Frequently
Asked Questions about Health Effects of Low Doses of Radiation
What
is radiation?
What
are examples of ionizing radiation?
What
are examples of non-ionizing radiation?
Are
there beneficial health effects from exposure to ionizing radiation?
How
do we describe background radiation?
What
is a low dose of radiation?
What
is LET?
What
is radiation dose?
Are
there health effects from radiation?
Will
I get cancer if I am exposed to ionizing radiation?
What
are the genetic effects of ionizing radiation?
Will
exposure to an unborn child cause defects or death?
How
can cell and molecular research help in understanding the hazards
from radiation?
What
is a "dirty bomb"?
Will
I die from the bomb?
How
do I know if I have been exposed?
What
can I do to protect myself if I am close to a "dirty bomb"?
How
long will the radiation stay in the area? When can I go back
to my home?
What
is depleted Uranium?
Is
depleted uranium a serious radiation problem with potential
to produce cancer?
How
do we detect the presence of radiation?
What is 210Po ?
Were public health hazards associated with the 210Po contamination of the environment by Mr. Alexander Litvinenko?
- WHAT
IS RADIATION?
Radiation
is a form of energy. There are two basic types of radiation,
ionizing and non-ionizing radiation. The difference between
these two types is the amount of energy they have. Ionizing
radiation is high-energy radiation that has the ability to break
chemical bonds, cause ionization and produce free radicals that
can result in biological damage. Non-ionizing radiation does
not have enough energy to cause ionization but disperses energy
through heat and increased molecular movement. Health effects
from radiation have been a concern since their discovery.
Reference:
E.J. Hall (2000) Radiobiology for the Radiologist, Fifth Addition,
Lippincott Williams and Wilkins, Health Physics Web Site: http://hps.org/publicinformation/ate/faqs/whatisradiation.html
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What
are examples of ionizing radiation?
Ionizing
radiation consists of both particles and electromagnetic radiation.
The particles are further classified as electrons, protons,
neutrons and alpha particles, depending on their atomic characteristics.
The most common electromagnetic radiation with enough energy
to produce ions, break chemical bonds and alter biological function
are x-rays and gamma rays. Exposure to such radiation can cause
cellular and molecular changes such as mutations, chromosome
aberrations and cell killing. At high doses, it is well-established
that ionizing radiation is capable of increasing the cancer
rate in exposed populations at low doses it is not possible
to detect changes in cancer frequency. Studies on the health
effects of ionizing radiation have been conducted with each
of these types of radiation, delivered over a very wide range
of exposures and doses, and the effects evaluated at every level
of biological organization from the molecular to whole human
populations. These studies have resulted in extensive information
on the health effects produced by high doses from ionizing of
radiation. Studies at lower doses are currently being conducted
as new tools become available to both deliver the radiation
and study the response of cells and molecules. This research
has resulted in some very interesting results that suggest that
low doses of ionizing radiation with matter triggers many biological
responses that were not predicted from past experience. These
results include bystander effects, changes in the spectrum of
gene activation, adaptive responses and genomic instability.
All these are discussed further in the cited review papers.
Morgan, W.F. (2003) Non-targeted and delayed effects of exposure
to ionizing radiation: I. Radiation-induced genomic instability
and bystander effects In vitro. Radiation Research
159:567-580.
Morgan,
W.F. (2003) Non-targeted and delayed effects of exposure to
ionizing radiation: II. Radiation-Induced genomic instability
and bystander effects In vivo, Clastogenic factors
and transgenerational effects. Radiation Research 159:581-596.
Redpath, J.L., Lu, Q., Lao, X., Molloi, S., and Elmore, E. (2003)
Low doses of diagnostic energy X-rays protect against neoplastic
transformation In vitro. Int. J. Radiation. Biol.
79(4):235-240.
http://hps.org/publicinformation/ate/faqs/radiationtypes.html
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What
are examples of non-ionizing radiation?
Examples
of non-ionizing radiation include radio-waves, microwaves, radar,
microwaves and low energy light. Since such radiation is not
able to break chemical bonds the biological responses to this
exposure are not related to events such as mutations or chromosome
aberrations but are related to physiological changes. There
is extensive research on these types of radiation and discussion
as to whether they can cause adverse biological changes that
result in the formation of cancer. There are biological changes
induced by such radiation, but it has not been possible to establish
a strong link between these exposures and an increased cancer
risk.
