Revision of forensics-relevant nuclear data in Sb 127 β decay
With a half-life of 3.85(5) d, the fission product 127 Sb is potentially useful for the characterization of fallout debris that would be collected for forensic analysis following a hypothetical nuclear event. The β decay of 127 Sb has many characteristic $\gamma$-ray lines, however, the majority of decay strength is concentrated in the three strongest lines near 686, 473, and 784 keV, based on low-precision spectroscopic measurements from decades ago. In a new measurement of 127 Sb β decay, obtained from radiochemical separations of U photofission products, we show that the energies of the 686 and 784 lines are actually shifted lower by 0.8 and 1.1 keV, respectively. Such large discrepancies in the nuclear data inhibit accurate isotopic analyses and have important implications, for example, on the assessment of fission debris that might be collected in the days following a nuclear event. Therefore, a new evaluation of 127 Sb β decay and appropriate revision to the various nuclear databases are warranted. This work reports a new set of $\gamma$-ray energies and relative intensities corresponding to 127 Sb decay.