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

The measurements and calculations have been made for 0 20 moderated 252Cf spherical assembly of diameter 30 em 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 ENOF/B-IV and ENOF/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 0 20 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 H20 admixture has been calculated. The results indicate generally better agreement of measurements and calculations using ENOF /B-VI data than using ENOF / B-IV. Nevertheless, some differences between measurements and calculations with ENOF /B-VI in certain energy regions were still observed if the measurements were repeated with different spectrometers.