National Academy of Sciences Report, Possible health effects
of residential electric and magnetic fields. www.nas.edu
http://www.osha.gov/SLTC/radiation_nonionizing/index.html
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Are
there beneficial health effects from exposure to ionizing radiation?
There
are many beneficial effects from the use of ionizing radiation.
Radiation is widely used in medicine for diagnosis and treatment
of many diseases. It has been estimated that there are more
than 200 million x-rays given each year in the United States
to diagnose and evaluate diseases or accidents. World-wide,
this number has been estimated at about 2 billion/year. Because
of the ability of radiation to kill cells, it has also been
widely used in cancer therapy. There are about 5.5 million people
treated each year to cure cancer. The use of radiation is a
very important tool in our health care system and has produced
great health benefits. However, excessive use of radiation in
medicine and the development of new techniques that deliver
more radiation that may be needed for proper diagnosis remains
as a concern for potential increased cancer risk. Extensive
research is being conducted to determine if there are health
benefits as well as adverse health effects from exposure to
low doses of ionizing radiation. To date the assumptions remain
that there is a linear relationship between the induction of
adverse health effects and exposure to radiation regardless
of the radiation dose. This assumption is the subject of active
discussion in the scientific community with some scientists
suggesting that there hormetic, adaptive or beneficial effects
that may decrease cancer risk below that predicted by the linear
extrapolation from high doses. If such effects exist it could
change the perception of risk associated with very low doses
of radiation. This is an area of active research.
NCRP 136, Belle NewsLetter (www.belleonline.com), Hall presentation,
World Congress on Radiation Risk, Brussels, Belgium, 2003.
Brenner,
D.J., Elliston, C.D., Hall, E.J., and Berdon W.E. (2001)
Estimated risks of radiation-induced fatal cancer from pediatric
CT, AJR 289-296.
http://www.physics.isu.edu/radinf/qanda.htm#use
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How
do we describe background radiation?
Natural
background radiation is the radiation exposure or dose that
is received daily from normal sources. Natural background radiation
comes from cosmic radiation, internally deposited radioactive
materials in the body, and radiation such as radon from environmental
sources such as soil and granite. The average natural background
radiation in the United States is about 300 mrems or 3.0 mSv
per year with the radon exposure being responsible for about
half of the total. There is a wide range of background radiation
(about a factor of 10 from the highest to the lowest) in different
regions of the U.S. In some regions of the world the background
radiation is more than a thousand times higher than the average
background level in the U.S. To date there have been no demonstrated
health effects due to the variability in background radiation.
There is also man made background radiation from nuclear weapons,
nuclear accidents, production of nuclear power and the use of
radioactive materials in consumer products. The estimated average
human exposure from man made background radiation is about 70
mrem/year. A complete description of background radiation can
be found in NCRP report 94.
NCRP National Council on Radiation Protection and Measurements,
1987. Exposure of the population in the United States and Canada
from natural background radiation. NCRP Report No.
94. Issued December 30, 1987. Bethesda, Maryland. National Council
on Radiation Protection and Measurements.
http://hps.org/publicinformation/ate/cat10.html
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What
is a low dose of radiation?
There are
two realistic definitions of a low dose of radiation. One is
a dose below which it is not possible to detect adverse health
effects. This level has been set by ICRP to be at 20 rads, 20,000
mrads or 0.2 Gy, 200 mGy. Others suggest that this level is
much lower and may be as low as 1 rad. Another definition of
a low dose of radiation would be the level of radiation that
we are exposed to from natural background radiation. In the
U.S. this dose ranges from 75 - 1000 mrads with a mean of 370
mrads, 0.37 rads or 3.7 mGy. This dose does not include exposure
to medical procedures.
NCRP National Council on Radiation Protection and Measurements,
1987. Exposure of the population in the United States and Canada
from natural background radiation. NCRP
Report No. 94. Issued December 30, 1987. Bethesda, Maryland.
National Council on Radiation Protection and Measurements.
This Web Site, Slide Show and Gallery Background pictures.
http://hps.org/publicinformation/ate/cat25.html#137
http://hps.org/publicinformation/ate/q87.html
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What
is LET?
