Speaker
Description
The N=Z=50 isotope $^{100}\text{Sn}$ has long been of interest from theoretical and experimental perspectives because it is the heaviest self-conjugate doubly-magic nucleus. Despite the significant progress in the last decade, the challenge of reaching it in experimental facilities remains to date. Systematic measurements of ground state masses and isomer excitation energies in its vicinity provide important information for understanding the evolution of single-particle states in the N≈Z region and the structure of $^{100}\text{Sn}$ itself.
The FRS Ion Catcher setup (FRS-IC) [1] located at GSI Helmholtz Centre for Heavy Ion Research (Darmstadt, Germany) is specialized in high-resolution direct mass measurements of slowed down and thermalized exotic nuclei produced at relativistic energies. It consists of a cryogenic gas-filled stopping cell (CSC), an RFQ beamline, and a multiple-reflection time-of-flight mass-spectrometer (MR-TOF-MS). Fast ion extraction from the CSC of down to $25 \text{ ms}$ [2] combined with an unprecedented MR-TOF-MS mass resolving power (FWHM) of almost $1,000,000$ provides an exceptional opportunity to measure masses of short-lived exotic nuclei with uncertainties down to $4.0 \cdot 10^{-8}$ [3] and to resolve long-lived nuclear isomeric states, that are challenging to measure with traditional gamma spectroscopy methods. Furthermore, the MR-TOF-MS is broadband i.e., it covers a large mass region of interest which makes it a powerful tool for discovering previously unknown states.
We will discuss the results of direct measurements of ground state masses and isomer excitation energies of $^{97}\text{Ag}$ and odd indium isotopes $^{101-109}\text{In}$. A $(1/2^-)$ isomeric state was discovered in $^{97}\text{Ag}$ with excitation energy of $618(38) \text{ keV}$. Remarkably, this is the first time a nuclear isomer was discovered using an MR-TOF-MS. This discovery was supported by large-scale shell-model and advanced mean-field calculations. The comparison of measured excitation energies with large-scale shell-model calculations, and deduced extrapolations towards $^{99}\text{In}$ – one-proton hole of $^{100}\text{Sn}$ – showed the importance of including core excitations in that region [4]. In addition, other results from this region of the nuclide chart will be presented.
References:
[1] W.R. Plaß et al., Nucl. Instr. Meth. B 317 (2013) 457
[2] S. Purushothaman et al., EPL, 104 (2013) 42001
[3] I. Mardor et al., PRC 103 (2021) 034319
[4] C. Hornung, D. Amanbayev et al., Phys. Lett. B 802 (2020) 135200