Comparative Measurements of 147Pm Beta Particle Depth-Dose Distributions by Using an Extrapolation Chamber, Radiochromic Dye Film and 7LiF Ultrathin Thermoluminescence Dosemeters

Abstract

Comparative measurements of the beta-particle depth dose distribution for a planar 147 Pm source were determined using an extrapolation chamber (ECH), radiochromic dye films (RDF) and 7 LiF ultra thin thermoluminescence dosemeters (utTLD). The absolute dose estimates provided by the ECH are in excellent agreement with respect to those obtained from RDF dosemeters. In general the agreement between the ECH and the RDF were within 10%. The depth doses initially obtained using 7 LiF utTLD dosemeters assuming the dosemeter centre as the effective point of measurement exhibited an overestimation from 18% for the first 10 mg.cm -2 up to 60% at 30 mg.cm -2 with respect to the ECH measurements. However in this assumption the utTLD estimations neglected the dose gradient inside the dosemeter. In order to take this into account the observed relation between the dose rate measured for each utTLD disc and its corresponding mass thickness was used to calculate the dose rate at the disc surface. A significant improvement in terms of agreement with the absolute measurements was achieved using this approach. The much higher sensitivity of utTLDs compared with ECH and RDF make this technique particularly useful for absorbed dose measurements for low activity beta particle sources.