Comparison of measured and calculated neutron transmission through heavy water for Cf-252 source placed in the center of 30 cm diameter sphere

The measurements and calculations have been made for D2O moderated Cf-252 spherical assembly of diameter 30 cm which has been adopted as a calibration standard for the testing of personal neutron dosimeters. The leakage neutron spectrum has been measured in the energy range from 0.1 to 10 MeV using a proton recoil spectrometer and compared with MCNP calculations with ENDF/B-IV and ENDF/B-VI nuclear data files. The experimental and calculational results were compared also with the earlier reference data recommended by ISO. The Cf sources were placed to the center of D2O sphere in a channel of diameter 8 or 25 mm. The dependence of leakage neutron spectrum on channel diameter was measured and calculated. The influence of H2O admixture has been calculated. The results indicate generally better agreement of measurements and calculations using ENDF/B-VI data than using ENDF/B-IV. Nevertheless, some differences between measurements and calculations with ENDF/B-VI in certain energy regions were still observed if the measurements were repeated with different spectrometers. (C) 1997 Elsevier Science Ltd.