Thermoluminescent dosimeter

A thermoluminescent dosimeter, or TLD, is a type of radiation dosimeter, consisting of a piece of a thermoluminescent crystalline material inside a radiolucent package.

When heated, the crystal releases the trapped energy in the form of visible light, the intensity of which is proportional to the intensity of the ionizing radiation to which the crystal was exposed.

It was invented in 1954 by Professor Farrington Daniels of the University of Wisconsin-Madison.

The former is used to record gamma exposure, the latter for gamma and neutron exposure (indirectly, using the Li-6 (n,alpha) nuclear reaction; for this reason, LiF dosimeters may be enriched in lithium-6 to enhance this effect or enriched in lithium-7 to reduce it).

Other types include beryllium oxide,[3] and calcium sulfate doped with thulium.