Thermoluminescent dosimeter, TLD, is radiation dosimeter used for measuring ionizing radiation exposure by measuring the intensity of light emitted by a crystal inside the detector when the crystal is heated. It was invented by Professor Farrington Daniels of the University of Wisconsin-Madison in 1954.
It contains small chips of lithium fluoride, which absorb ionizing radiation energy. The radiation interacts with the crystal in the detector causing the electrons in the crystal's atoms to jump to higher energy states, where they get trapped in a metastable state but can be restored to their original ground state by heating. Whereby on heating, the electrons return to their ground state and light is emitted. The amount of light emitted is related to the dose of radiation absorbed by the TLD and to the radiation exposure dose of the individual.
They can be worn as rings or body badges, bearing the individual assignee’s name, date of the monitoring period and a unique identification number
A Thermoluminescent Dosimeter