Each type
of radiation has a characteristic atomic make up and can be
delivered over a range of different energies. As the radiation
interacts with matter, it loses its energy through interactions
with the atoms that it associates with. The average amount of
energy that is lost over a defined distance, for example the
energy deposited in ten cells, is known as the Linear Energy
Transfer (LET). The distribution of energy in cells has a marked
influence on the amount of biological damage that is done by
a fixed amount of radiation. Some types of radiation, like alpha
particles, deposit a large amount of energy in a small distance
and are called high-LET radiation. For alpha particles a high-LET
radiation all the particles energy can be deposited in a few
cells. Other radiation types like x-rays or gamma rays penetrate
tissues very easily and for any event deposit energy very infrequently.
The energy deposition events from these low-LET are separated
in space so that on the average few ionizations or damaging
events occur in any one cell from a single x-or gamma ray. High-LET
radiation is more effective in producing cancer and other cellular
and molecular damage per unit of exposure or dose than low-LET
exposure. This may be related to the concentration of energy
from a single particle in a single cell and the ability of this
energy concentration to trigger bystander effects that influence
many more cells than are "hit" by the alpha particles.
NCRP National
Council on Radiation Protection and Measurements, 1990. The
Relative biological effectiveness of radiations of different
quality. NCRP Report No. 104. Issued December 15, 1990.
Bethesda, Maryland. National Council on Radiation Protection
and Measurements.
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What
is radiation dose?
There
are two formal definitions of dose. One is the energy deposited
at a point source and is useful in determining the dose distribution
during cancer therapy. The other is the amount of energy deposited
in a unit of tissue. This measurement of dose can be used to
represent the average dose to an organism, organ, tissue or
even a cell. There are many different types of radiation dose.
ICRP Publication
60. Recommendations of the International Commission on Radiological
Protection. Pergamon Press, Oxford, New York. (1990).
ICRU Publication
51. Quantities and units in radiation protection dosimetry.
1991.
ICRU 60.
Fundamental quantities and units for ionizing Radiation. 1998.
http://hps.org/publicinformation/ate/faqs/radiationdoses.html
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ARE
THERE HEALTH EFFECTS FROM RADIATION?
The Health Physics Society summarizes the answer to this complicated question nicely in their position statement.
"In accordance with current knowledge of radiation health risks, the Health Physics Society recommends against quantitative estimation of health risks below an individual dose of 5 rem in one year or a lifetime dose of 10 rem above that received from natural sources. Doses from natural background radiation in the United States average about 0.3 rem per year. A dose of 5 rem will be accumulated in the first 17 years of life and about 25 rem in a lifetime of 80 years. Estimation of health risk associated with radiation doses that are of similar magnitue as those received from natural sources should be stricly qualitative and encompass a range of hypothetical health outcomes, including the possibility of no adverse health effects at such low levels. There is substantial and convincing scientific evidence for health risks following high-dose exposures. However, below 5-10 rem (which includes occupational and environmentla exposures) risks of health effects are either too small to be observed or are nonexistent." (Health Physics News, Oct 2004)
Will
I get cancer if I am exposed to ionizing radiation?
The risk
for radiation exposure has been very widely studied with literally
billions of dollars invested to define and understand radiation
related health effects. The risk for the induction of cancer
by ionizing radiation is summarized in a very wide number of
reports from national and international committees. It is important to understand that radiation is a very good cell killer, as demonstrated in its wide use in cancer therapy. However, radiation is not a very strong carcinogen, especially at low doses. There is adequate data that suggest that for low doses of radiation that this is a conservative assumption since the body has many repair mechanisms that can handle the damage induced by low doses of radiation.This illustrates that at levels
of radiation of environmental concern the individual risk for
developing cancer is very small. Following exposures to low
levels of ionizing radiation it is not possible to detect a
change in cancer incidence. This is related to the many factors
that can produce cancer, the high background level of cancers
and the high and variable background levels of radiation exposure
in the population.
To calculate cancer risk from a specific dose::
(Dose in mrem) x (cancer risk of 0.04 cancers/Sv)* x (0.001 Sv/mSv) x (0.01 mSv/mrem) = Risk of radiation-induced cancer
* To calculate this conservative radiation cancer risk, the regulatory bodies use the recommendations of the NCRP 116 (Limit of Exposure to Ionizing Radiation) that calculates that cancer risk increases above the background rate of cancer by 4% per Sv of radiation dose.
