11.6. Biological Effects of Radiation 659
fluid build-up in the brain ultimately leading to death. The exposure can cause
severe shock and even coma. At the minimum, the exposed person can suffer
from confusion, speech difficulty, and coordination loss.Dose> 25 Gy:This much exposure can cause epidermal and deep skin necro-
sis.Dose> 10 Gy:A dose higher than 10Gycan cause damage to the lining of
intestines and stomach leading to gastrointestinal complications. The exposed
person initially suffers from nausea, vomiting, and diarrhea, which can lead to
dehydration. Severe effects include formation of ulcers and inability to digest
food. Other probable damage is the atrophy of the skin with complications.Dose> 5 Gy:It can lead to visual impairment and cataract.Dose>3.5Gy: This much dose can lead to permanent sterilization if the
reproductive organs are directly exposed.Dose> 2 Gy:A dose higher than 2Gycan cause hair loss and erythema or
reddening of the skin.Dose> 1 Gy: A number of organs such as bone marrow, spleen, and lym-
phatic tissues are highly susceptible to radiation damage and therefore even
the moderately high dose of 1Gycan cause severe damage to their cells. The
damage can cause internal bleeding leading to bacterial infections and possibly
death.Dose> 500 mGy:Benign tumor growths in thyroid glands are common after
receiving a dose higher than 500mGy. Other effects include damage to bone
marrow and opacities in the ocular lens.A.2 ChronicExposure
In the preceding section we saw that an acute dose can bring serious health hazards.
The same is true for a low level dose received in a long period of time. Such an
exposure is said to be chronic. The distinguishing aspect of the chronic exposure is
that it is very difficult to assign deterministic effects to it.
The effects of chronic exposure become obvious after a long time, of the order
of several years. For example, some kinds of cancers can take up to 25 years to
produce symptoms and get diagnosed. At that time it becomes difficult to determine
whether the cause of the cancer was radiation exposure or something else. Such a
longincubationperiod of the disease makes it difficult to determine safe levels of dose
for workers and general population. One way to derive such statistical inferences
is to study the disease rates in populations that are exposed to different levels of
radiation. Such studies have been undertaken by many researchers but the results
have not been found to be statistically significant to make predictions. Due to this
difficulty the so calledsafelevels have been devised by extrapolating acute doses
with known deterministic effects.