c. Another long-term effect is leukemia, or cancer of the white blood cells. The
evidence, as with cancer, is statistical, but there is a higher incidence of leukemia
among those who have been exposed to excessive amounts of radiation than in the
d. By a similar statistical reasoning process, some studies have shown that
radiation exposure decreases the life span of the irradiated population. By exposing
large numbers of experimental animals to low levels of radiation over their entire life
span, it has been shown that life span-shortening does occur and is probably due to
e. Finally, one of the most significant long-term effects is the possibility of
genetic damage or mutation. A mutation is a hereditary change that can be passed
from generation to generation. Most mutations are harmful rather than beneficial; it is
therefore not desirable to increase the mutation rate.
(1) In 1928, it was shown that radiation exposure increased the genetic
mutation rate in fruit flies. Since that time, this mutation effect has been observed in
many animals, but data in humans are lacking due to the complexity of human genetics.
(2) The important point to remember in considering the relationship between
radiation and genetic effects is that radiation does not create new mutations, but rather
increases the rate of mutations already present in the population. Most mutations are
recessive; that is, both parents must possess mutant germ (reproductive) cells before
the offspring will exhibit the mutant characteristic. For this reason, several generations
may pass before the mutation will actually be seen in the population.
f. It is not known whether the effect at low exposures may be determined by
assuming that there is a linear relationship between dose and effect, where even very
small doses will produce some effect, or whether a threshold dose exists below which
no effect will occur. Evidence indicates that cancer would fit the nonthreshold model,
while other effects, such as cataracts, are threshold in nature. For radiation protection
purposes, the linear, nonthreshold approach is used and all occupational exposures are
maintained as low as reasonably achievable (ALARA).
Section V. RADIATION DETECTION INSTRUMENTS
1-19. DETECTOR FUNDAMENTALS
a. Nuclear radiation cannot be detected by any of the human senses; therefore,
detection instruments must be used to measure radiation intensity. If such instruments
were not available, it would be possible for personnel to be exposed to sizable, even
lethal, doses of radiation without warning at the time of exposure. Only with the