Calculated neutron and gamma-ray energy spectra from 14-MeV neutrons streaming through an iron duct: comparison with experiment

Abstract

Integral experiments that measure the streaming of approx. 14 MeV neutrons through a 0.30-m-diameter iron duct (L/D approx. 3) imbedded in a concrete shield have been carried out at the Oak Ridge National Laboratory. Calculated and measured neutron and gamma-ray energy spectra are compared at sixteen detector locations on and off the cylindrical axis of the duct. The measured spectra were obtained using an NE-213 liquid scintillator detector with pulse-shape discrimination to simultaneously resolve neutron and gamma ray events. The calculated spectra were obtained using a computer code network that incorporates two radiation transport methods: discrete ordinates (with P/sub 3/ multigroup cross sections) and Monte Carlo (with continuous-point cross sections). The two radiation transport methodologies are required to properly account for neutrons that single scatter from the duct to the detector. The calculated and measured outgoing neutron energy spectra above 850 keV agree within 5 to 50% depending on detector location and neutron energy. The calculated and measured gamma ray spectra above 750 keV are also in favorable agreement, approx. 5 to 50%, depending on detector location and gamma ray energy.