A modified lead attenuation method to determine the fast neutron sensitivity kU of a photon dosemeter

Abstract

Various Pb attenuation techniques to determine the fast neutron sensitivity (.kappa.U) of a photon dosimeter are reviewed and a modified method is proposed to determine the .kappa.U value of a commercially available Geiger-Mueller [GM] detector. The dependence on the effective photon energy of the .gamma.-component of the mixed n-.gamma. field is illustrated. The most probable photon energy is deduced from measurements outside the radiation field. Using the relevant photon mass attenuation coefficient, measurements carried out with a well-collimated neutron beam show the Dg [absorbed dose photon] component contributes 2.41 .+-. 0.13% to the total radiation field. Using a detector with a PTFE sleeve in the place of a Perspex sleeve, highly consistent results are obtained and the enhancement of the .kappa.U value by the Perspex is demonstrated. The neutron sensitivities of 2 MX 163 [Ampercx 18529] GM detectors with Perspex and PTFE sleeves were, respectively, determined as 0.73 .+-. 0.07% and 0.68 .+-. 0.14%.