Identification of static and dynamic exposure of standard dosimetric badge with thermoluminescent detectors

Full text: There are three main methods used in individual monitoring: photographic, where exposure is estimated by film density; thermoluminescent (TL), where dose is measured through light emitted by the thermoluminescent detector (TLD) and optical stimulated luminescence (OSL), where the light emitted from detectors during light stimulation is counted with photomultiplier. Up to now the one undeniable advantage of films was the possibility of determining whether the dosemeter was exposed statically, e.g. by leaving it accidentally or purposely in the radiation field, or exposed dynamically, while being worn by a worker moving through a radiation field. Static exposure will show a sharp image of the filter edge, while a blurred image indicates dynamic conditions of exposure. This effect enables the service to distinguish between cases of actual exposure of a radiation worker wearing a badge and exposure of the dosemeter only. The problem with distinguishing static and dynamic exposure using OSL has been already solved. The main objective of this work is to develop a method for identifying static exposure of standard TL detectors at the dose level of interest for radiation protection. For this purpose a new TL reader with CCD camera has been developed. The reader enables not only the measurement of the total light emitted (like any standard TL reader with a photomultiplier), but also displays a two-dimensional signal map. In our tests, standard MCP-N (LiF:Mg, Cu, P) TL pellets of diameter 4.5 mm and thickness 0.9 mm were used. A Rados TL personal badges with special filters made of copper, led and aluminium containing 1 mm wholes were prepared and tested in x-ray exposure-simulated conditions. TL dosemeters with detectors were exposed in the x-rays beam statically facing with filters, while for dynamic conditions were rotated perpendicularly. The energy of x-ray beam varied from 28 keV up to 250 keV. Detectors were evaluated in the CCD camera reader and 2D images were collected. Calculations based on the CCD images obtained indicate the possibility of distinguishing between static and dynamic exposure at the dose level of 20 mSv for X-rays with energy below 125 keV. (author)