Heinrich Eder1, Helmut Schlattl2. 1. Formerly Bavarian Environment Agency, Am Stadtpark 43, 81243 Munich, Germany. Electronic address: eder-h@arcor.de. 2. Helmholtz Zentrum München, German Research Center for Environmental Health, Institute of Radiation Protection, Ingolstädter Landstrasse 1, 85764 Neuherberg, Germany. Electronic address: helmut.schlattl@helmholtz-muenchen.de.
Abstract
PURPOSE: Lead free protective clothing can create a higher part of secondary radiation (SR) than products that are based on lead. Hence, the attenuation properties may be downgraded. The international measuring standard IEC 61331-1:2014 declares the "inverse broad beam geometry" (IBG) as standard method, which has recently been modified to IBG∗ by the Physikalisch Technische Bundesanstalt (PTB). Because of the unspecific partial irradiation of the ionization chamber problems in the evaluation of lead equivalence values (LEVs) can occur. An alternative method proposed in this paper overcomes these problems. MATERIALS AND METHODS: The alternative setup "modified broad beam geometry" (BBG∗) was tested and compared to the IBG∗ method by performing Monte Carlo simulations and radiation measurements including several lead-composite and lead-free protective materials. RESULTS: Simulations show a reduced collection efficiency of SR under IBG∗ whereas BBG∗ features a high degree of SR collection. Material samples with a high amount of SR can feature up to 8% higher LEVs compared to IBG∗. For most of the currently salable materials the differences of BBG∗ vs IBG∗ amount to <3% (0.25 mm LEV) and <1% (0.50 mm LEV). In special cases the currently practiced method can lead to heavier protective clothings. CONCLUSIONS: The proposed BBG∗ setup meets the specifications of the IEC standard with respect to energy response and SR collection. The method should be implemented in the IEC standard.
PURPOSE: Lead free protective clothing can create a higher part of secondary radiation (SR) than products that are based on lead. Hence, the attenuation properties may be downgraded. The international measuring standard IEC 61331-1:2014 declares the "inverse broad beam geometry" (IBG) as standard method, which has recently been modified to IBG∗ by the Physikalisch Technische Bundesanstalt (PTB). Because of the unspecific partial irradiation of the ionization chamber problems in the evaluation of lead equivalence values (LEVs) can occur. An alternative method proposed in this paper overcomes these problems. MATERIALS AND METHODS: The alternative setup "modified broad beam geometry" (BBG∗) was tested and compared to the IBG∗ method by performing Monte Carlo simulations and radiation measurements including several lead-composite and lead-free protective materials. RESULTS: Simulations show a reduced collection efficiency of SR under IBG∗ whereas BBG∗ features a high degree of SR collection. Material samples with a high amount of SR can feature up to 8% higher LEVs compared to IBG∗. For most of the currently salable materials the differences of BBG∗ vs IBG∗ amount to <3% (0.25 mm LEV) and <1% (0.50 mm LEV). In special cases the currently practiced method can lead to heavier protective clothings. CONCLUSIONS: The proposed BBG∗ setup meets the specifications of the IEC standard with respect to energy response and SR collection. The method should be implemented in the IEC standard.