Precision $\beta $-decay branching ratio measurements for long-lived fission products.

Nuclear data for fission products are used to determine fission-product yields, which impact nuclear applications. Many branching ratio measurements of long-lived fission products (t$_{\mathrm{1/2~}}$\textgreater 1d) suffer from high uncertainties, which contribute to the uncertainties in the determined fission yields. We developed a new experimental method to precisely (\textasciitilde 1{\%} precision) measure the~$\gamma $-ray branching ratios in the~$\beta $~decay of long-lived fission products. The approach involves production of a pure fission-product sample at the CARIBU facility at ANL on an ultra-thin carbon foil and a subsequent decay measurement with a 4$\pi $~gas proportional counter and a meticulously-calibrated high-purity germanium (HPGe) detector at TAMU. We will present results for~$^{\mathrm{95}}$Zr/$^{\mathrm{95}}$Nb,~$^{\mathrm{147}}$Nd, and$^{\mathrm{156}}$Eu.