NCRP National
Council on Radiation Protection and Measurements, 1980 Report
No. 64. Influence of dose and its distribution in time on dose-response
relationships for low-LET radiations. Issued April 1, 1980.
Bethesda, Maryland.
NCRP National
Council on Radiation Protection and Measurements, 1982). Critical
issues in setting radiation dose limits, In
Proceedings of the Seventeenth Annual Meeting of the National
Council of Radiation Protection and Measurements, Proceedings
No. 3, April 1, 1982.
NCRP National
Council on Radiation Protection and Measurements, 1987, Recommendations
on limits for exposure to ionizing radiation. NCRP Report
No. 91 (Bethesda, National Council on Radiation Protection and
Measurements).
NCRP National
Council on Radiation Protection and Measurements, Risk estimates
for radiation protection. NCRP Report No. 115. Issued
December 31, 1993. Bethesda, Maryland. National Council on Radiation
Protection and Measurements.
NCRP National
Council on Radiation Protection and Measurements, 1993, Limitation
of exposure to ionizing radiation. NCRP Report No.
116. National Council on Radiation Protection and Measurements,
Besthesda, Maryland.
http://hps.org/publicinformation/ate/q922.html
http://hps.org/publicinformation/ate/q487.html
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What
are the genetic effects of ionizing radiation?
The concern
for genetic effects of radiation has been present since the
first discovery of radiation and the observation that radiation
produced mutations in fruit flys. This observation triggered
extensive studies on radiation induced mutation. It is well
established that both internally deposited and external exposure
to ionizing radiation can cause mutations, chromosome aberrations
and transmitted genetic effects. The extent of these changes
is very easy to measure in specialized cell and tissue cultures.
In these cell culture experimental systems the number of mutations
increases as a linear function of radiation dose. Each unit
of dose causes an increase in mutation frequency. However, research
in mice demonstrated that there were changes in mutation frequency
as a function of both dose and dose rate and that the number
of mutations decreased as the radiation dose rate decreased.
In addition there are many steps and processes that a cell must
accurately go through before a sperm can fertilize and egg and
produce an offspring. Most damaged cells are eliminated by these
processes and do not result in offspring. Thus, the mutation
frequency in irradiated offspring is very low. This results
in the property of radiation that demonstrates that radiation
is a very good cell killer, so it is used in therapy, and it
is a weak mutagen and carcinogen. The risk for mutations has
been studied carefully in some very large animal studies. In
these studies male mice were given large doses of radiation
and the exposed animals produced hundreds of thousands of offspring.
With this large study it was possible to detect mutations in
a small number of animals. These data as well as in the follow-up
on the A-bomb survivors, where it has not been possible to detect
an increase frequency of mutations in the offspring of exposed
parents, support the conclusion that radiation is a weak mutagen.
Research is continuing on transgenerational effects of radiation
by mechanism other than direct DNA damage and mutation induction.
NCRP National
Council on Radiation Protection and Measurements, 1987. Genetic
effects from internally deposited radionuclides. NCRP Report
No. 89. National Council of Radiation Protection and Measurements,
Besthesda, Maryland.
NCRP 99,
William L. Russell mouse data, NAS 1980, BEIR III Report, Effects
on populations of low levels of ionizing radiation.
Baulch,
J.E., Raabe, O.G., Wiley, L.M., and Overstreet, J.W. (2002)
Germline drift in chimeric male mice possessing an F(2) component
with a parental F(0) radiation history. Mutagenesis
17(1):9-13.
http://hps.org/publicinformation/ate/q1916.html
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Will
exposure to an unborn child cause defects or death?
It is
well established that radiation of unborn children during well-defined
stages of fetal development, when the major organs are developing,
results in an increase in birth defects. During the early stages
of fetal development radiation exposure results in death of
cells that are critical to normal development. Loss of these
cell results in the death of the fetus. Thus, exposure during
early fetal development does not result in defects but causes
an increase in early spontaneous abortions. This is a defense
mechanism that the body has to eliminate fetuses that are not
developing normally. In the a-bomb survivors, the major defect
in the children born after the bomb was a decrease in head size
accompanied with mental retardation. These congenital birth
defects all seem to have a threshold dose at about 10 rads below
which there are no measurable effects.
