NAAPRO detector model, a versatile and efficient approach to γ-ray spectrum simulation

The paper describes a detector model which is used by the Neutron Activation Analysis PRognosis and Optimization (NAAPRO) code for modeling γ-ray spectra of the activation products generated by neutron irradiation of hypothetical multielement samples with user-specified composition. Distinctive features of the model are its sufficiently high productivity, flexibility and accuracy, which allow quickly obtaining a model γ-spectrum for a complex energy composition of incident photon flux and arbitrary geometrical dimensions of scintillation (NaI, BGO) or HPGe crystals in a wide continuous range of the detection efficiency (εr=4-250%). Spectrum modeling is carried out based on the physically grounded efficient interpolation schemes for the full-energy peak, single- and double-escape peak efficiencies (as well as for Compton continuum distributions) which were calculated with the use of MCNP (a general purpose Monte Carlo N-Particle transport code) for a wide range of γ-ray energies (5-4 MeV) and distances between source and detector. The influence of scattered photons, of additional absorbing filters, as well as of background conditions during measurement is taken into account in spectrum modeling.