Which dosimeter is read by heating the crystal to release stored energy?

• A. TLD
• B. OSL
• C. Film badge
• D. Pocket dosimeter

Answer: (A)

Thermoluminescent dosimetry relies on crystals that trap charge carriers when they’re exposed to ionizing radiation. The stored energy stays in the lattice until the crystal is heated. Heating supplies enough energy to release those trapped charges, and as they recombine, light is emitted. The amount of light generated is proportional to the absorbed dose, so by heating the crystal in a dedicated reader and measuring the light, you determine the exposure. This is why this type of dosimeter is read by heating the crystal to release the stored energy.

For context, optical stimulated luminescence uses light to release the energy, film badges darken on exposure, and pocket dosimeters use an ionization chamber read electrically. Common TLD materials include lithium fluoride crystals doped with elements like Mg and Ti, and the crystals are reset by annealing after readout.