For personal dosimetry, the standard procedure is to wear an individual whole body dosemeter on the chest. Depending on the specific requirements, this can be supplemented with a wrist, finger, eye lens or lead apron dosemeter. Approximately 7,000 Belgian employees are currently wearing dosemeters supplied by the Belgian Nuclear Research Centre.
The various types of dosemeters all consist of a holder in which the dosemeter itself is inserted. Inside the dosemeter are the detectors that are sensitive to both beta and gamma rays.
The radiation dose of professionally exposed employees is usually monitored on a monthly basis, but the exchange of the dosemeter every three months is also possible. The natural background radiation is subtracted from the result.
Whole body dosemeter
A body TLD consists of a holder containing three detectors. This dosemeter is sensitive to beta, X and gamma rays. Due the various detector filters, one detector measures the depth dose Hp(10), and the other the surface dose Hp(0.07). A third detector in the dosemeter serves as a back-up.
Facts & Figures: SCK•CEN body dosemeter
- Minimum detectable dose: 50 µSv
- Measurement range: 50 µSv to 20 Sv
- Reproducibility: 20 %
- X-rays and gamma energy range: 12 keV to 6 MeV
- Beta energy range: 500 keV to 3 MeV (expressed in Emax)
- Small and light
- PVC disk: 4.2 cm diameter
- 10 mm thickness
- 15 g
If radioactive products are manipulated by hand, it may be necessary to also wear a finger and/or wrist dosemeter in addition to a body dosemeter on the chest. Like a body dosemeter, a wrist dosemeter contains three detectors. Ring dosemeters consist of a plastic ring with one single thermoluminescent detector.
When a ring or wrist dosemeter is worn, it is important that the detector is directed as much as possible towards the source of radioactivity; usually this means facing the inside of the hand or the wrist. Examples of personnel who wear finger dosemeters are operators working in a nuclear medical department or people working in glove boxes.
Eye lens dosimetry
The existing dose limits for the eye lens were recently made stricter. This means that it is recommended to wear an eye lens dosemeter for certain applications, for example for cardiologists who are working in an interventional cardiology department. Please contact the SCK•CEN dosimetry expert group for information in this field.
Lead apron dosimetry
When a lead apron is used for radiation protection, the question arises as to whether the dosemeter should be worn above or underneath the lead apron. In this case, SCK•CEN suggests double dosimetry. The person then wears a body dosemeter above as well as underneath the lead apron. For the read-out and reporting of the exposure dose, the dosimetry laboratory uses an algorithm that takes the results of both dosemeters into account.