A radiation dosimeter is a device that measures exposure to ionizing radiation. Dosimeters usually record a dose, which is the absorbed radiation energy measured in grays (Gy) or the equivalent dose measured in sieverts (Sv). A personal dosimeter is dosimeter, that is worn at the surface of the body by the person being monitored, and it records of the radiation dose received.
Characteristics of Dosimeters – Key Features
There are many types of dosimeters and detectors, and each type has limitations. Many factors influence the quality of a dosimeter’s results. Some key considerations when choosing a dosimeter include:
- Type of radiation. Each type of radiation interacts with matter in a different way. This consideration is crucial. For doses from neutrons, we cannot use a simple GM counter.
- Energy of radiation. A dosimeter’s response will vary depending on the energy of the radiation and the angle(s) between the source and the dosimeter’s detector.
- Fading. A dosimeter’s signal can be lost or fade over time. This can be caused by external factors such as temperature, light and humidity.
- Direct reading. Sometimes, it is of the highest importance, that the dosimeter can give a continuous readout of cumulative dose and current dose rate, and can warn the person wearing it when a specified dose rate or a cumulative dose is exceeded.
- Minimum measurable dose. The lowest dose that can be measured with a certain specified confidence level.
- Ruggedness and ease of wear. Dosimeters differ in their ability to withstand severe environmental conditions. Some heavy for a given purpose, some are smaller, lighter and more portable.
As can be seen, radiation dosimetry is very difficult, since no single dosimeter will have every one of these characteristics. Therefore, a dosimeter user must understand the environment where the instrument will be used. In most practical situations, dosimeters provide reasonable approximations to the personal dose equivalent, Hp(d), at least at the location of the dosimeter. It must be noted, the personal dose equivalent generally overestimates the effective dose. On the other hand, this procedure is valid only at low doses and under the assumption of a uniform whole-body exposure. For high personal doses approaching or exceeding the annual dose limit, or in strongly inhomogeneous radiation fields, however, this procedure might not be sufficient.
See also: The Radiation Dosimeters for Response and Recovery Market Survey Report. National Urban Security Technology Laboratory. SAVER-T-MSR-4. <available from: https://www.dhs.gov/sites/default/files/publications/Radiation-Dosimeters-Response-Recovery-MSR_0616-508_0.pdf>.
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