body. The answer to the question of how you can be exposed
to ionizing radiation can be broken into two parts. The first
paragraph below describes ionizing radiation that comes from
a source outside your body and some distance away (external
radiation). The second paragraph describes ionizing radiation
that comes from a source inside your body (internal radiation).
External radiation comes from
natural and man-made sources of ionizing radiation that are
outside your body. Part of the natural radiation is
cosmic radiation from space. The rest is given off by radioactive
materials in the soil and building materials that are around
you. As a result of human activities, higher levels of natural
radioactive material are left in products or on the land.
Examples of such activities are manufacturing fertilizer,
burning coal in power plants, and mining and purifying uranium.
Ionizing radiation from human activities adds to your external
radiation exposure. Some of this radiation is given off by
x ray machines, televisions, radioactive sources used in industry,
and patients who have had recent nuclear medicine tests and
therapy. The rest is given off by man-made radioactive materials
in consumer products, industrial equipment, atom bomb fallout,
and to a smaller extent by hospital waste and nuclear reactors.
Gamma rays are the main type of ionizing radiation that are
of concern when you are exposed to external sources of ionizing
radiation. Gamma rays (like x rays) are special bundles of
light energy that you cannot see, feel, or smell. Gamma rays
from natural and man-made sources pass through your body just
like x rays do, at the speed of light. Gamma rays may pass
directly through your body without hitting anything. When
one gamma ray hits a cell, it leaves a small bit of energy
behind that can cause damage. Other types of ionizing radiation,
like alpha and beta particles, hit your body but normally
do not have enough energy to get inside to harm you. Your
external radiation dose depends on the amount of energy that
ionizing radiation gives to your body as it passes through.
Exposure to external radiation does not make you radioactive.
The average yearly dose from external radiation in the United
States is about 100 mrem per person (1 mSv/person).
Internal radiation is ionizing
radiation that natural and man-made radioactive materials
give off while they are inside your body. You take
radioactive materials into your body every day since they
are in the air you breathe, the food you eat, and the water
you drink. Examples of natural radioactive materials that
enter, reside in, and leave your body every day include potassium-40,
carbon-14, radium, and radon. Man-made radioactive materials
also get into your body from the decreasing amounts of fallout
from past nuclear weapons testing. Sometimes, natural conditions
or industrial activities concentrate radioactive materials.
If you are exposed to these, you will take in more radioactive
material. Low amounts of material that act as sources of ionizing
radiation may also be put into your body for medical purposes
to test for or treat some types of disease, such as cancer.
Scientists and clinicians have made sure that the benefits
of exposing you to ionizing radiation far outweigh any bad
health effects you may get from the ionizing radiation by
itself. (Medical tests use small amounts of radiation or radioactive
material, but some radiotherapy uses large doses that are
beneficial to the patient.) Hospitals, coal-fired electricity
generating plants, and nuclear reactors release radioactive
materials in ways that keep your dose low. Radioactive materials
build up in your body if you take them in faster than they
leave in urine and feces and by radioactive transformation.
If the internally deposited radioisotope is short lived and
decays before the body eliminates it, then, of course, it
will disappear faster from the body than by biological elimination
alone. Thus, retention or elimination of internally deposited
radioisotopes is measured by the effective half-life, which
considers the combined effect of biological elimination and
radioactive decay.
Internally deposited radioisotopes may
emit gamma rays, beta particles, or alpha particles, depending
on the isotope. Many gamma rays escape your body without hitting
anything. When a gamma ray does hit a cell, it transfers energy
to the cell. When all their energy is transferred, they vanish.
Alpha and beta particles travel short distances, giving energy
to cells they hit. They lose energy and quickly come to a
stop. Their energy is totally absorbed inside your body. When
alpha particles come to a stop, they become helium that you
breathe out later. When beta particles come to a stop, they
become electrons and attach to atoms near them. Your internal
dose is a measure of the energy deposited by all the ionizing
radiation that is produced inside your body. The average yearly
dose in the United States from internal radiation is about
260 mrem per person (2.6 mSv/person).
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1.5
How can ionizing radiation affect my health? |
How radiation affects your health depends
on the size of the radiation dose. Scientists have been studying
the effects of ionizing radiation in humans and laboratory
animals for many years. Studies so far have not shown that
the low dose of ionizing radiation we are exposed to every
day causes us any harm. We do know that exposure to massive
amounts of ionizing radiation can cause great harm, so it
is wise to not be exposed to any more ionizing radiation than
necessary.
