Speaker
Description
The semi-magic Sn $(Z = 50)$ isotopes near the neutron mid-shell $(A~= 112\text{–}122)$ exhibit the phenomenon of shape coexistence, in which the proton 2p-2h excitation is associated with the presence of multiple deformed nuclear shapes within a low and narrow range of energies [1]. In recent experiments, thermal neutron capture reactions have been used to study the isotopes $^{116,118}{}{}$Sn [2,3]. The expected $J^\pi = 0^+ \text{ and } 1^+$ capture states allow for direct transitions from the neutron separation energy ($\text{S}_\text{n}$) to lower-lying $0^+$ and $2^+$ levels of interest [2].
We report the progress of our analysis of the $\gamma$-ray spectroscopic data of $^{120}{}{}$Sn produced from the thermal neutron capture an enriched sample of $^{119}{}{}$Sn. The experiment was performed at the Institut Laue-Langevin using the FIPPS spectrometer, which consists of a ring of 8 Compton-suppressed HPGe clover detectors positioned at $90^{\circ}$ to a thermal neutron beamline [4]. Drift corrections were performed with the Cross-Correlation Correction Method [5]. Energy calibrations were performed using known peaks of $^{120}{}{}$Sn as well as high-energy primary $S_n$ transitions of $^{120}{}{}$Sn ($S_n~=~9104.1 \pm 1.1$ keV) and contaminants [6,7].
The calibrated $\gamma$-singles spectrum contains 9.5 billion events and has an energy resolution of 2.5 keV at 1.4 MeV. 14 primary transitions have so far been identified, including those that populate low-lying $0^+$ and $2^+$ states, and we expect to establish new transitions and excited states over a wide range of energies.
[1] P. Garrett et al., Prog. Part, Nucl. Phys. 124, 103931 (2022).
[2] K. Ortner et al., Phys. Rev. C 109, 054317 (2024).
[3] J. L. Pore et al., Eur. Phys. J. A 53, 27 (2017).
[4] F. Wu et al., Phys. Rev. C 111 L051307 (2025).
[5] M. Balogh et al., NIM A 1004, 165368 (2021).
[6] K. Kitao et al., Nucl. Data Sheets 96, 241 (2002).
[7] M. Wang et al., Chinese Phys. C 45, 030003 (2021).