BEIR III,
UNSCEAR (1986) United Nations Scientific Committee on the Effects
of Atomic Radiaiton: Sources and Effects of Ionizing Radiation
New York.
Brent,
R.I. and Ghorson, R.O. (1972) Radiation exposure during pregnancy.
Current Probl Radiol 2:1-48.
http://hps.org/publicinformation/ate/q61.html
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How
can cell and molecular research help in understanding the hazards
from radiation?
Recent
research has been able to take advantage of the many advances
in genomics, cell and molecular biology to detect changes in
cells exposed to low doses of ionizing radiation. The current
DOE Low Dose Research Program outlined on this site is one example
of an organization that is funding research to measure such
effects following radiation exposures of 10 cGy and less. Through
this research, it has been possible to make measurements that
change our thinking on how radiation interacts with matter to
result in biological damage. For example changes in cells that
are not "hit" by ionizing radiation have been observed
using a wide range of biological endpoints. These "bystander
effects" illustrate that contrary to conventional past
wisdom, a cell does not have to have energy directly deposited
in it to result in a biological change. This results in research
questions that are currently being addressed such as: Are these
bystander changes protective or a reflection of increased damage
and risk? The research has also demonstrated that the types
and numbers of gene activated by low doses of radiation are
different than those activated by high radiation doses. These
changes in gene activation seem to be able to modify the response
of cells to subsequent radiation exposure, termed the "adaptive
response". This adaptive response seems to be the manifestation
of a protective effect that may reduce risk at very low doses.
Cell and molecular research has also determine that cells may
lose their genetic control many cell generations following radiation
exposure. This is termed genomic instability and is thought
to be an essential step in radiation induced cancer. There is
a very active research effort being conducted to better understand
the impact of all these cell and molecular effects on the risk
for development of cancer.
Morgan,
W.F. (2003) Non-targeted and delayed effects of exposure to
ionizing radiation: I. Radiation-iInduced genomic instability
and bystander effects In vitro. Radiation Research
159:567-580.
Morgan,
W.F. (2003) Non-targeted and delayed effects of exposure to
ionizing radiation: II. Radiation-induced genomic instability
and bystander effects In vivo, Clastogenic factors
and transgenerational effects. Radiation Research 159:581-596.
Redpath,
J.L., Lu, Q., Lao, X., Molloi, S., and Elmore, E. (2003) Low
doses of diagnostic energy X-rays protect against neoplastic
transformation In vitro. Int. J. Radiation. Biol.
79(4):235-240.
NCRP National
Council on Radiation Protection and Measurements, 1993. Report
No. 117, "Research Needs for Radiation Protection",
Scientific Committee 83, Issued Nov 30, 1993, National Council
on Radiation Protection and Measurements, Bethesda, MD.
WSU Radiation
Research Web Site
http://hps.org/publicinformation/ate/q61.html
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What
is a "dirty bomb"?
The current
media use of the term "dirty bomb" to refer to a potential
terrorist activity where a conventional bomb is exploded to
disperse radioactive material, thereby contaminating a large
area. Although the dispersal of radioactive material and radiation
from the bomb will not be effective in killing people, it could
cause a huge public response and disrupt the economy and living
conditions in the area contaminated.
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Will
I die from the bomb?
As with
any bomb blast, if you are very close to the blast, you could
die from the explosion, falling objects or fire. There is very
little chance for you to die from the radiation exposure from
a "dirty bomb". Although a "dirty bomb"
is not a nuclear explosion, particles of radioactive material
will be produced, create a dust like material and result in
radioactive fallout. This radioactive fallout could potentially
be dispersed over large areas depending on the weather conditions.
This creates radioactive contamination. The question to be addressed
for any such event would be to determine the amount of radiation,
or dose to the exposed individuals exposed to these particles.
