Personal Dosimeter: TLD

A Thermoluminescent Dosimeter (TLD) is a personal dosimeter used to monitor occupational exposure to ionizing radiation.

Construction

A typical TLD badge contains:

• One or more thermoluminescent detector elements, such as lithium fluoride (LiF).
• Filters made from materials such as plastic, aluminium or copper to help distinguish radiation energy/type.
• A holder or badge containing the detector.
• Identification and protective casing.

Working Principle

When ionizing radiation strikes the TLD material, electrons are raised to higher-energy states and become trapped at defect sites in the crystal lattice.

During readout:

1. The TLD element is heated in a controlled reader.
2. Trapped electrons return to lower-energy states.
3. Light is emitted during this process.
4. A photodetector measures the emitted light.
5. The light output is related to the absorbed radiation dose after calibration.

Radiation Exposure
       ↓
TLD Crystal
       ↓
Energy stored in traps
       ↓
Controlled Heating
       ↓
Thermoluminescence
       ↓
Photodetector
       ↓
Dose Calculation

Advantages

• Small and lightweight.
• Good sensitivity.
• Passive and requires no battery during exposure.
• Can measure accumulated occupational dose.
• Available in reusable formats after readout.

Limitations

The TLD does not provide an immediate real-time reading during exposure. It requires a reader for dose evaluation and must be properly calibrated.

Applications

TLDs are worn by radiographers, radiologists, nuclear-medicine workers and other personnel who may be occupationally exposed to ionizing radiation.

Conclusion

A TLD records radiation exposure by storing energy in crystal traps and releasing it as light during controlled heating; the emitted light is used to estimate personal dose.