Which substance is used in dosimeters to measure exposure?

• A. Lithium fluoride
• B. Potassium iodide
• C. Aluminum oxide
• D. Sodium fluoride

Answer: (A)

Lithium fluoride is used in dosimeters because it behaves like tissue when it absorbs ionizing radiation and stores that energy until it is read out. In thermoluminescent dosimeters, exposure excites traps in the LiF crystal. When the material is later heated, those trapped electrons release the stored energy as light, and the amount of light emitted is proportional to the absorbed dose. This makes LiF-based dosimeters reliable, sensitive across a broad range of energies, and easy to interpret for measuring exposure.

Potassium iodide isn’t a dosimeter material; it’s taken to protect the thyroid from radioactive iodine. Aluminum oxide is used in a different readout method, optically stimulated luminescence, where light stimulates release of stored energy rather than heat. Sodium fluoride can be used in some dosimeter formulations, but lithium fluoride’s tissue-like properties and well-understood response make it the preferred material for standard dosimetry.