660 Chapter 11. Dosimetry and Radiation Protection
11.6.BEffectsandSymptomsofExposure...............
In the preceding sections we discussed how radiation affects living organisms and
also looked at its effects on human body. In general, the effects on humans can be
divided into two categories: somatic effects and genetic effects.
B.1 SomaticEffectsofRadiation
The somatic effects are the ones that appear in the person that is exposed to ra-
diation. As discussed earlier, the effect can become obvious immediately after the
exposure or can take a long time to cause noticeable changes. For example, high
dose to skin can cause immediate reddening of the exposed area. Such a prompt
exposure is typical of high levels of radiation delivered in a short period of time.
On the other hand, most cancers take many years to develop and cause symptoms
that could lead to diagnosis. Such delayed effects are caused by cell mutations and
subsequent uncontrolled reproduction. Whether the effect is prompt or delayed, if
it appears in the person being exposed, it is called a somatic effect.
B.2 GeneticEffectsofRadiation..................
We saw earlier that if the chromosome of a cell gets permanently damaged, it can
lead to genetic changes. If the exposed cell is related to reproduction, the damage to
its DNA can lead to developmental problems in the offspring of the person. Such cell
changes are generally termed asgermline mutationsand do not affect the exposed
person. The hazards associated with germline mutations range from premature
death and miscarriage to cancer in later life.
A number of studies have been performed to determine the probability of damage
due to germline mutations. Since it is difficult to determine whether a germline
mutation in an individual has occurred or not, these studies have largely been based
on finding the correlation of dose received by radiation workers and the genetic
disorders in their children. Fortunately up until now, no conclusive evidence of strong
correlation between the exposure and childbirth defects has been found. However
a few studies have indicated that the occurrence of leukemia on the children whose
fathers received occupational exposures was about 2 to 2.5 times higher than in
general population. Unfortunately these studies have suffered from low statistics,
that is, the number of individuals available for analysis were fairly small. Because of
this, many researchers do not regard this inference as conclusive evidence of leukemia
occurrence in children. It should, however, be mentioned that the type of exposure
to father has also been found to be important in this regard. The internal exposure
to radionuclides is considered as a high risk cause of childhood cancer as opposed to
whole body exposure.
11.6.CExposureLimits
We just saw that radiation can not only induce acute damage but also cause subtle
cell mutations. Unfortunately the effects of cell mutations become obvious only after
an extended period of time. For example, it has been observed that people, who are
continuously exposed to low level of radiation, have a high probability of developing
some kind of cancer. The question then arises as to what are the safe limits of dose