Biomedical Engineering Reference
In-Depth Information
15
External Radiation Protection
We now describe procedures for limiting the dose received from radiation sources
outside the human body. In the next chapter we discuss protection from radionu-
clides that can enter the body.
15.1
Distance, Time, and Shielding
In principle, one's dose in the vicinity of an external radiation source can be re-
duced by increasing the distance from the source, by minimizing the time of expo-
sure, and by the use of shielding. Distance is often employed simply and effectively.
For example, tongs are used to handle radioactive sources in order to minimize
the dose to the hands as well as the rest of the body. Limiting the duration of an
exposure significantly is not always feasible, because a certain amount of time is
usually required to perform a given task. Sometimes, though, practice runs before-
hand without the source can reduce exposure times when an actual job is carried
out.
While distance and time factors can be employed advantageously in external ra-
diation protection, shielding provides a more reliable way of limiting personnel
exposure by limiting the dose rate. In principle, shielding alone can be used to
reduce dose rates to desired levels. In practice, however, the amount of shielding
employed will depend on a balancing of practical necessities such as cost and the
benefit expected.
In this chapter we describe methods for determining appropriate shielding for
the most common kinds of external radiation: gamma rays, X rays from diagnos-
tic and therapeutic machines, beta rays with accompanying bremsstrahlung, and
neutrons.
