Measurements of Neutron Attenuation through Iron and Concrete at ISIS

Abstract

A deep penetration experiment through a thick bulk shield was performed at an intense spallation neutron source facility, ISIS, of the Rutherford Appleton Laboratory. ISIS is an 800MeV-200 μ A proton accelerator facility. Neutrons are produced from a tantalum target, and are shielded with approximately 3m thick iron and 1 m thick ordinary concrete. On the top of the shield, we measured the neutron flux attenuation through concrete and iron shields which were additionally placed up to 1.2 m and 0.6 m thicknesses, respectively, using activation detectors of carbon, aluminum and bismuth, and also indium-loaded multi-moderator spectrometer. The dose attenuation was simultaneously measured with the neutron and photon survey meters. The attenuation lengths of concrete and iron for high energy neutrons above 20MeV were obtained from the 12C(n,2n) reaction of carbon, and the neutron spectra penetrated through the additional shield and on the target shield top were obtained from the 12C(n,2n), 27Al(n,α) and 209Bi(n, xn) reactions, and multi-moderator spectrometer.We are now analyzing the measured results to compare with the shielding calculation.