Abstract
Three high-sensitivity neutron detectors have been set up for monitoring neutrons from the commissioning of a 150-MeV LINAC: the first one is a bare cylindrical He-3 proportional counter with a high sensitivity of ~54 cps/nv to thermal neutrons, the second one uses the same neutron probe but wrapped with 6.5 cm thick polyethylene as a moderator optimized for neutrons in MeV range, the third one is an extended version of the second detector with a layer of lead embedded in the moderator aiming to increase the sensitivity of high-energy neutrons. Their response functions to both neutrons and high-energy gamma rays were calculated using MCNPX. Absolute neutron and gamma-ray spectra at the location of measurement were estimated by FLUKA simulations with a high-fidelity geometry model. Detector responses obtained by folding the spectra with response functions were analyzed and compared with measurements. This paper presents the design and characteristics of these detectors as well as a data analysis of the measured results taken during a full-power LINAC operation.