Podrobný výpis o publikaci

Mass measurements of the nuclides As-69, Se-70,Se-71, and Br-71, produced via fragmentation of a Xe-124 primary beam at the Fragment Separator (FRS) at GSI, have been performed with the multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS) of the FRS Ion Catcher with an unprecedented mass resolving power of almost 1 000 000. Such high resolving power is the only way to achieve accurate results and resolve overlapping peaks of short-lived exotic nuclei, whose total number of accumulated events is always limited. For the nuclide As-69, this is the first direct mass measurement. A mass uncertainty of 22 keV was achieved with only ten events. For the nuclide Se-70, a mass uncertainty of 2.6 keV was obtained, corresponding to a relative accuracy of delta m/m = 4.0 x 10(-8), with less than 500 events. The masses of the nuclides Se-71 and Br-71 have been measured with an uncertainty of 23 and 16 keV, respectively. Our results for the nuclides Se-70,Se-71 and Br-71 are in good agreement with the 2016 Atomic Mass Evaluation, and our result for the nuclide As-69 resolves the discrepancy between the previous indirect measurements. We measured also the mass of the molecule N-14 N-15 Ar-40 (A = 69) with a relative accuracy of delta m/m = 1.7 x 10(-8), the highest yet achieved with an MR-TOF-MS. Our results show that the measured restrengthening of the proton-neutron interaction (delta V-pn) for odd-odd nuclei along the N = Z line above Z = 29 (recently extended to Z = 37) is hardly evident at the N - Z = 2 line, and not evident at the N - Z = 4 line. Nevertheless, detailed structure of delta V-pn along the N - Z = 2 and N - Z = 4 lines, confirmed by our mass measurements, may provide a hint regarding the ongoing approximate to 500 keV discrepancy in the mass value of the nuclide Br-70, which prevents including it in the world average of Ft value for superallowed 0(+) -> 0(+) beta decays. The reported work sets the stage for mass measurements with the FRS Ion Catcher of nuclei at and beyond the N = Z line in the same region of the nuclear chart, including the nuclide Br-70.