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Abstract |
Neutron-deficient nuclei in the N approximate to Z, A approximate to 90 region were produced by fragmentation of a relativistic 107Ag beam at the GSI Helmholtz Centre for Heavy Ion Research (GSI), separated in the fragment separator FRS, slowed down, and thermalized, and high-precision mass measurements were performed employing the multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS) of the FRS Ion Catcher. The masses of 91,93,95Rh, 89Ru, 88Tc, 87,88,89Mo, and 87,88,89Nb were determined. The mass of 91Rh was measured for the first time. For 89Ru, the measured mass excess deviates by more than ten standard deviations (361 keV) from the previous measurement. A possible misidentification of the measured nuclei, including 89Ru, with contaminants was excluded using a newly developed identification technique for MR-TOF-MS measurements. For the other nuclides, the measured masses agree well with previous measurements. The impact of the new masses on the one-proton separation energy (Sp) of the nuclei with constant total isospin projection (Tz) in the island of inversion around N = Z = 40 is investigated, and signatures of the deformed shell gap at Z = 38 are found. A comparison of the experimental Sp values with the predictions of several mass models shows a general agreement of the trends. |
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