PERSONAL DOSIMETERS A thermoluminescent dosimeter (TLD), or film badge, is used to provide permanent records of cumulative-dose received. Most of these devices measure beta, x, and gamma radiation. The dose is recorded in rem or sievert. Dose measurements are not immediately available to the wearer because both of these devices require processing. Self-reading pocket dosimeters may be used in addition to TLDs. These devices provide immediate estimates of cumulative exposure of x and gamma radiation. Most pocket dosimeters can be directly read when held up to a light source. Estimates are typically recorded in milliroentgen (mR).
RADIATION SURVEY METERS Ion chambers are common types of survey meters for recording exposure rates of x and gamma radiation. Some types of ion chambers are equipped to also detect beta radiation with a Mylar (Dupont) window beneath a removable shield. These instruments are usually calibrated in mR/h. Geiger-Müeller (GM) instruments are commonly used to perform surveys for external contamination. These instruments detect lower exposure rates of x and gamma radiation, as well as beta radiation. With special instrument probes, alpha radiation can also be detected. The units recorded are typically counts per minute (cpm). For comparison, 2500 cpm is approximately equal to 1 mR/h.
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