RADIATION PROTECTION - ILEA

2 | Energy and Injury 19
2 Energy and Injury
The production of injury to living matter by ionizing radiation is the result
of the transfer of large amounts of energy indiscriminately to individual
molecules in the region through which the radiation passes. These
large energy transfers cause the ejection of electrons from atoms and initiate
a variety of chemical and physical effects, the most critical being
those which damage the DNA molecules (Little, 1993). The cell has enzymatic
processes for repairing certain types of damage, but if it is unable
to repair the damage, the cell may die or be mutated into a malignant
cancer cell. Thus the imparting of energy by ionizing radiation to living
matter may be characterized as a potentially harmful process, and the
greater the energy imparted, the greater is the initial damage produced. Because
the transfer of energy plays the key role in the production of injury
by ionizing radiation, all measurements and calculations to evaluate the
hazard from ionizing particles have as their initial object the determination
of the energy imparted by the ionizing particles to the region of
concern.
The region affected by the action of a single ionizing particle or ray is
small, the damage caused to the person is insignificant, and the risk of induction
of any serious delayed effects, such as malignancy, is extremely
low. The damage produced by successive particles accumulates, however.
Although the effect may be accompanied by some repair for certain types
of particles, if enough energy is imparted, the consequences can become
serious. To prevent these consequences from developing, limits are set on
radiation exposure from ionizing particles. The limits are derived from
epidemiologic and laboratory data on the relationship between the energy
imparted to the body and injury produced. In essence, they specify the
maximum energy allowed to be imparted by ionizing particles to critical
regions in the body.
The effects produced by ionizing particles depend not only on the
amount of energy imparted to the body but also on the location and extent
of the region of the body exposed and the time interval over which the energy
is imparted. These and other factors must be taken into account in
specifying maximum exposure levels.
While the human body can sense and take measures to protect itself
from injury from most physically destructive agents—heat, noise, missiles,
and so on—it cannot sense exposure to radiation except at levels that are
invariably lethal. Thus we see how important it is to understand how to
anticipate radiation problems through calculations and analyses and how
to use radiation instruments to monitor the emissions from radiation
sources.