Revision of forensics-relevant nuclear data in Sb-127 beta decay

With a half-life of 3.85(5) d, the fission product Sb-127 is potentially useful for the characterization of fallout debris that would be collected for forensic analysis following a hypothetical nuclear event. The beta decay of Sb-127 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 Sb-127 beta 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 Sb-127 beta decay and appropriate revisions to the various nuclear databases are warranted. This paper reports a new set of gamma-ray energies and relative intensities corresponding to Sb-127 decay.