Thermal neutron distribution in the beam line tunnel of the KEK electron/positron injector linac

Abstract

The thermal neutron flux distribution formed in the KEK electron/positron injector linac (KEK-linac) tunnel by the positron production beam operation was measured using a gold foil activation technique. The measured data were compared with the calculation results of the PHITS code. The data indicate that the thermal neutrons were locally distributed within a range of 15-20 m of the target position. The thermal neutron flux obtained using the PHITS code reproduced the experimental data at the target location. We obtained coefficient “C” for KEK-linac tunnel from experimental result and calculation as 2.25 that is used in empirical formula to obtain thermal neutron flux, φth = C Q / S, where Q is neutron source intensity, S is the area of tunnel surface.