Open Source Training Modules
Open Source Radiation Safety Training
Module 3: Biological Effects
This module provides information about the following topics:
Injury to living tissue results from the transfer of energy to atoms and molecules in the cellular structure. Ionizing radiation causes atoms and molecules to become ionized or excited. These excitations and ionizations can:
At higher levels, cell death results. At extremely high doses, cells cannot be replaced quickly enough, and tissues fail to function.
In general, the radiation sensitivity of a tissue is:
This also means that a developing embryo is most sensitive to radiation during the early stages of differentiation, and an embryo/fetus is more sensitive to radiation exposure in the first trimester than in later trimesters.
Radiation effects can be categorized by when they appear.
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High doses delivered to the whole body of healthy adults within short
periods of time can produce effects such as blood component changes, fatigue,
diarrhea, nausea and death. These effects will develop within hours, days
or weeks, depending on the size of the dose. The larger the dose, the
sooner a given effect will occur.
* The LD50/60 is that dose at which 50%of the exposed population will die within 60 days.
These acute effects apply only when the whole body is relatively uniformly irradiated. The effects can be significantly different when only portions of the body or an individual organ system are irradiated, such as might occur during the use of radiation for medical treatment. For example, a dose of 500 rem delivered uniformly to the whole body may cause death while a dose of 500 rem delivered to the skin will only cause hair loss and skin reddening.
Using the linear no-threshold risk model, the 1990 BEIR* V report provided the following estimate:
Another way of stating this risk:
One way of considering the level of a risk
is to look at the number of "days lost" out of a population due to
early death from a given cause, then distributing those days lost
population to get an "average life expectancy lost" due to that cause.
The following table provides an estimate of life expectancy lost
to several causes:
You can also look at risk by considering the Relative Risk of a 1
in a million chance of death from activities common to our society:
(Adapted from DOE Radiation Worker Training based on work by B.L. Cohen, Sc.D.)
There is no direct evidence of radiation-induced genetic effects in humans, even at high doses. Various analyses indicate that the rate of genetic disorders produced in humans is expected to be extremely low, on the order of a few disorders per million live born per rem of parental exposure.
Rapidly proliferating and differentiating tissues are most sensitive to radiation damage. Consequently, radiation exposure can produce developmental problems, particularly in the developing brain, when an embryo/fetus is exposed prenatally.
The developmental conditions most commonly associated with prenatal radiation exposure include low birth weight, microcephaly, mental retardation, and other neurological problems. These effects are related to the developmental stage at which the exposure occurs. The threshold dose for developmental effects is approximately 10 rems.
The evidence that the developing embryo/fetus is more sensitive to radiation-induced cancer is inconclusive. But it is prudent to assume that there is some increased sensitivity.
This is the end of the Biological Effects Module, which is the third of the four Radiation Basics modules. The next module is the Regulations Module.
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