Measurement and simulations of high-energy neutrons through a various thickness of concrete and steel shields using activation detectors at CHARM and CSBF

A shielding experiment using activation detectors was performed at the CERN High-energy AcceleRator Mixed-field (CHARM) facility and the CERN Shielding Benchmark Facility (CSBF). The protons (24 GeV/c) were bombarded into a 50-cm-thick copper target, and the released neutrons were transmitted through various shields located vertically upward from the target. Ordinary concrete slabs of 40- to 160-cm thicknesses and steel slabs of 20- to 80-cm thicknesses were installed by changing the material and the thickness of the shield. Activation detectors of bismuth, indium, aluminum, and graphite were variously placed in these shields and activated by high energy neutrons. From the radionuclide production rate in the activation detectors, the attenuation profiles through the various shielding materials were obtained for the reactions of Bi-209(n,xn)Bi210-x(x = 4-9), In-115(n,n')In-115m, Al-27(n,& alpha;)Na-24, and C-12(n,2n)C-11. Estimated attenuation lengths of high energy neutrons through concrete and steel were compared with cited data and discussed. Monte Carlo simulations using FLUKA, PHITS, and GEANT4 were also performed as benchmark calculations, and they agreed with the experimental data, generally within a factor of 2.