Thermoluminescent Dosimeter
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A thermoluminescent dosimeter, or TLD, is a small device used to measure radiation exposure by measuring the amount of visible light emitted from a crystal in the detector when the crystal is heated. The amount of light emitted is dependent upon the radiation exposure.
There are two main types of TLDs. Both consist of a small crystal, either calcium fluoride or lithium fluoride. The former is used to record gamma exposure, the latter for gamma and neutron exposure. As the radiation interacts with the crystal it causes electrons in the crystal's atoms to jump to a higher energy state, where they stay trapped due to impurities (usually manganese) in the crystal, until heated. Heating the crystal causes the electrons to drop back to their normal ground state, releasing a photon of specific frequency.
See also
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