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A Thermoluminescent Dosimeter (TLD) badge is a personal radiation monitoring device worn by radiation workers (radiologists, radiotherapists, nuclear medicine staff, technicians, etc.) to measure and record the amount of ionizing radiation exposure over time.

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Atomic energy regulatory board (AERB) infographic

TLD.pdf

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It uses thermoluminescent crystals (commonly lithium fluoride – LiF, calcium sulfate doped with dysprosium, or calcium fluoride doped with manganese) that store energy when exposed to radiation and release it as light upon heating. The emitted light is proportional to the absorbed radiation dose.

Principle

• Ionizing radiation excites electrons in the crystal lattice of TLD material.
• Electrons get trapped in defects (impurity sites) in the crystal structure.
• When the crystal is heated in a TLD reader, trapped electrons return to ground state, emitting photons.
• The intensity of emitted light is proportional to radiation dose received.

Structure of a TLD Badge

1. Plastic badge holder – contains filters of different materials (Cu, Al, plastic) to differentiate between radiation types and energies.
2. TLD cassette – houses the thermoluminescent discs (usually 3 chips/discs).
3. Identification card – carries wearer details, number, and monitoring period.

Types of TLD Materials

Advantages