AFITBUNKI: A Modified Iterative Code to Unfold Neutron Spectra from Bonner Sphere Detector Data

Abstract : The neutron spectrum unfolding code BUNKI, developed at the Naval Research Laboratory in 1983, was modified to incorporate a finer energy group structure, seven initial-guess spectra, and new dose conversion factors. The modified code, AFITBUNKI, unfolds spectra into 54 energy groups between 10(exp- 7) and 14.92 MeV. The code calculates fluence, absorbed dose, percent of effective dose equivalent, and percent of ambient dose equivalent as a function of neutron energy. Additionally, AFITBUNKI calculates total energy-integrated fluence (phi), absorbed dose (D), dose equivalent (H), effective quality factor (Q), ambient dose (D*), both ICRP Publication 26- and ICRP Publication 60-based ambient dose equivalent (H*) and effective ambient quality factor (Q*), effective dose equivalent (H sub E), effective dose (-E), and the average neutron energy (E). AFITBUNKI uses BUNKI's SPUNIT iterative unfolding algorithm and UTA54, the 171-energy group response matrix developed at The University of Texas at Austin using ENDF/B-IV cross sections collapsed into the 54-group structure. The modified code is verified against spectra unfolded by BUNKIUT and validated against calculations of a NIST fit of 252Cf fission neutrons and against calculations of both D2O- and polyethylene-moderated 252Cf fission neutrons made by Los Alamos National Laboratory's Monte Carlo Neutron-Photon transport code, MCNP.... Neutron unfolding code, Bonner sphere, Neutron dosimetry.