Deep-penetration calculation with an 800 MeV proton beam compared with the shielding experiment at isis

A calculation of neutron penetration through a thick shield was performed with a three-dimensional multi-layer technique using the MARS14 Monte Carlo code to compare with the existing experimental data for the ISIS spallation neutron source facility shielding. In the calculation, secondary neutrons from a tantalum target bombarded by 800 MeV protons were transmitted through a bulk shield of approximately 3 m thick iron and 1 m thick concrete. The geometry of the bulk shield was divided into several layers about 50 cm thick, and a step-by-step calculation was carried out to multiply the particles at the boundaries between the layers. Finally, the energy spectra of high-energy neutrons behind the bulk shield were obtained with good statistics. Corresponding 12C(n,2n) reaction rates which agree with the experimental data within 30% were also obtained. (author)