Читать книгу Patty's Industrial Hygiene, Physical and Biological Agents - Группа авторов - Страница 56

Several different crystals emit light when they are heated after having been exposed to ionizing radiation. The intensity of the emitted light is proportional to the amount of energy, and hence to the radiation dose, absorbed by the crystal. This effect is called thermoluminescence, and dosimeters based on this principle are called thermoluminescent dosimeters (TLDs). Absorption of energy from the radiation excites the atoms in the crystal; the excitation energy remains trapped in the crystal until the crystal is heated and the trapped excitation energy is released as light. For personal monitoring, a small piece of thermoluminescent material is placed into a small holder that is worn by the worker being monitored. After being worn for the prescribed period of time, the TLD material is heated and the resulting luminescence is measured with a photomultiplier tube. The instrument is calibrated by measuring the intensity of light from TLDs that had been exposed to known doses of radiation. TLDs used to monitor radiation workers can measure doses down to about 1 mrem. Other thermoluminescent materials that are available for use in environmental monitoring are sensitive to doses as low as 0.01 mrem.