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Author(s)
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Wienholtz, F (Greifswald U.) ; Beck, D (Darmstadt, GSI) ; Blaum, K (Heidelberg, Max Planck Inst.) ; Borgmann, Ch (Heidelberg, Max Planck Inst.) ; Breitenfeldt, M (Leuven U.) ; Cakirli, R B (Heidelberg, Max Planck Inst. ; Istanbul U.) ; George, S (Greifswald U.) ; Herfurth, F (Darmstadt, GSI) ; Holt, J D (Darmstadt, Tech. Hochsch. ; Darmstadt, EMMI) ; Kowalska, M (CERN) ; Kreim, S (Heidelberg, Max Planck Inst. ; CERN) ; Lunney, D (CSNSM, Orsay) ; Manea, V (CSNSM, Orsay) ; Menéndez, J (Darmstadt, Tech. Hochsch. ; Darmstadt, EMMI) ; Neidherr, D (Darmstadt, GSI) ; Rosenbusch, M (Greifswald U.) ; Schweikhard, L (Greifswald U.) ; Schwenk, A (Darmstadt, EMMI ; Darmstadt, Tech. Hochsch.) ; Simonis, J (Darmstadt, Tech. Hochsch. ; Darmstadt, EMMI) ; Stanja, J (Dresden, Tech. U.) ; Wolf, R N (Greifswald U.) ; Zuber, K (Dresden, Tech. U.) |
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Abstract
| The properties of exotic nuclei on the verge of existence play a fundamental part in our understanding of nuclear interactions. Exceedingly neutron-rich nuclei become sensitive to new aspects of nuclear forces. Calcium, with its doubly magic isotopes $^{40}$Ca and $^{48}$Ca, 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 theory. Whereas predictions for the masses of $^{51}$Ca and $^{52}$Ca have been validated by direct measurements$^4$, 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 $^{53}$Ca and $^{54}$Ca, using the multi-reflection time-of-flight mass spectrometer 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 chromodynamics. |