What is a thermoluminescent dosimeter (TLD)?

• A. An active dosimeter with real-time readout.
• B. A passive dosimeter that records dose via trapped electrons released as light when heated.
• C. A gamma-ray spectrometer.
• D. A device used to measure air kerma.

Answer: (B)

A thermoluminescent dosimeter is a passive device that records radiation dose by trapping charge carriers in a crystal lattice after exposure. When the dosimeter is later heated, the trapped electrons are released and recombine with holes, emitting light in the process. The light output is proportional to the absorbed dose, and a reader measures this light to determine how much radiation was received. Because it relies on heating to read out the signal, it provides an integrated dose over the exposure period rather than real-time measurements. It is not an active device with continuous readout, nor a gamma-ray spectrometer, nor a device that directly measures air kerma.