Precision β-decay branching ratio measurements for long-lived fission products*

One of the most straightforward and reliable ways to determine the number of fissions that occurred in a chain reaction is via detection of  the characteristic γ rays emitted during the β-decay of the fission products. These γ rays are emitted in only a fraction of the decays, and this fraction must be known accurately to determine the total number of fissions. Many measurements of the β-decay of the long-lived fission products suffer from high uncertainties (even up to 20%) which contributes to the uncertainties in the determined fission yields. We have developed a novel technique to measure (<1% precision) γ-ray intensities and β-decay branching ratios. Our technique takes advantage of radioactive beams from CARIBU facility at Argonne National Lab to produce ultra-pure radioactive samples of fission products, and a nearly 100% efficient 4π β-spectrometer paired with the painstakingly calibrated γ-ray detector [1]. The results of the branching ratios of ⁹⁵Zr, ¹⁴⁴Ce, and ¹⁴⁷Nd will be presented. 

[1] R. G. Helmer, J. C. Hardy, V. E. Iacob, M. Sanchez-Vega, R.G. Neilson, and J. Nelson, NIM Phys. Res., Sect. A 511, 360 (2003).