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In a recent article published in "Physical Review Letters", M. Wang et al. report on high-precision mass measurements of upper fp-shell N=Z−2 and N=Z−1 nuclei. The experiment was performed at the Heavy Ion Research Facility in Lanzhou (HIRFL)  (China). Using a novel method of isochronous mass spectrometry, the masses of ⁶²Ge, ⁶⁴As, ⁶⁶Se, and ⁷⁰Kr were measured for the first time, and the masses of ⁵⁸Zn, ⁶¹Ga, ⁶³Ge, ⁶⁵As, ⁶⁷Se, ⁷¹Kr, and ⁷⁵Sr were redetermined with improved accuracy.

The new masses allowed to derive residual proton-neutron interactions (δV_pn) in the N=Z nuclei, which are found to decrease (increase) with increasing mass A for even-even (odd-odd) nuclei beyond Z=28. This observed bifurcation of δV_pn could not be reproduced by available mass models.
Ab initio calculations using the chiral nuclear force with three-nucleon interaction included could reproduce the bifurcation. However, for odd-odd N=Z nuclei δV_pn is systematically overestimated. This implies that state-of-the-art ab initio approaches need further improvement, and accurate masses of nuclei along N=Z provide an important testing ground.

Please read more in the article ... >

New nuclear physics data provide a better understanding of the properties of neutron stars. High-precision measurements of nuclear masses reveal germanium-64 as a waiting-point nucleus in nucleosynthesis via fast proton capture and form the basis for modelling X-ray bursts on neutron stars as part of binary systems.

The experiments performed by the Storage Ring Nuclear Physics Group  at the Heavy Ion Research Facility in Lanzhou (HIRFL)  (China) as well as the interpretation of the data were supported by researchers from our "Stored and Cooled Ions" division at the MPIK in Heidelberg and the ASTRUm group  at GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt within a cooperation successfully ongoing for more than 10 years.

Please read more in the "Nature Physics" article .

Further information also in the press release of the MPIK .