Once this is done it is easy to predict the health outcome based
on the very extensive past experience that is available from
nuclear weapons or nuclear accidents. The radiation exposure
and dose can be easily and rapidly measured and actions taken
to minimize the impact and insure that the radiation associated
with the bomb can not create a deadly hazard, except perhaps
in the immediate area of the bomb. If you are very close to
the bomb and are not killed by the blast there is the potential
for radiation sickness. If you are not close to the bomb you
will not receive a large radiation dose or get sick and can
expected to live for a normal number of years.
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How
do I know if I have been exposed?
Fortunately,
it is easy to determine if you have been contaminated by radioactive
fallout from to this type of bomb. Monitoring equipment, such
as a simple Geiger counter or other field instruments, can determine
if you have any of the radioactive fallout on or in your body.
If physical measurements suggest that you have been exposed,
there are predictable changes in your body that can be quickly
measured. The number of blood cells, the frequency of chromosome
aberrations in the blood cells and the amount of radioactive
material in your urine, are examples of biomarkers that can
quickly indicate if your exposure can be life threatening. If
you do not have early biological changes indicated by these
measurements the radiation exposure will not pose an immediate
threat to you.
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What
can I do to protect myself if I am close to a "dirty bomb"?
If you
are close to a "dirty bomb" when it goes off and know
that you have been exposed, the first thing to do is to quickly
get away from the bombed area. Radiation exposure decreases
rapidly as you get further away from the source. It is like
a campfire. If you are too close, you will get burned. However,
by putting a little distance between you and the source, the
damage and dose decrease very rapidly. The other factor is the
amount of time that you are being exposed. That is why it is
important to move quickly away from the site of a bomb. The
more distance you can put between you and the bomb the better.
Even a hundred yards can make a big difference in the level
of radiation exposure. [If you are exposed and contaminated
with radioactive materials, make sure that you change your clothes
and take a shower. Takin a shower will remove the radioactive
material from your skin.] It would be wise to have a radiation
test to determine if you have ingested or inhaled radioactive
materials. If the bomb contains radioactive iodine, health officials
will provide a dose of stable iodine to remove the iodine from
your body and prevent thyroid cancer in the future.
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How
long will the radiation stay in the area? When can I go back
to my home?
The length
of time the contamination is dangerous depends on the composition
of the fallout. Many radioactive materials decay quickly and
are safe in a matter of hours or days while other materials
may remain in the environment for hundreds of years. Public
officials with monitoring equipment can determine the type of
contamination, where it is located, and when the radiation has
returned to a level similar to normal background where it will
be safe to return to your home. If you live in an area that
is not safe, you will be evacuated. If this is the case, you
should not eat the food in your house or drink the water. You
will be given specific instructions as to how to clean things
safely when you return. If you are not evacuated, the sources
of food and water should not be contaminated, but will be monitored
to make sure that it is safe to use. Many of the types of radioactive
materials that are used in medical procedures and could be used
in such a bomb decay rather rapidly and are gone within a few
weeks. However, if materials with the longest half-lives were
used, decontamination methods developed at nuclear sites would
make it possible to return within a few years.
National
Council on Radiation Protection and Measurements. Oct. 2001
Management of terrorist events involving radioactive material,
NCRP Report No. 138, Bethesda, Maryland.
Medical Management of Radiological Casualties, Handbook, Military
Medical Operations, Armed Forces Radiobiology Research Institute,
Bethesda, Maryland 20889-5603, http://www.vnh.org/MedManRadCasu/
Disaster preparedness for radiology professionals, response
to radiological terrorism, American College of Radiology http://www.acr.org/departments/educ/disaster_prep/disaster_planning.html,
Contact Dr. Nancy Riese Daly, nancyd@astro.org
http://hps.org/publicinformation/ate/cat66.html
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What
is depleted Uranium?
Depleted
uranium is currently being used in war for making shielding
and projectiles. This use has raised questions about the potential
long-term health effects from the radiation exposure produced
by the uranium. Depleted uranium is mainly the non-fissionable
238 U with the fissionable 235U removed for making nuclear weapons
or nuclear fuel. 238U has a very long half-life, the length
of time that it takes for half of the radioactive material to
decay, of about 4,500,000,000 years and therefore results in
very few radiation disintegrations per unit of mass and time.
Depleted uranium thus, delivers very low radiation doses per
unit of mass. This is much less activity per unit of mass than
is found in many phosphate fertilizers, smoke detector or the
mantel from a camping lantern.
http://hps.org/publicinformation/asktheexperts.cfm
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Is
depleted uranium a serious radiation problem with potential
to produce cancer?
