Читать книгу Patty's Industrial Hygiene, Physical and Biological Agents - Группа авторов - Страница 54

The ICRP recommends monitoring individual workers whose annual external doses are likely to exceed 1 mSv (100 mrem), and those workers whose annual doses are likely to exceed 5 mSv (500 mrem) “should certainly be monitored.” The USNRC requires personal monitoring if a worker's annual external dose is likely to exceed 10% of the dose limit. Despite the legal requirement for monitoring only those workers whose dose is likely to exceed 10% of the limit, it is reasonable to monitor all radiation workers in case a question should arise in the future about the possible relationship between the worker's ill health and his occupational radiation dose. In addition to monitoring for legal reasons, knowledge of personal doses and dose distribution can contribute to the control of operating procedures and to the design of facilities. Personal monitoring for external radiation is accomplished by personal dosimeters that are worn by individual workers. These dosimeters are discussed in the following sections, and a summary is provided in Table 5.

TABLE 4 Detector selection for particle counting and contamination control.

Detector type	Application	Ability to detect α	β	γ
G–M	Surface scanning, measurement of smear samples	Good (>4 MeV)	Good (>70 keV)	Poor
ZnS(Ag)	Surface scanning, measurement of smear samples	Good (>4 MeV)	Poor	Poor
NaI(Tl)	Surface scanning, measurement of smear samples	Poor	Poor	Good

TABLE 5 Advantages and disadvantages of common dosimeters.

Dosimeter	Advantages	Disadvantages
Film	Permanent record, tissue equivalent	Requires wet chemical developing
OSL	Can be reread, tissue equivalent, low detection threshold, high detection possible	Insensitive to neutrons (neutron sensitive OSL dosimeters are in development)
TLD	Variety of sensitivities, tissue equivalent	Cannot be reread
Electronic dosimeters	Can be read at any time by user, self‐contained alarm. Can be used as dosimetry of record	Directional, expensive, can be energy dependent, usually sensitive only to gamma rays
Pocket dosimeters	Can be read at any time by user	Easily fail if dropped, not suitable for dosimetry of record