Direct mass measurements to inform the behavior of $^{128m}$Sb in nucleosynthetic environments

D. E. M. Hoff, K. Kolos, G. W. Misch, D. Ray, B. Liu, A. A. Valverde, M. Brodeur, D. P. Burdette, N. Callahan, J. Clark, A. T. Gallant, F. Kondev, G. E. Morgan, M. Mumpower, R. Orford, W. S. Porter, F. Rivero, G. Savard, N. D. Scielzo, K. S. Sharma, K. Sieja, T. M. Sprouse, L. Varriano

Published PRL 131 262701 (2023)

Nuclear isomer effects are pivotal in understanding nuclear astrophysics, particularly in the rapid neutron-capture process where the population of metastable isomers can alter the radioactive decay paths of nuclei produced during astrophysical events. The $\beta$-decaying isomer $^{128m}$Sb was identified as potentially impactful since the $\beta$-decay pathway along the $A=128$ isobar funnels into this state bypassing the ground state. We report the first direct mass measurements of the $^{128}$Sb isomer and ground state using the Canadian Penning Trap mass spectrometer at Argonne National Laboratory. We find mass excesses of −84564.8(25)  keV and −84608.8(21) keV, respectively, resulting in an excitation energy for the isomer of 43.9(33) keV. These results provide the first key nuclear data input for understanding the role of $^{128m}$Sb in nucleosynthesis, and we show that it will influence the flow of the rapid neutron-capture process.



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