Since
238U is an alpha emitter, and alpha particles can be stopped
by a single layer of skin, it presents no radiation hazard from
external exposure. The concern is when large amounts of depleted
uranium are deposited in the body through wounds or inhalation.
Uranium is a heavy metal and as such is toxic, especially to
the kidneys. Depleted uranium has been shown to convert normal
cells in tissue culture to transformed cells. This may be a
function of its metal toxicity. On the other hand, we all have
uranium in our bodies from natural sources. Therefore the real
concern would be from addition of high levels of uranium to
our bodies. Such high levels would result from being "hit"
by fragments from a uranium bullet or being very close to where
a uranium bullet hit and ignited. This ignition can result in
the production of small particles of uranium oxide. The hazard
would be the inhalation of the uranium. Because of the high
mass of the uranium, the aerodynamic diameter of the particles
would tend to be large which makes it difficult for them to
remain in the air for a long enough time to create a major inhalation
hazard. These facts suggest that the radiation doses from Uranium
in the environment is of little concern. If there are "bystander
effects" produced by the alpha particles from the uranium
that result in many more of the cells in the tissue responding
than are "hit" by the alpha particles this could effect
the risk. To date it is not possible to determine if such bystander
effects would make the tissue more or less sensitive to the
toxicity of the uranium and if the risk could be increased or
decreased. Research needs to be further conducted to evaluate
the interaction between the know toxicity of the Uranium and
the potential for a very small radiation dose. Additional questions
and concerns can be addressed with the following references.
NCRP National
Council on Radiation Protection and Measurements, 1997. Deposition,
retention and dosimetry of inhaled radioactive substances. NCRP
Report No. 125. Issued February 14,1997. Bethesda, Maryland.
National Council on Radiation Protection and Measurements.
http://hps.org/publicinformation/asktheexperts.cfm
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HOW
DO WE DETECT THE PRESENCE OF RADIATION?
The development
of radiation detection equipment has been very successful. This
equipment is very very sensitive and can detect very low levels
of radiation, characterize the types of isotopes involved in
producing the radiation and estimate the radiation dose. This
equipment can detect both high- and low-LET radiation as well
as the type of radiation found during space travel. Such physical
dosimeters are critical in health protection. The web site for
the health physics society has a very good coverage on the types
of instruments used to detect the different types of radiation
and the sensitivity of each type of equipment.
http://hps.org/publicinformation/ate/faqs/radiationdetection.html
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What is 210Po ?
210Po (Polonium 210) is a naturally occurring radioactive alpha emitting radionuclide that is produced as a daughter product from the decay of Radon. It has a relatively short half-life (138 days). This means that every 138 days the amount of activity associated with 210Po will decrease by ½. This short half life requires very little mass of the Polonium to result in a very large number of radioactive decays over a short time producing a large radiation dose. 210Po is circulated through the blood and results in radiation of all the tissues in the body.
Were public health hazards associated with the 210Po contamination of the environment by Mr. Alexander Litvinenko?
Mr. Litvinenko was give a large amount of 210Po which resulted in a radiation-induced death. 210Po is secreted from the body in all the body fluids including exhaled water vapor, urine, feces and sweat. So everywhere Mr. Litvinenko went he left trace amounts of 210Po. Prior to his death, he was in many public places, which resulted in contamination of these locations with 210Po and potential contamination of large number of people. The Health Protection Agency in the UK characterized the extent of these contamination sites and calculated the amount of radiation dose that resulted in contamination of people at these sites. They divided the people tested into groups according to the calculated dose that they would receive from the measured level of 210Po in them. At the time of this review there were 601 people that were not significantly elevated above the background level of 210Po, 85 people that were calculated to receive 1 mSv, 35 between 1 and 6 mSv, and 17 with doses above 6 mSv. From these numbers and other extensive background information on the relationship between radiation dose and disease, it was concluded that there were no health concerns to any of the people with doses below 6 mSv, and that there was no cause for concern for illness in the short term for any of the people that were contaminated by 210Po from Mr. Litvinenko. It was also determined that the increase in long term risk form cancer development would be very small. Further results are being published in the open literature.
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