MODIFIED LEAD ATTENUATION METHOD TO DETERMINE THE FAST-NEUTRON SENSITIVITY KU OF A PHOTON DOSIMETER

Various lead attenuation techniques to determine the fast neutron sensitivity ku of a photon dosemeter are reviewed and a modified method is proposed to determine the ku value of a commercially available Geiger-Muller detector. The dependence on the 'effective' photon energy of the gamma -component of the mixed n- Gamma field is illustrated and 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 at the MRC Cyclotron, Hammersmith Hospital, London, show that the Dg component contributes 2.41+or-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 ku value by the Perspex is demonstrated.