Improvement of the response of a rem-meter based on prompt gamma ray detection to high-energy neutrons up to 1 GeV

Prompt gamma emissions from a system containing Borated High Density Polyethylene (BHDPE) covered by lead (Pb) have been estimated for incident neutron energies from 0.01 eV up to 1 GeV using the FLUKA Monte Carlo simulation code. The areas under the photo peaks of the emitted prompt gammas are linearly combined to approximate the ICRP recommended energy dependent neutron dose conversion coefficients to estimate the neutron ambient dose equivalent. An enhancement in the prompt gamma emission is observed in the system above 14 MeV of incident neutron energy because of neutron multiplication due to (n, xn) reactions in Pb. Monte Carlo simulation results are used to optimize the thickness of the Pb-cover and the boron content in BHDPE. Different workplace neutron spectra are used to computationally validate the present method. The photo peak areas from different prompt gammas emitted from H, B, C and Pb in the proposed system, when multiplied with appropriate coefficients and summed, can predict neutron ambient dose equivalent with good accuracy for both high energy (up to 1 GeV) and low energy (down to 0.01 eV) neutrons.