Thermoluminescent Dosimeter

A thermoluminescent dosimeter, or TLD, is a type of dosimeterits cool stuff. A TLD measures ionizing 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 higher energy states, where they stay trapped due to impurities (usually manganese or magnesium) in the crystal, until heated. Heating the crystal causes the electrons to drop back to their ground state, releasing a photon of energy equal to the energy difference between the trap state and the ground state. The electrons can also drop back to ground state after a long period of time; this effect is called fading and is dependent on the incident radiation energy and intrinsic properties of the TLD material.

It can be used both for environmental monitoring and for staff personnel in facilities involving radiation exposure, among other applications.