Epithermal Neutron Activation Analysis at Resonance Energies for Prompt Gamma Activation Analysis at the Penn State Breazeale Reactor

Nick Grenci - The Pennsylvania State University
Brad Nethercutt - The Pennsylvania State University
Marek Flaska - Pennsylvania State University

Many nuclear resonances occur at incident neutron energies above the cadmium cutoff. Resonant cross-sections can span multiple orders of magnitude creating large contrasts of neutron-capture probabilities between isotopes in a sample. Nearly monoenergetic, tunable neutron sources in the energy range where many unique isotopic resonances occur are not currently in existence. A mechanical neutron velocity selection for neutrons between 0.5 – 40 eV has been designed for the Penn State Breazeale reactor and is anticipated to have a 2% energy resolution or better. The energy resolution capability was extensively investigated in observance with isotopic resonance widths in this energy range. Such a source of neutrons is expected to allow for preferential neutron activation at isotopic resonant energies. A nuclear data tool has been created to complement the operation of the mechanical neutron velocity selection system. The development of this tool is an effort to holistically evaluate the resonance structure of all isotopes for which there are ACE files in MCNP6.2. This tool creates a library of data that includes information such as resonant energies, peak height, and FWHM over a user specified energy range. Knowledge gained from the resonance structure is being used to identify samples from the nuclear fuel cycle that could be most sensitive to prompt gamma activation analysis (PGAA). Fuel cycle research, specifically manufacturing processes, are being reviewed. Isotopes that are expected to be present from industrial processes at all stages of the fuel cycle are being tracked. Finally, the nuclear material manufacturing process information will be coupled with the data tool to identify the most sensitive samples that, when interrogated, provide relevant information regarding a fuel cycle process. Fuel cycle research coupled with the data tool to identify isotopes of interest will allow the user to optimize the operating parameters of the chopper system, such as the nominal energy of the neutron pulses and the neutron pulse width. This capability will allow the user to pulse neutrons at resonant energies of specific isotopes thought to be present in a sample, thereby enhancing the resulting signal-to-noise ratio of the isotopes of interest.