Assessment of the environmental exposure at IPEN using CaSO4:Dy detectors with different filters combination

Since the introduction of thermoluminescence (TL) for dosimetric purposes, a lot of efforts have been made to explain and also to improve its application for personal, clinical and environmental dosimetry. To perform environmental and area monitoring at Instituto de Pesquisas Energeticas e Nucleares (IPEN) and in some external institutions and to assess the exposure in these areas, the Thermoluminescent Dosimetry Laboratory has installed several dosimeters spread all over these facilities. The dosimetric system is based on thermoluminescent detectors (TLDs) and on a Harshaw 5500 Automatic TLD Reader that is employed for the readout of the irradiated dosemeters. The TLD consists of CaSO4:Dy sintered discs with 6 mm in diameter and 1 mm in thickness, mounted on a plastic badge, under different metal filters to evaluate and correct the energy dependence of CaSO4:Dy dosemeters. To improve the uncertainties in the environmental exposure evaluation, a new badge with different lead filters arrangement was studied aiming to reduce the TL response of CaSO4:Dy as a function of the incident radiation energy. The main characteristics of the dosimeters such as reproducibility, linearity, dose as a function of the TL response, energy dependence were analysed. The TL dosimeters were calibrated using a gamma radiation 60Co source over the range from 1 to 10mGy. The photon energy dependence response was investigated using an X ray tube operated at a potential of 160kV, with average energy ranging from 33 to 118keV and normalized to 60Co. The results obtained were compared with those one that are normally used to evaluate the environmental exposure at IPEN. The new badge using different lead filters presents good performance and can be used to environmental and area monitoring. (author)