Overexposure to high amounts of ionizing
radiation can lead to effects like skin burns, hair loss,
birth defects, cancer, mental retardation (a complex central
nervous system functional abnorm ality), and death. The dose
determines whether an effect will be seen and its severity.
For some effects such as skin burns, hair loss, sterility,
nausea, and cataracts, there is a certain minimum dose (the
threshold dose) that must be exceeded to cause the effect.
Increasing the size of the dose after the threshold is exceeded
makes the effect more severe. Psychological stress has been
documented in large populations exposed to small doses of
radiation (Three Mile Island and Chernobyl). Neurological
injury (CNS syndrome) resulting in compromised mental function
has also been documented in individuals exposed to several
thousand rads of ionizing radiation.
Ionizing radiation is called a carcinogen
because it may also increase your chance of getting cancer.
Increasing the size of the dose increases your chance of getting
cancer. Scientists base radiation safety standards on the
assumption that any radiation dose, no matter how small, carries
with it a corresponding probability of causing a cancer. This
is called a "zero threshold" dose response relationship. Cancers
that are actually caused by radiation are completely indistinguishable
from those from other causes, so we can never be certain whether
any individual cancer was not caused by radiation. To determine
how likely it is that a certain dose of radiation will cause
cancer, scientists measure the radiation dose to a group of
exposed people, like the Japanese atomic bomb survivors. Then
they compare the frequency of cancers (the observation period
for cancer extends over decades) in this exposed group with
a similar group of people who were not exposed. They also
look at factors like age, sex, and time since the exposure
ended. Finally, they calculate risk factors for various cancer
types. Using these factors, it is possible to estimate the
chance of getting cancer from a dose of radiation. Even though
they assume a zero threshold, researchers have not actually
seen an increase in cancer frequency for people in the exposed
Japanese group who had a radiation dose below 20 rad (0.2
Gy). No increase in any type of leukemia has been found in
people whose radiation dose was below 10–40 rad (0.1–0.4 Gy).
The effects of internally deposited radioactive
material are similar to those of external radiation. The effects
depend on the size of the dose and factors like your sex and
age when you were exposed. The radiation absorbed dose, in
turn, depends on the radioactive material, the amount of activity,
the type and energy of the radiation, the effective half-life
of the radioactive material, its chemical form, how it was
taken into your body, and how quickly it leaves your body.
Many people are exposed to radiation
and radioactive materials used in medical testing and therapy.
Radiation treatments for medical reasons carry the same risk
as radiation from other sources. As with any medical treatment,
the potential health benefits should be balanced against the
potential harmful health effects.
One way to better understand the effects
of radiation is to study its effects on test animals. Without
laboratory animals, scientists would lose a basic method to
get information needed to make informed decisions to protect
public health. Scientists have the responsibility to treat
research animals with care and compassion. Laws today protect
the welfare of research animals, and scientists must comply
with strict animal care guidelines.
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1.6
How can ionizing radiation affect children? |
This section discusses potential health
effects from exposures during the period from conception to
maturity at 18 years of age in humans. Potential effects on
children resulting from exposures of the parents are also
considered.
Like adults, children are exposed to
small background amounts of ionizing radiation that comes
from the soil around where they live, in the food and water
that they eat and drink, in the air that they breathe, and
from sources that reach earth from space. How much background
radiation you receive depends on where you live. Some places
naturally have more than others. There are no reports that
say exposure to background levels of ionizing radiation causes
health effects in children or adults.
If a pregnant woman is exposed to high
levels of ionizing radiation, it is possible that her child
may be born with some brain abnormalities. There is an 8-week
period during early pregnancy when an unborn child is especially
sensitive to the effects of higher than normal levels of ionizing
radiation. As the levels of ionizing radiation increase, so
does the chance of brain abnormalities. These abnormalities
may eventually result in small head size, decreased intelligence
as measured by Intelligence Quotient (IQ) tests, and other
defects. These effects are not reversible.
A child will be exposed to small amounts
of radiation from the environment all during prenatal development
and throughout its life. There are no reports that say children
suffer health effects from normal amounts of background radiation.
