Measurement of deep penetration of neutrons produced by 800-MeV proton beam through concrete and iron at ISIS

A deep penetration experiment through a thick bulk shield was performed at an intense spallation neutron source facility, ISIS, of the Rutherford Appl eton Laboratory (RAL), UK. ISIS is an 800 MeV-200 muA proton accelerator fa cility. Neutrons are produced from a tantalum target, which is shielded wit h approximately 3-m thick iron and I-m thick ordinary concrete in the upwar d direction. On the top of the shield, we measured the neutron flux attenua tion through concrete and iron shields which were additionally placed up to 1.2-m and 0.6-m thicknesses, respectively, using the activation detectors of graphite, bismuth, aluminum and the multi-moderator spectrometer inserte d indium. The attenuation lengths of concrete and iron for high-energy neut rons above 20 MeV produced at 900 to the proton beam were obtained from the C-12(n, 2n)C-11 reaction rates of graphite. The neutron spectra through co ncrete and iron were obtained by the unfolding analysis of the reaction rat es of the C-12(n, 2n)C-11, Al-27(n, alpha)Na-24, Bi-209(n, chin)Bi-210 (chi = 4-10) and In-115(n, gamma)In-116m in the energy range of thermal to 400 MeV. (C) 2001 Elsevier Science B.V, All rights reserved.