The measurements of neutron energy spectrum at 180 degrees with the mercury target at J-PARC

Spallation neutron production at 180 degrees is of importance for an evaluation of radiation protection for ADS (Accelerator-Driven System) and nuclear physics. It was, however, quite difficult to measure this. We measured the energy spectrum of spallation neutron at 180 degrees at the proton transport beam line (3NBT) to MLF (Materials and Life Science Experimental Facility) on J-PARC using a NE213 liquid scintillator. The irradiated proton energy was 3 GeV, and the intensity was 1 × 10¹⁰ protons. The neutron energy was determined by a Time-Of-Flight method with n-gamma discrimination. We also simulated the energy spectrum by using the PHITS code and compared this with measured spectrum. In this paper, the overview of the experiment and the results are described. (paper)