Precise measurements of gamma-ray intensities for long-lived fission products

We recently demonstrated a new experimental approach to precisely determine the gamma-ray intensities following the beta 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 done through detection of the emitted gamma rays. The focus of this talk is on recent measurements to improve the nuclear-decay data for the fission products ⁹⁵Zr, ¹⁴⁴Ce, and ¹⁴⁷Nd. 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 beta counting using a custom-made 4-pi gas proportional counter in coincidence with gamma-ray spectroscopy using the precisely-calibrated HPGe detector at Texas A&M University. Recent results for ⁹⁵Zr, ¹⁴⁴Ce, and ¹⁴⁷Nd will be presented and future plans will be discussed.