Fast Thermal Increment Yield Ratios and Their Use to Identify Fissile and Fertile Compositions of Uranium Material

A novel nondestructive assay technique for uranium enrichment verification using delayed gamma-ray spectroscopy is presented. This method leverages distinct fission product yield signatures from the thermal neutron–induced fission of 235U and fast neutron–induced fission of 238U, induced using a compact 5-Ci 241Am-Be source. We introduce the fission yield increment ratio (FYIR), a metric derived from the apparent fast and thermal fission yields of key isotopes: 92Y, 91Sr, 92Sr, 88Kr, 105Ru, and 101Tc. The analytical expressions demonstrate that both the FYIR value and its statistical variability across a set of fission products correlate directly with uranium enrichment. This approach offers a practical and effective tool for verifying fissile and fertile content in uranium materials for nuclear safeguards.