Influence of the uniformity of the slab phantom illumination on the calibration of personal dosemeters

Abstract

For the calibration of personal dosemeters in terms of H(p)(10), the ISO water slab phantom shall be used. The irradiation geometry must be chosen such that the field diameter at the phantom front surface is large enough to irradiate the phantom completely and, in addition, homogeneously. However, in practice it is not always possible to achieve this, especially if high dose rates are required and hence the irradiation must be performed at short distances. The subject of this investigation is to determine the influence of the beam diameter on the calibration result or, more correctly, on the quantity value of H(p)(10). Measurements were performed with a PTB-developed secondary standard chamber for H(p)(10) at several radiation qualities of the ISO narrow-spectrum series. The results show that a reduced beam diameter of only 250 mm decreases the quantity value of H(p)(10) by a maximum of 5 %. This can be considered by adding an additional standard uncertainty of a maximum of 5 % for the quantity value of H(p)(10).