Estimation of neutron energy distributions from measured prompt gamma intensities: Experimental validation

Abstract

The technique for estimating the incident neutron energy distribution from emitted prompt gamma intensities from a system placed in a neutron field is validated using experimental data. A cylinder of high density polyethylene (HDPE) kept inside another cylinder of borated HDPE (BHDPE) placed in a neutron beam and the prompt gamma emissions are detected using a lead shielded NaI(Tl) detector based spectrometer system. The experiments were carried with an isotopic 241Am-Be neutron source kept inside a thick concrete bunker. The measured photo peak intensities are used to unfold the incident neutron energy distribution using the calculated response functions of the system and the genetic algorithm based Monte Carlo de-convolution code GAMCD. The technique could successfully unfold the neutron spectra above 1 MeV and estimate the integral neutron fluence below 1 MeV. The covariance and the correlation matrices involving the energy groups in the solution spectrum were computed using the results from different Monte Carlo histories.