Speaker
Description
The region of neutron-deficient nuclei around $A\approx90$ and near the $N \approx Z$ line exhibits rapid changes in nuclear structure, including shape coexistence and strong proton-neutron correlations. These nuclei provide key insights into shell evolution, deformation effects, and the underlying nuclear interactions, and serve as important benchmarks for theoretical models.
In this work, we present recent mass measurements of neutron-deficient Ru and Pd isotopes performed at the FRS Ion Catcher (FRS-IC) at GSI. The experiments combine in-flight separation of projectile fragments with stopping in a cryogenic stopping cell (CSC) and high-resolution measurements using a multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS), allowing access to nuclei with low yields and short half-lives.
Recent measurements include a direct mass measurement of $^{89}\mathrm{Ru}$, showing that the measured value deviates by more than 10 standard deviations (361(35) keV) from the previous result, while misidentification has been excluded using advanced identification techniques. This provides a reliable basis for extracting one-proton separation energies and reveals structural effects consistent with a deformed subshell gap near $Z = 38$.
Furthermore, the mass of $^{93}\mathrm{Pd}$ was measured directly for the first time, reducing the uncertainty by an order of magnitude. In combination with available spectroscopic information and decay data, these results indicate that the excitation energy of the parent state associated with the one-proton (1p) and two-proton (2p) decay branches in $^{94}\mathrm{Ag}$ differ by about 10 standard deviations, indicating that these decay modes do not originate from the same nuclear state. This finding calls into question the proposed decay scheme of two-proton decay and suggests the presence of multiple structurally distinct high-spin configurations, challenging previous interpretations of decay mechanisms in this region.