Читать книгу Patty's Industrial Hygiene, Physical and Biological Agents - Группа авторов - Страница 59

Pocket dosimeters are of the size and shape of a fountain pen. Two different types of pocket dosimeters are typically used. One of these, a condenser type, is simply a capacitor that is fully charged before exposure to radiation. Ionization produced by the radiation neutralizes the charge on the capacitor, and thus reduces the voltage across the capacitor. This reduction in voltage is directly proportional to the radiation dose. The instrument is charged before exposure, and the dose read after exposure, in a charger–reader. Commercially available condenser‐type dosimeters measure integrated X‐ray or gamma ray doses up to 200 mrem, with an accuracy of about ±15% for quantum energies of about 50 keV to 2 MeV.

The second type of pocket dosimeter is direct reading (and therefore is often called an “SRD,” a self‐reading dosimeter). It operates on the principle of a gold‐leaf electroscope. A gold‐plated quartz fiber is displaced electrically by charging it to a potential of about 200 V at which time the instrument reads zero. An image of the fiber is focused on a scale by an optical system within the SRD and is viewed through a lens at the other end of the instrument. Exposure to radiation discharges the fiber, thus allowing it to move back toward its uncharged position. The amount of discharge, and therefore the position of the fiber, is directly proportional to the radiation dose. These dosimeters read up to 200 mrem of X‐ray or gamma radiation with an accuracy of ±15% across an energy span of about 50 keV to 2 MeV.