Teste | Abstract: 145-1 | ||||
Abstract:“The International Commission on Radiation Units and Measurements (ICRU) has recently introduced a revised set of operational quantities for personal and area monitoring in their report, ICRU Report 95 [1]. These operational quantities are designed to complement the protection quantities, which are inherently not measurable. To simplify the formalism, the same anthropomorphic phantom used for calculating protection quantities is adopted. However, due to changes in the factors used for converting between protection and operational quantities, personal dosimeters need to be reevaluated or redesigned to account for the altered energy dependence response. Most dosimeters that have been designed for Hp(10) have been shown to overrespond for Hp at low photon energies. This work evaluates the viability to implement a simple modification of the two-element whole-body optical stimulated dosimeter BeOSLTM, from Dosimetrics/Mirion, for the measurement of Hp. This dosimeter badge is composed of two beryllium oxide (BeO) sensitive elements optimized for the evaluation of Hp(10) and Hp(0.07). The algorithm for Hp(10) evaluation is a simple multiplication factor (fEN) of 1.10 to avoid underestimations at low energies due to the lower than tissue-equivalence of the effective atomic number of BeO. This is a standard practice in single-element dosimetry, as the energy to which a user is exposed in a workplace radiation field is always assumed unknown. In this work, an external copper filter was used to cover the Hp(0.07) sensitive element. The nonlinear algorithm used to evaluate Hp consists of dividing the reading MHp10 by 1.10 and averaging with the reading of Cu-filtered MHp0.07. The evaluation of energy dependence was carried in the Radiation Metrology Laboratory (LMRI-DEN/UFPE) on an ICRU slab phantom. The energy range was evaluated in the range of 23 to 164 keV (ISO-N30 to N200) for X-rays and S-Cs-137 (662 keV), with angles varying between 0° and 60°. As result, a maximum deviation for 24 - 662 keV range was found to reduce from 2.25 (Hp evaluation from only the MHp10 reading) to 1.75, which is close to the current IEC limit of 1.60 [2]. In conclusion, this work demonstrated that it is feasible to use filters over the Hp(0.07) sensitive element and a simple nonlinear averaging algorithm to adapt BeOSL dosimeters to the new ICRU 95 Hp quantity for photon dosimetry. More work is still required to optimize the thickness of the filter material. Keywords: ICRU Report 95 , New operational quantities, Adaptation, BeO |