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Masses of exotic calcium isotopes pin down nuclear forces

An Erratum to this article was published on 28 August 2013

This article has been updated


The properties of exotic nuclei on the verge of existence play a fundamental part in our understanding of nuclear interactions1. Exceedingly neutron-rich nuclei become sensitive to new aspects of nuclear forces2. Calcium, with its doubly magic isotopes 40Ca and 48Ca, is an ideal test for nuclear shell evolution, from the valley of stability to the limits of existence. With a closed proton shell, the calcium isotopes mark the frontier for calculations with three-nucleon forces from chiral effective field theory3,4,5,6. Whereas predictions for the masses of 51Ca and 52Ca have been validated by direct measurements4, it is an open question as to how nuclear masses evolve for heavier calcium isotopes. Here we report the mass determination of the exotic calcium isotopes 53Ca and 54Ca, using the multi-reflection time-of-flight mass spectrometer7 of ISOLTRAP at CERN. The measured masses unambiguously establish a prominent shell closure at neutron number N = 32, in excellent agreement with our theoretical calculations. These results increase our understanding of neutron-rich matter and pin down the subtle components of nuclear forces that are at the forefront of theoretical developments constrained by quantum chromodynamics8.

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Figure 1: Experimental set-up.
Figure 2: Time-of-flight spectra.
Figure 3: Comparison of experimental results with theoretical predictions.

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This work was supported by the BMBF (contracts 06GF9102, 05P12HGCI1, 05P12HGFNE, 06DA70471, 06DD9054), the DFG (grants SFB 634 and GE2183/2-1), the ERC (grant 307986 STRONGINT), the EU through ENSAR (grant 262010), the Helmholtz Alliance HA216/EMMI, the French IN2P3, the ISOLDE Collaboration and the Max-Planck Society. Computations were performed at the Jülich Supercomputing Center.

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D.B., Ch.B., R.B.C., S.K., D.L., V.M., D.N., M.R., J. Stanja, F.W. and R.N.W. performed the experiment. V.M. and F.W. performed the data analysis. J.D.H., J.M., A.S. and J. Simonis performed the NN+3N (MBPT) calculations. K.B., S.K., D.L., A.S., L.S. and F.W. prepared the manuscript. All authors discussed the results and contributed to the manuscript at all stages.

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Correspondence to F. Wienholtz.

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The authors declare no competing financial interests.

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Wienholtz, F., Beck, D., Blaum, K. et al. Masses of exotic calcium isotopes pin down nuclear forces. Nature 498, 346–349 (2013).

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