S. Padgett

Validation of a Monte Carlo HPGe detector model against irradiated foil gamma-ray spectroscopy measurements

A high-purity germanium detector Monte Carlo model was evaluated for its ability to predict activation product ratios in Fe, Cr, Ni, and stainless-steel foils. To evaluate the model, activation product ratios calculated from simulated gamma-ray spectra were compared against those from experiment measurements. Analysis shows that the detector model accurately predicts activation product ratios within 10% when free of interferences. Presence of a shield chamber greatly increases computation time, but does not provide any quantitative advantages. Overall, the model is useful for predicting activation product ratios and experiment planning.

FIER: Software for analytical modeling of delayed gamma-ray spectra

Abstract A new software package, the Fission Induced Electromagnetic Response (FIER) code, has been developed to analytically predict delayed γ -ray spectra following fission. FIER uses evaluated nuclear data and solutions to the Bateman equations to calculate the time-dependent populations of fission products and their decay daughters resulting from irradiation of a fissionable isotope. These populations are then used in the calculation of γ -ray emission rates to obtain the corresponding delayed γ -ray spectra. FIER output was compared to experimental data obtained by irradiation of axa0 235 U sample in the Godiva critical assembly. This investigation illuminated discrepancies in the input nuclear data libraries, showcasing the usefulness of FIER as a tool to address nuclear data deficiencies through comparison with experimental data. FIER provides traceability between γ -ray emissions and their contributing nuclear species, decay chains, and parent fission fragments, yielding a new capability for the nuclear science community.

Comparison of irradiated foil measurements with activation calculations and HPGe simulations

Theoretical activation calculations for Fe, Ni, and stainless steel foils were compared against irradiated foil measurements from a critical assembly. Calculated/experiment values spanning 0.62–1.31 showed that the restricted approach used here is insufficient for experiment planning, with the collapsed cross-section being the primary source of error. The effect of decay time on gamma-ray spectroscopy measurement reliability was investigated using a Monte Carlo HPGe detector model. Simulations showed no correlation with decay time, absent interferences. Specific interferences for Fe-59 (Ni) and Co-60 (stainless steel) activation product ratios suggested optimal measurement windows having respective decay times of 9–11xa0days and 4–7xa0days.

Retrospective neutron spectrum determination of a (30 MeV D, Be) source using the multi-foil activation technique and STAYSL-PNNL

Retrospective characterization of a (30xa0MeV D, Be) neutron source was performed employing multi-foil activation and STAYSL-PNNL. Experimental reaction rates were calculated from gamma spectroscopy measurements of irradiated foils and MCNP provided the guess spectrum. Adjusted spectra were evaluated through activation calculations for a stainless-steel target using FISPACT-II. Adjusted spectra showed limited dependence on the dosimetry reactions and provided minor improvements in activation calculations. Omitting reflected neutrons in the guess spectrum generated poor activation results and the limited number of dosimetry reactions introduced doubt in the adjusted spectra. A dedicated neutron spectrometry experiment and a more detailed simulation is required.