603Chapter 11
Dosimetry and Radiation Protection
The extensive use of radiation in many fields has prompted the development of
the field of radiation dosimetry. Originally the emphasis was on determining the
integrated dose received by a person working in a radiation intensive environment
with the intention to limit the exposure for personal safety. However, the discovery
that radiation may also affect materials to the point that they become unusable, has
stretched the applicability of this field to industrial and research purposes. We have
already seen in the chapter on semiconductor detectors that radiation damage poses
a major problem specially in high radiation fields. This has lead the researchers,
such as physicists working at particle accelerators, to establish continuous dosimetry
programs for their detectors. Other areas where dosimetry plays a central role are
medical diagnostics and radiation therapy.
Most of the detectors used for dosimetry are based on the designs we have already
discussed in earlier chapters. In this chapter we will look at the most commonly
used dosimetry techniques.11.1ImportanceofDosimetry
It is a universally accepted fact that radiation causes damage, which can range from
a subtle cell mutation in a living organism to the bulk damage in a silicon detector.
The type of damage depends mainly on the type and energy of radiation and the
type of material. This damaging mechanism of radiation is sometimes exploited for
the benefit of mankind. An obvious example is the radiation therapy of cancer,
where cancer cells are targeted and destroyed by radiation.
Unfortunately the damage caused by radiation can not always be easily quanti-
fied. Some types of cell mutations caused by radiation take years to develop into
detectable cancer. The same is true for electronic components that are in a hos-
tile radiation field. The damage is so slow that often it is hard to notice the small
degradation in performance. The question is, how do we then find out if a particular
individual or equipment has received a high enough dose. The answer lies in the
statistics. There have been extensive studies to determine thesaferadiation levels
for individuals, radiation workers, and equipments using statistical inferences of the
damage data collected over a long period of time. Based on these studies, standards
have been set for maximum allowable dose to humans. For materials, in most of
the cases, such as silicon detectors in a particle accelerator, the issue is operational
degradation and not safety and therefore no universally accepted standards exist.