β-decay of $^{133}In$: a bridge between nuclear structure and astrophysics

Abstract

The β-decay study of indium-133 provides a unique connection between nuclear structure and astrophysics. On one hand, $^{133}In$ is a perfect β-decay demonstrator of r-process nuclei in the vicinity of N=82 owing to its extreme neutron-proton asymmetry and thus large $Q_β$ and $Q_{βn}$ windows. On the other hand, its decay daughter, $^{133}Sn$, features a simple nuclear structure in its ground and excited states due to the proximity to the doubly magic $^{132}Sn$. Thus, a detailed experimental measurement on the β-strength function of $^{133}In$ allows us to unravel the complexities of the decay process in exotic nuclei which are anchored to fundamental elements such as single-particle transitions, and to benchmark the state-of-the-art nuclear models far from the stability with the minimum complexity and ambiguity. This is a crucial step to benchmark nuclear models, predicting the properties of more exotic r-process nuclei that cannot be accessed yet experimentally. An experimental work has been recently conducted at the ISOLDE decay station (IDS), to study the beta decays of $^{133}In$. Uniquely to r-process nuclei, their beta decay involves neutrons and protons in different major shells of opposite parity, dividing the decay strength between forbidden, at low energies, and Gamow-Teller (GT) transitions, mostly unbound states [1]. The new neutron time-of-flight array, INDIe [2-4], was installed at IDS to measure the neutrons emitted from unbound states in $^{133}$Sn following the beta decay of $^{133}In$. Several strong transitions were observed below Ex=6 MeV, including the previously observed state at Ex=3.56 MeV [5-7]. This observation allows us to quantify with high precision the strength distribution of the GT and FF transitions in the region to the southeast of $^{132}Sn$. In addition, we were able to map decay strength up to about 10 MeV excitation energy in $^{133}Sn$, which is crucial to quantify multi-neutron emission probabilities in this region. In this contribution, I will present our latest results regarding the excitation energies, branching ratios, and log-ft of a series of neutron unbound states observed in the decay of $^{133}In$. Our experimental findings were compared to the theoretical predictions. We carried out large-scale shell-model calculations involving several different effective nucleon-nucleon potentials, such as N3LO [6] and $V_{MU}$ [7]. The results of these calculations and comparisons with experimental data will also be discussed. [1] M. Madurga et al., Phys. Rev. Lett 117, 092502 (2016). [2] W.A. Peters et al., Nucl. Inst. Meth. A 836, 122 (2016). [3] S.V. Paulauskas et al., Nucl. Inst. Meth. A 737, 22 (2014). [4] R. Lica et al., in preparation. [5] P. Hoff et al., Phys. Rev. Lett. 77, 1020 (1996). [6] V. Vaquero et al., Phys. Rev. Lett. 118, 202502 (2017). [7] M. Piersa et al., Phys. Rev. C 99, 024304 (2019). [8] D.R. Entem, et al., Phys. Rev. C 68, 041001 (2003). [9] T. Otsuka et al., Phys. Rev. Lett. 104, 012501 (2010). Download Abstract