Speaker
Description
Exotic, neutron-rich nuclei are a testing ground for the evolution of nuclear structure away from stability [1]. As radioactive beam facilities extend isotope production toward the neutron dripline [2-3], it is paramount that experimental efforts follow into this less-explored region of the nuclear chart to fully exploit its discovery potential. In these nuclei, beta-delayed single- and multi-neutron emission often dominates decay paths toward stability [1]. Neutron spectroscopy combined with gamma-ray measurements is necessary to uncover the full picture. Nuclei such as those southeast of 132Sn in the chart of nuclides are less affected by the typical experimental challenges of neutron detection; studying the decays of near-doubly magic nuclei simplifies the analysis, as they populate nuclei with low nuclear level densities and strong single-particle character. In this regard, I will present results from the beta-delayed neutron spectroscopy of 134In performed at the ISOLDE Decay Station at CERN [4], using the Neutron dEtector with multi-neutron (Xn) Tracking (NEXT) array [5-6]. For the first time, energy correlations in two-neutron emission were exploited as a probe for nuclear structure. In the two-neutron emission channel from 134Sn, the population of the long-sought i13/2 neutron single-particle state was observed as an intermediate step, thereby pinning down the energy of the final elementary excitation in 133Sn between the N = 82 and 126 shell closures [7-10]. Furthermore, we find a significant discrepancy between the experimental neutron-branching ratios to this state and the predictions of the Hauser-Feshbach statistical model for spherical neutron emitters [11-12]. This result indicates that the Bohr assumption of the immediate formation of a compound nucleus following beta decay is not valid in this case and should be revisited, with important implications for future experimental studies.
References:
[1] M. R. Mumpower et al.; Progress in Particle and Nuclear Physics, 86 86-126 (2016)
[2] R. Catherall, W. Andreazza, M. Breitenfeldt, A. Dorsival et al.; J. Phys. G 44, 094002 (2017)
[3] V. Fedosseev, K. Chrysalidis, T. Day Goodacre, B. Marsh et al.; J. Phys. G 44, 084006 (2017)
[4] P. Dyszel, R. Grzywacz, Z. Y. Xu et al.; Phys. Rev. Lett. 135, 152501 (2025)
[5] J. Heideman et al.; Nuc. Instrum. Methods Phys. Res. A 946, 162528 (2019)
[6] S. Neupane et al.; Nuc. Instrum. Methods Phys. Res. A 1020, 165881 (2021)
[7] P. Hoff, P. Baumann, A. Huck; Hyperfine Interactions 129, 141 (2000)
[8] A. Korgul et al.; EPJ A 7, 167 (2000)
[9] K. Jones et al.; Nature 465, 454 (2010)
[10] J. Allmond et al.; Phys. Rev. Lett. 112, 172701 (2014)
[11] W. Hauser and H. Feshbach; Phys. Rev. 87, 366 (1952)
[12] C. Pruitt, J. E. Escher, R. Rahman; Phys. Rev. C 107, 014602 (2023)