Benchmark calculations of neutron yields and dose equivalent from thick iron target for 52–256 MeV protons

Neutron yields from thick iron target for 52, 113 and 256 MeV protons were calculated by MCNPX and NMTC/JAM, and compared with data measured by Nakamura et al. and Meier et al. [Nucl. Sci. Eng. 102 (1989) 310]. The MCNPX code reproduced the experimental total neutron yields well by a factor of two, except for 15° at 52 MeV. The NMTC/JAM code also reproduced the experimental total neutron yields by a factor of two, except for 7.5° at 113 MeV, and 52 MeV. Shielding calculations were done for ordinary concrete using the above experimental and calculated neutron spectra. The effective dose distributions using the calculated neutron spectra by both codes were in reasonable agreement with those with the experimental spectra by a factor of about two, except for low emission angles at 113 MeV, and 52 MeV. This discrepancy led to the overestimation of the concrete thickness from 30 to 45 cm and could have a great impact on the construction cost of accelerator facilities. A benchmark calculation of dose equivalent distributions in ordinary concrete for 230 MeV protons reported by Siebers et al. was also performed with MCNPX. The calculated results were in good agreement with the experimental data within a factor of three.