Mass measurements of As, Se and Br nuclei and their implication on the proton-neutron interaction strength towards the N=Z line
Creators: name: Mardor, I.
name: Andres, S. Ayet San
name: Dickel, T.
name: Amanbayev, D.
name: Beck, S.
name: Bergmann, J.
name: Geissel, H.
name: Grof, L.
name: Haettner, E.
name: Hornung, C.
name: Kalantar-Nayestanaki, N.
name: Kripko-Koncz, G.
name: Miskun, I.
name: Mollaebrahimi, A.
name: Plass, W. R.
name: Scheidenberger, C.
name: Weick, H.
name: Bagchi, S.
name: Balabanski, D. L.
name: Bezbakh, A. A.
name: Brencic, Z.
name: Charviakova, O.
name: Chudoba, V.
name: Constantin, P.
name: Dehghan, M.
name: Fomichev, A. S.
name: Grigorenko, L. V.
name: Hall, O.
name: Harakeh, M. N.
name: Hucka, J. P.
name: Kankainen, A.
name: Kiselev, O.
name: Knobel, R.
name: Kostyleva, D. A.
name: Krupko, S. A.
name: Kurkova, N.
name: Kuzminchuk, N.
name: Mukha, I.
name: Muzalevskii, I. A.
name: Nichita, D.
name: Nociforo, C.
name: Patyk, Z.
name: Pfutzner, M.
name: Pietri, S.
name: Purushothaman, S.
name: Reiter, M. P.
name: Roesch, H.
name: Schirru, F.
name: Sharov, P. G.
name: Spataru, A.
name: Stanic, G.
name: State, A.
name: Tanaka, Y. K.
name: Vencelj, M.
name: Yavor, M. I.
name: Zhao, J.
Publisher: name: arXiv
Year: 2020
Subjects: subject: Nuclear Experiment (nucl-ex)
subject: Nuclear Theory (nucl-th)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: Mass measurements of the $^{69}$As, $^{70,71}$Se and $^{71}$Br isotopes, produced via fragmentation of a $^{124}$Xe primary beam at the 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. For the $^{69}$As isotope, this is the first direct mass measurement. A mass uncertainty of 22 keV was achieved with only 10 events. For the $^{70}$Se isotope, a mass uncertainty of 2.6 keV was obtained, corresponding to a relative accuracy of $δ$m/m = 4.0$\times 10^{-8}$, with less than 500 events. The masses of the $^{71}$Se and $^{71}$Br isotopes were measured with an uncertainty of 23 and 16 keV, respectively. Our results for the $^{70,71}$Se and $^{71}$Br isotopes agree with the 2016 Atomic Mass Evaluation, and our result for the $^{69}$As isotope resolves the discrepancy between previous indirect measurements. We measured also the mass of $^{14}$N$^{15}$N$^{40}$Ar (A=69) with a relative accuracy of $δ$m/m = 1.7$\times 10^{-8}$, the highest yet achieved with a MR-TOF-MS. Our results show that the measured restrengthening of the proton-neutron interaction ($δ$V$_{pn}$) for odd-odd nuclei at the N=Z line above Z=29 (recently extended to Z=37) is hardly evident at N-Z=2, and not evident at N-Z=4. Nevertheless, detailed structure of $δ$V$_{pn}$ along the N-Z=2 and N-Z=4 lines, confirmed by our mass measurements, may provide a hint regarding the ongoing $\approx$500 keV discrepancy in the mass value of the $^{70}$Br isotope, which prevents including it in the world average of ${Ft}$-value for superallowed 0$^+\rightarrow$ 0$^+$ $β$ 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 $^{70}$Br isotope.
description: 11 pages, 4 figures, accepted for publication at Physical Review C