Deep Penetration Calculation Compared with the Shielding Experiments at ISIS

Deep penetration calculations were performed using the intra-nuclear-cascade-evaporation Monte Carlo code, HETC-KFA2, and a one-dimensional Sn code, ANISN, combined with a DLC119/HIL086 multi-group cross section library to compare a shielding experiment at ISIS. In this experiment the reaction rates of 12C(n,2n) in graphite activation detectors have been measured outside the bulk shield, that is 284-cm thick iron and 94-cm-thick concrete, and also outside 119-cm diameter additional shields of 20~120cm thick concrete and 10~60cm thick iron which were newly added to the bulk shield. The secondary neutron spectrum at 90 degree from the tantalum target bombarded by 800 MeV protons was calculated with the HETC-KFA2 code and was used for the source neutrons for a deep penetration calculation. For the Monte Carlo calculation, the geometry of the bulk shield was divided into approximately 100-cm-thick slabs, and step-by-step calculations were carried out for deep penetration in good statistics. 12C(n,2n) reaction rates of the activation detectors behind the bulk shield were calculated, and the comparisons with the measured data showed that the calculation results were underestimated by about 1 order. On the other hand, reaction rates behind additional shields were calculated and attenuation profiles of high energy neutron through concrete and iron shields were compared with the measurement. The calculation gave more than 10% shorter attenuation lengths for concrete and iron shields than the measured results.