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Experimental observables of simple atomic systems with a single or few electrons, such as atomic and molecular hydrogen, helium, and their ions, enable extremely precise tests of the standard model of physics. The properties of the fundamental particles, such as the mass of the electron and the mass and charge radius of the light nuclei, are thus of importance for fundamental physics.
The LIONTRAP (Light ION TRAP) experiment, situated at Johannes Gutenberg University (JGU) in Mainz, Germany, is a dedicated high-precision Penning-trap mass spectrometer aiming for most precise mass measurements on various light ions.

In a recent article published in "Physical Review Letters", S. Sasidharan et al. report on a 12 parts-per-trillion measurement of the mass of a ⁴He²⁺ ion using LIONTRAP. From the ion mass m(⁴He²⁺), the atomic mass of the neutral atom was determined without loss of precision: m(⁴He) = 4.002 603 254 653(48) u.
This result is slightly more precise than the current CODATA18 literature value but deviates by 6.6 standard deviations.
To further investigate the inconsistencies in the light ion mass regime, a re-measurement of the ³He/¹²C mass ratio using LIONTRAP is planned.

Please read more in the article ... >

Further information also in the press releases of the MPIK  and the GSI Helmholtz Centre for Heavy Ion Research Darmstadt 

In a recent article published in "Physical Review Letters", L. Nies et al. report on measurements of the isomeric excitation energies in neutron-deficient indium isotopes. The experiment was performed using the ISOLTRAP  multireflection time-of-flight mass spectrometer (MR-TOF MS) at ISOLDE /CERN, Geneva. The high precision measurements exploited a major improvement in the resolution of the ISOLTRAP MR-TOF MS. This allowed to measure the excitation energy (671(37) keV) of the 1/2⁻ isomer in ⁹⁹In at N=50 for the first time.
The systematics of the isomer excitation energy now reach the crucial N=50 shell closure, confirming its constancy, even when all neutrons are removed from the valence shell.

Advances in modern nuclear models are not only of interest for nuclear shell structure investigations but are also frequently used in metrology, atomic physics, and quantum chemistry.
The improved experimental results were compared to state-of-the-art large-scale shell model (LSSM) and density functional theory (DFT) calculations, as well as to ab initio calculations using the valence-space in-medium similarity renormalization group (VS-ISMRG) and the CCSM method. The models have difficulties describing both the isomer excitation energies and ground-state electromagnetic moments along the indium chain.

Please read more in the article ... >

Further information also in the press release of CERN .

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.

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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 .