Precise measurements of the γ-ray intensities following the β decay of long-lived fission products

For national-security applications, such as stockpile stewardship and nuclear forensics, one of the most straightforward and reliable ways to determine the number of fissions that occurred in a chain reaction is to detect the emitted γ rays. The focus of this talk is on our team’s recent measurements to improve the nuclear-decay data needed for several key long-lived fission products. We present high-precision results for the absolute γ-ray emission intensities following the β decays of ¹⁴⁴Ce, ¹⁴⁷Nd, and ¹⁵⁶Eu, reaching <1% precision for the highest-intensity transitions. Our approach consists of implanting fission-product samples into a thin carbon foil using low-energy mass-separated ion beams from the CARIBU facility and then performing β counting using a custom-made 4π gas proportional counter in coincidence with γ-ray spectroscopy using the precisely-calibrated HPGe detector at Texas A&M University.