If children are exposed to higher than background levels of
ionizing radiation, they are likely to have the same possible
health effects as adults exposed to similar levels.
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1.7
How can families reduce the risk of exposure to ionizing radiation? |
If your doctor finds that you have been
exposed to significant amounts of ionizing radiation, ask
whether your children might also be exposed. Your doctor might
need to ask your state health department to investigate.
The best way to reduce your risk of exposure
to higher than background amounts of radiation is to not let
yourself be exposed at all. However, this is not always possible
or sensible. A common way to be exposed to ionizing radiation
is by receiving an x ray, but a few x rays every year will
not hurt you. When you or your children receive an x ray,
be sure to correctly wear any protective garments that are
provided. The technician will make sure that only the area
that needs to be x rayed will be exposed to the x ray beam.
It may be necessary to inject you with
a chemical that has some amount of radioactive material in
it to help a doctor diagnose or treat a disease. Many studies
have shown that these drugs, used correctly, will not harm
you. Be sure to follow the doctor's directions after you have
been treated with these drugs.
Many places make or use various types
of radioactive material or ionizing radiation for medical
or research purposes. If you visit one of these facilities,
be sure to follow all of the recommended safety precautions.
Do not go into unauthorized areas. You may be asked to wear
a special device on your shirt that records the amount of
ionizing radiation you are exposed to while in the facility.
This is a safety precaution. Do not put it in your pocket
or let someone else wear it.
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1.8
Is there a medical test to determine whether I have been exposed
to ionizing radiation? |
There are no easy or accurate medical
tests to determine whether you have been exposed to low doses
of ionizing radiation, but tests are available for determining
whether you have been exposed to radioactive material.
Tests for Recent Exposure to Ionizing
Radiation. A great degree of overexposure is necessary
to cause the clinical signs or symptoms of radiation exposure.
In the absence of clinical signs or symptoms there are two
kinds of tests scientists use to see if you have been overexposed
to ionizing radiation; they look for changes in blood cell
counts and changes in your chromosomes. If you are exposed
to no more than 10 rad (0.1 Gy) of ionizing radiation, there
are no detectable changes in blood cell counts. The most sensitive
measure of radiation exposure involves a study of your chromosomes.
This is a special test for doses that are too low to produce
clinically observable signs or symptoms; this test may be
useful for doses greater than about 3 times the maximum annual
permissible dose for radiation workers. Changes in the white
blood cell count may be seen in people whose doses exceeded
about 5 times the occupational maximum permissible annual
dose. Radiation doses at or above these levels can be reliably
estimated using these two special tests.
Tests for Radioactive Material Inside
Your Body. Scientists can also examine your blood, feces,
saliva, urine, and even your entire body to see if measurable
amounts of radioactive material are being excreted from your
body. Different tests are used for different types of radioactive
material. Several types of instruments are available to look
for each type of radiation. These instruments are not available
at your doctor's office. They are normally large, heavy, and
available only in laboratories. Equipment usually consists
of a "detector," electrical cables, and a "processor." The
detector contains material sensitive to one or more types
of radiation, so the detector is chosen based on the type
of radiation to be measured. Alpha, beta, and gamma radiation
have different energies that depend upon the radioactive isotope
from which they come. By determining the type and energy of
the radiation, scientists can tell which radioisotope is on
your skin or inside your body.
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1.9
What recommendations has the federal government made to protect
human health? |
Recommendations and regulations are periodically
updated as more information becomes available. For the most
current information, check with the federal or state agency
or organization that provides it.
The current federal and state regulations
limit radiation workers' doses to 0.05 Sv/year (5 rem/year).
The limit for the unborn child of a female radiation worker
is 0.005 Sv (0.5 rem) per 9-month gestation period. For the
general public, the limit is 0.001 Sv/year (0.1 rem/year),
with provisions for a limit of 0.005 Sv/year (0.5 rem/year)
under special circumstances. The public dose limit is set
at least 10 times lower than the occupational limit to give
the public an extra margin of safety. A factor of 10 is also
used for public protection in other industries.
