Which crystal is used in thermoluminescent dosimeters?

• A. Lithium Fluoride
• B. Calcium Fluoride
• C. Sodium Iodide
• D. Strontium Tungstate

Answer: (A)

Thermoluminescent dosimetry relies on trapping charge carriers in a crystal after exposure to radiation and then releasing that energy as light when the crystal is heated. The crystal material determines sensitivity, dose-readout linearity, and how closely the material mimics tissue. Lithium fluoride is the crystal of choice because it is tissue-equivalent in its interaction with radiation and produces a well-characterized, stable light signal when heated. When doped (as LiF:Mg,Ti, for example), radiation creates traps that store energy and, upon heating, release it as photons in a glow proportional to the absorbed dose. This combination of tissue equivalence, reliable glow characteristics, and predictable readout makes LiF the standard TLD material.

Calcium fluoride can be used in some dosimetry contexts but is less common for thermoluminescent dosimeters. Sodium iodide is a scintillator used in fast light production for gamma detectors, not a thermoluminescent material. Strontium tungstate is a luminescent phosphor used in other imaging or display applications rather than the typical TLD crystal.