Characterizing special nuclear material (SNM) is critical for nuclear security and non-proliferation. Temporal spectroscopy is a novel and efficient method for characterizing relative material content of special nuclear material. Fission products produced by SNM after being irradiated by a thermal neutron beam can have different half-lives, but can contribute to a similar gamma-ray energy. Temporal spectroscopy analyzes the temporal characteristics of this gamma-ray energy and quantifies the relative mass of 235U and 239Pu.
Real time temporal spectroscopy was successfully conducted at Oregon State University’s TRIGA reactor using a FPGA. A digital to analog converter board (DPP8), developed at OSU, was connected in tandem with the FPGA board to conduct all digital pulse processing needs. Temporal measurements were done by shuttling a sample of between a thermal neutron beam and a HPGe detector. The FPGA provides complete control of the solenoids to shuttle the sample and is also capable of tracking the location of the sample by continuously monitoring optical sensors. A ‘listogram’ module was created to capture temporal slices of a gamma spectrum when the sample was in front of the detector. All digital pulse processing occurs in the FPGA in real-time to maximize flexibility.
Pure samples of natural silver and dysprosium powders were measured to develop reference temporal spectrum. Mixtures of silver and dysprosium, varying from 25% silver/75% dysprosium to 75% silver/25% dysprosium, were measured using the ‘listogram’ module implemented in the FPGA. Relative silver concentrations were estimated to be 62.5% +/- 1.9 % with the actual silver content of 68.2 %.