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A systematic study was performed of microsecond γ-decaying isomers around Sn100 produced in a fragmentation reaction of a Xe124 beam at 345 MeV/u at the Radioactive Ion Beam Factory of the RIKEN Nishina Center in Saitama, Japan. Half-lives of isomeric states in that region were remeasured allowing us to improve the currently available experimental information. Reduced transition probabilities were deduced and compared to shell-model calculations in various model spaces. The recently reported low-energy transitions in Rh92 and Ag96 were remeasured with improved precision. Additionally, experimental information on isomeric ratios, including five new ones, were extracted and compared to a previous experimental study and the sharp cutoff model of fragmentation reaction.

7 pags., 4 figs. -- Presented at the Zakopane Conference on Nuclear Physics “Extremes of the Nuclear Landscape”, Zakopane, Poland, August 26–September 2, 2018. -- Open Access funded by Creative Commons Atribution Licence 4.0, The study of nuclei in the region around the N = Z doubly-magic nucleus 100Sn has been of long standing interest for the nuclear structure and nuclear astrophysics. Recently, Park et al. have reported on properties of γ-decaying isomers and isomeric ratios in the vicinity of 100Sn. That experiment was performed at the Radioactive Ion Beam Factory (RIBF) of the RIKEN Nishina Center in Japan as a part of the EURICA campaign. Neutron-deficient nuclei were produced in a fragmentation reaction of a 124Xe primary beam on a 9Be target at an energy of 345 MeV/A. Secondary ions were separated and identified in the BigRIPS fragment separator and implanted in the silicon detector array WAS3ABi. The data presented here were obtained in another experiment performed at the RIBF using the same reaction but slightly different separator settings. New results of ratios of isomeric population and half-lives of γ-decaying isomers populated in the experiment are presented., This work was carried out at the RIBF operated by the RIKEN Nishina Center, RIKEN and CNS, University of Tokyo. The authors acknowledge the EUROBALL Owners Committee for the loan of germanium detectors and the PreSpec Collaboration for the readout electronics of cluster detectors. This work was partly supported by the German BMBF under contract No. 05P12PKFNE and No. 05P15PKFNA and by the U.S. DOE under grant No. DE-FG02-91ER-40609. G.H. is supported by the Bonn–Cologne Graduate School of Physics and Astronomy.

An isomeric state in the proton drip-line nucleus 26 P has been observed by the γ-ray spectroscopy. The γ-ray energy and the half-life are 164.4 ± 0.1 keV and 120 ± 9 ns, respectively. For the isomeric transition of the mirror nucleus 26 Na, the γ-ray energy of 82.40 ± 0.04 keV and the half-life of 4.35 ± 0.16 µs are also revised. Comparing the experimental reduced transition probabilities of 26 Na and 26 P with theoretical ones calcu- lated by the shell model with the USDA interaction, the spin-parity (J π ) of the isomeric state in 26 P is most likely to be 1 + .

A decay spectroscopy experiment was performed within the EURICA campaign at RIKEN in 2012. It aimed at the isomer and particle spectroscopy of excited states and ground states in the mass region below the doubly magic 100Sn. The N = Z nuclei 98In, 96Cd and 94Ag were of particular interest for the present study. Preliminary results on the neutron deficient nuclei 93Ag and 94Ag are presented. In 94Ag a more precise value for the half-life of the ground state’s superallowed Fermi transition was deduced. In addition the energy spectra of the mentioned decay could be reproduced through precise Geant4 simulations of the used active stopper SIMBA. This will enable us to extract Qβ values from the measured data. The decay of 93Ag is discussed based on the observed implantation-decay correlation events.