We have seen health effects from very
high doses of ionizing radiation, but not at normal everyday
levels. To be cautious, scientists and regulating agencies
assume that there could be some harmful effects at any dose,
no matter how small. Because ionizing radiation has the potential
to cause harmful health effects in overexposed people, regulations
and guidelines have been established for ionizing radiation
by state, national, and international agencies. The basic
philosophy of radiation safety is to allow only a reasonable
risk of harm using the concept of "as low as reasonably achievable"
(ALARA). Some regulations and recommendations for ionizing
radiation include the following:
Radiation protection standards for radiation
workers and members of the public are recommended by the International
Commission on Radiological Protection (ICRP) and the National
Council on Radiation Protection and Measurements (NCRP). These
standards are not regulations, but they provide the scientific
basis for the making of regulations by federal agencies. The
ICRP and NCRP are authoritative bodies that analyze current
scientific and epidemiological data and make recommendations
to government and non-government organizations that set standards.
ICRP and NCRP do not issue standards themselves.
Federal agencies, such as the EPA, the
Nuclear Regulatory Commission (NRC), and the Department of
Energy (DOE), as well as individual states are responsible
for making federal and state regulations about exposure to
ionizing radiation. The NRC regulates nuclear power plant
operations and regulates the use of radioactive material in
research and medical applications. The DOE has issued employee
dose limits for its facilities.
The EPA is responsible for federal radiation
protection guidance for environmental radiation standards
and regulations to implement specific statutory requirements,
such as the Safe Drinking Water Act and the Clean Air Act.
Natural background radiation, of course, cannot be regulated
but EPA recommends that the concentration of indoor radon
not exceed 4 picocuries per liter (4 pCi/L) of air. EPA's
National Emission Standards for Hazardous Air Pollutants (NESHAPs)
contain regulations that limit the dose from radionuclides
released to the air to 0.1 mSv/year (10 mrem/year). The EPA
sets limits on the maximum acceptable concentration of radionuclides
in public drinking water supplies. Based on the Safe Drinking
Water Act, the EPA has issued drinking water standards for
radionuclides, which include dose limits of 0.04 mSv/year
(4 mrem/year) for man-made sources of beta and gamma emitters.
EPA also sets limits on several alpha emitters in drinking
water, such as radium and radon.
The NRC regulations apply to all types
of ionizing radiation that are emitted from special nuclear
material (such as nuclear reactor fuel) and from by-product
material (materials made radioactive in the use of special
nuclear material), and from source material (material from
which nuclear fuel is made).The NRC sets limits on the total
dose of ionizing radiation above background from these sources.
It also sets limits for the amounts and concentrations of
radioactive material that will give these doses if taken into
the body. These are called Annual Limits on Intake (ALI) and
derived air concentrations (DAC).
The NRC has also issued a standard for
cleaning up sites contaminated with radioactive materials.
It requires that the radiation dose to the public from these
sites will not be more than 0.25 mSv per year (25 mrem per
year).
Radiation doses from procedures used
by licensed physicians in diagnosis and treatment of disease
is not limited by regulations. However, physicians and medical
technicians must be specially trained and licensed to use
radiation-producing machines and licensed to use radioisotopes
for these purposes. They are required to limit exposures to
the members of the public who are inside their facilities
to 100 mrem per year, which is the same level as required
by the NRC. Also, patients with radioactive materials inside
their bodies from the treatment are kept until it is likely
that they will not expose anyone around them to more than
0.5 mSv (500 mrem) from that radioactive material.
States also regulate radioactive materials
and other sources of radiation that are not regulated by the
NRC. These include sources of natural radioactivity, such
as radium, and radiation-producing machines, such as x ray
machines and radioactive material produced by particle accelerators.
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1.10
Where can I get more information? |
If you have any more questions or concerns, please contact
your community or state health or environmental quality department or:
Agency for Toxic Substances and Disease Registry
Division of Toxicology
1600 Clifton Road NE, Mailstop F-32
Atlanta, GA 30333
Information line and technical assistance:
Phone: 888-422-8737
FAX: (770)-488-4178
ATSDR can also tell you the location of occupational and environmental health
clinics. These clinics specialize in recognizing, evaluating, and treating illnesses
resulting from exposure to hazardous substances.
To order toxicological profiles, contact:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Phone: 800-553-6847 or 703-605-6000
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References |
Agency for Toxic Substances and Disease
Registry (ATSDR). 1999. Toxicological
profile for ionizing radiation. Atlanta, GA: U.S. Department
of Health and Human Services, Public Health Service.
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