A new card holder for personal X and gamma dosimetry

Abstract

The aim of this work is the description of the new card holder developed at the Dosimetry Service of the University Hospital in Firenze, specifically designed for medical occupational exposure measurements. The basic dosimeter (card), already in use at the Dosimetry Service, contains two LiF100 detectors, the second one being filtered to get energy response correction. The rationale for a new holder was both the agreement to the statements of the Italian law promoted after to the BSS Directive [Council Directive 96/29/EURATOM of 13 May 1996 laying down basic safety standards for the protection of the health of workers and the general public against the dangers arising from ionizing radiation.] and the practical need of dosimeter which is easy to handle. Therefore, robustness, ease of sliding in and pulling out the card, feasibility of applying a personal identification label, etc. were goals to achieve, as well as increasing the efficiency of the service. The work describes the response of the whole dosimeter (card and holder) to the incident radiation. The Italian National law, derived from BSS European Directive [Council Directive 96/29/EURATOM of 13 May 1996 laying down basic safety standards for the protection of the health of workers and the general public against the dangers arising from ionizing radiation.], states that individual dosimeters must measure H p ( 10 ) for the monitoring of occupationally exposed workers, so the main goal of our work was to reach optimum response in terms of H p ( 10 ) . However, the dosimeter was also designed to allow the measurement of H p ( 3 ) , for monitoring eye lens doses, and of H p ( 0.07 ) , to measure weakly penetrating radiation fields. The test procedure was performed according to international ISO standard [ISO 4037-1, ISO 4037-2, ISO 4037-3, 1996. — X and gamma reference radiation for calibrating dosimeters and dose-rate meters and for determining their response as a function of photon energy.]. We also tested the response in terms of H * ( 10 ) for environmental monitoring with the same procedure. Calibrated beams for our test were provided by the testing facility located at the Institute of Radioprotection of the ENEA Section in Bologna. A final holder design was arrived after many test repetitions with different filter thicknesses and holder shapes. Aluminium filter, 1.5 mm thick, resulted in the best compromise between sensitivity and energy discrimination effectiveness. The conic-hole shape of the holder around the unfiltered detector gives good results even at wide angles of incidence of radiation. Dosimeter performances in terms of H p ( 10 ) are consistent with the tolerance limits established from international ISO standard [ISO 14146, 2000. Radiation protection—Criteria and performance limits for the periodic evaluation of processors of personal dosimeters for X and gamma radiation.]. Good results were consistently achieved in terms of H p ( 3 ) , H * ( 10 ) and H p ( 0.07 ) . However, out of the tolerance results were found for H p ( 0.07 ) at angles of incidence greater than 60 ∘ and energies lower than 20 keV.