Speaker
Description
The semi-magic Sn ($Z$ = 50) isotopes with neutron numbers extending from $N$ = 50 to beyond the $N$ = 82 shell, provide an important testing ground for studying the evolution of nucleon–nucleon interactions across the chain. Although ground states of Sn isotopes are predominantly spherical, mid-shell isotopes ($A$ = 112–122) display shape coexistence associated with proton 2p–2h intruder configurations, leading to deformed rotational bands built upon excited 0$^+$ states [1]. Recent studies have suggested different bandheads for these intruder structures, namely 0$^+_2$ state in $^{118}$Sn and the 0$_3^+$ state in $^{116}$Sn [2,3]. This motivates a detailed spectroscopic investigation of the neighboring nucleus $^{114}$Sn to clarify the bandhead of the shape-coexisting structure and to search for possible bands built upon the 0$_3^+$ state. Furthermore, recent theoretical and experimental studies have proposed the presence of pygmy quadrupole resonance (PQR) in $^{112,114,124}$Sn, although its existence is yet to be firmly established [4,5].
We report on a comprehensive $\gamma$-ray spectroscopy study of $^{114}$Sn following the $\beta$ decay of $^{114}$Sb, produced at the TRIUMF–ISAC facility. The resulting $\gamma$ rays were detected using the GRIFFIN spectrometer, consisting of 15 Compton-suppressed HPGe clover detectors with a total of 60 crystals, facilitating angular correlation measurements. Ancillary detectors included the Zero Degree Scintillator (ZDS) for $\beta$ tagging and the PACES array of five Si(Li) detectors for conversion-electron spectroscopy. In addition, eight LaBr$_3$(Ce) detectors were employed for lifetime measurements using fast-timing techniques.
In this work, more than 600 new $\gamma$-ray transitions and over 100 new excited states have been established in $^{114}$Sn. The results confirm the 0$_2^+$ state as the bandhead of deformed 2p-2h band, in contrast to $^{116}$Sn. The implications for the evolution of shape-coexisting structures near the neutron mid-shell and low-lying quadrupole strength in this region will be discussed at the conference.
[1] P. Garrett et al., Prog. Part. Nucl. Phys. 124, 103931 (2022).
[2] K. Ortner et al., Phys. Rev. C 102, 024323 (2020).
[3] J. L. Pore et al., Eur. Phys. J. A 53, 27 (2017).
[4] M. Spieker et al., Phys. Lett. B 752, 102–107 (2016).
[5] N. Tsoneva et al., Nucl. Phys. A 990, 183–198 (2019).