Ponente
Descripción
The discovery of the most neutron-deficient nuclei in the $^{100}$Sn region has opened possibilities for new and more precise spectroscopy experiments, especially in light of the increased primary beam intensity of $^{124}$Xe at RIKEN RIBF and a combined array of HPGe detectors for high $\gamma$-ray efficiency. The three major topics are presented below.
Shell model calculations showed a staggered decrease in the proton separation energies for both $^{92}$Ag and $^{96}$In, which were discovered in a previous EURICA experiment. Sufficiently long half-lives are hypothesized, where proton emission is delayed by the $l = 4$ centrifugal barrier of the $\pi g_{9/2}$ orbital. The half-life of $^{93}$Ag was deduced to be 228(16) ns, based on a fraction of nuclei that survived the flight through BigRIPS and the ZeroDegree spectrometer. On the other hand, a hypothetical proton-unbound isomer in $^{97}$In was previously suggested. First proton decay spectroscopy of $^{92,93}$Ag and $^{96,97}$In will enable new measurements of mass differences in these dripline nuclei and enrich theories on proton emission. Furthermore, potentially new $p$-delayed $\gamma$-ray data may be obtained to unveil new excited states in $^{91,92}$Pd and $^{95,96}$Cd.
In light of the series of lifetime measurements of all but the $2^{+}$ state in $^{98}$Cd, the test of isospin symmetry in $^{98}$Sn is more essential than ever. It is the unique candidate for measuring both the energy and the $B(E2)$ values to complete the heaviest pair of semi-magic mirror nuclei in the nuclear chart. The structure of $^{98}$Sn is predicted to possess a long-lived $8^{+}$ state ranging from a few hundred ns to 5$\mu$s, decaying by an $E2$ transition of approximately 100 keV. The low production rate of $^{98}$Sn is compensated by the high isomeric ratio of the $8^{+}$ seniority isomers in the $^{100}$Sn region, and a high survival probability through the spectrometer due to its long lifetime and significant internal conversion coefficient. Coupled to the high-efficiency HPGe array, prospects for discovering new delayed $\gamma$ rays in this nucleus are very high. Isospin symmetry will be tested via comparisons of $E_x(J^{\pi})$ and $B(E2)$ values with $^{98}$Cd.
Finally, the reduced $B_{GT}$ value of $^{100}$Sn in the latest EURICA experiment, owing to a $3\sigma$ increase in the $\beta$-decay endpoint energy ($Q_{\beta}$), was met with mixed reception in the follow-up mass spectroscopy and colinear laser spectroscopy experiments on the neighboring nuclei. The level scheme of $^{100}$In, which affects the $Q_{\beta}$ and $B_{GT}$ values, remains uncertain due to unobserved $\gamma$-ray transitions relative to SM predictions. The efficiency of EURICA in the previous $^{100}$Sn decay spectroscopy experiment was much reduced relative to its full capacity. The new HPGe array is expected to be 3-4 times more efficient, leading to an improvement in $\gamma$-ray singles and $\gamma$-$\gamma$ coincidence statistics by several factors and an order of magnitude, respectively. The ambiguity surrounding the level scheme of $^{100}$In will be fully addressed by clear $\gamma$-$\gamma$ coincidence and anti-coincidence relationships.
