3.4 Personal Dosimetry and Monitoring
For individuals who work with or are potentially exposed to radiation, it is essential to measure and record their radiation dose to ensure safety and compliance with regulations. This process is known as dosimetry.
What is a Dosimeter?
A **dosimeter** is a small, portable device used to measure and record the cumulative radiation dose received by a person over a period of time. These are typically worn on the body, such as on a lab coat or in a pocket.
There are several types of dosimeters, each with a different working principle:
- Film Badges: Contain a small piece of photographic film that darkens in proportion to the radiation dose received. They are read on a regular basis to determine exposure.
- Thermoluminescent Dosimeters (TLDs): Use a crystalline material that, when exposed to radiation, traps electrons in a metastable state. When the crystal is heated, these electrons are released, emitting light that is proportional to the absorbed dose.
- Optically Stimulated Luminescence (OSL) Dosimeters: Similar to TLDs, these dosimeters use a crystal that, when stimulated by a laser, emits light proportional to the absorbed dose. This is a modern and highly accurate technology.
Active vs. Passive Monitoring
Dosimetry can be classified as either passive or active:
- Passive Dosimeters: These devices (e.g., film badges, TLDs, OSLs) record a cumulative dose and require a reader to determine the total exposure. They are typically worn for a period (e.g., a month or a quarter) and then sent to a lab for analysis.
- Active Dosimeters: Also known as electronic personal dosimeters (EPDs), these provide a real-time, instantaneous reading of the dose rate and accumulated dose. They are useful for situations where immediate feedback on radiation levels is needed.