An experiment has been designed to investigate the capability of prompt gamma activation analysis (PGAA) as a method for characterization of nuclear fuel cycle materials. This effort seeks to identify strong neutron capture resonances in the 0.5-40 eV energy region and leverage these resonances to amplify the achievable prompt gamma response via PGAA, often by multiple orders of magnitude. Rare earth element (REE) isotopes are of particular interest: several display strong neutron capture cross sections in the 0.5-40 eV energy region and also remain stable upon neutron capture, making them prime targets for demonstrating the merit of PGAA over the more commonly used delayed gamma activation analysis. The experiment is expected to be conducted at the Detector for Advanced Neutron Capture Experiments (DANCE) at Los Alamos National Laboratory. DANCE is comprised of roughly 160 BaF2 detectors in a spherical geometry at the end of a neutron beam and offers an unparalleled capability to measure the prompt gamma response from an irradiated sample as thoroughly as possible. To aid in the experimental design, a suite of simulation tools is being used to simulate prompt gamma response from a variety of hypothetical samples upon irradiation. The simulation effort for a given isotope follows a workflow which reflects the order of events as they occur in the experimental facility. First, a series of data tools provided by Los Alamos National Laboratory take the beamline geometry, a previously measured neutron flux profile, sample mass, and cross section data to calculate the expected neutron capture reaction rate. Then DICEBOX, an open-source Monte Carlo code that simulates prompt gamma cascades from an excited nucleus, is used to predict prompt gamma production probabilities, which are then normalized per capture event. Combining the previous two steps provides an estimate of the total expected prompt gamma yield from a sample over a known irradiation time. Once the prompt gamma response is predicted, a Geant4 package is used to simulate the gamma transport and subsequent detector response within the detector array. Finally, a provided data analysis tool is used to analyze the Geant4-simulated detector response, which is generated with the same format as an experimentally obtained detector response. Simulations of the complete workflow are currently underway for two isotopes of interest, and the results of this effort will help inform the selection of experimental variables such as irradiation time and sample geometry to maximize the information which may be obtained via gamma spectroscopy. Measurement of relative concentrations of isotopes of interest may allow inferences to be made about geologic provenance and prior neutron fluence through the sample, which alludes to the sample’s processing history.
Year
2024
Abstract