A procedure for the distinction between static and dynamic radiation exposures of personal radiation badges using pulsed optically stimulated luminescence

摘要

A method is described for the distinction between the normal, "dynamic" radiation exposure of a personal radiation dosimetry badge during normal wear of the badge, and an abnormal, or "static" exposure of the badge in a fixed position relative to a radiation source. An example of a static exposure would be the intentional (unauthorized), or accidental, exposure of the badge to a radiation source when the badge is not being worn by a person. Other abnormal exposure conditions of interest include when the badge is accidentally partially shielded by (say) coins or other heavy material during incorrect wear of the badge (e.g. in a pocket) such that the usual reading of the badge may reveal a lower-than-expected absorbed dose reading. This paper describes the use of Pulsed Optically Stimulated Luminescence (POSL) as a dosimetric readout mode and the application of this technique to "imaging" of the dose distribution across the face of a large area Al2O3:C dosimeter. The technique relies upon the use of a radiation filter with a periodic array of holes, or other weakly absorbing regions, such that the Al2O3:C is exposed in a pattern which follows the pattern of the filtration. Subsequent illumination of the Al2O3:C using a defocused laser beam reveals a pattern of luminescence emission corresponding to the pattern of the absorbed dose. During static exposure, the absorbed radiation pattern is sharp and clear, whereas during dynamic exposure the absorbed radiation pattern is diffuse. Image processing of the collected POSL emission pattern using a Discrete Fourier Transform produces a spatial frequency spectrum of the collected image from which a factor is calculated which indicates the probability of static versus dynamic exposure. Furthermore, the POSL image obtained (vis-a-vis the absorbed radiation dose pattern) can also reveal accidental shielding. The image collection procedure, the image processing algorithms, and two different methods to determine the probability factor are described. Application of the technique to several exposure conditions is illustrated. (C) 2000 Elsevier Science Ltd. All rights reserved. [References: 1]