Proton superfluidity and charge radii in proton-rich calcium isotopes

Abstract

One of the most important global properties of the atomic nucleus is its size. Experimentally determined nuclear charge radii carry unique information on the nuclear force and complex dynamics of protons and neutrons moving inside the nucleus. The intricate behaviour of charge radii along the chain of Ca isotopes, including the unexpectedly large charge radius of neutron-rich 52Ca, poses a daunting challenge for nuclear theory1. Here we present the measurements of the charge radii of proton-rich isotopes 36,37,38Ca, whose properties are impacted by the interplay between nuclear superfluidity and weak binding. Calculations carried out within nuclear density functional theory show that the combination of a novel interaction2 and a state-of-the-art theoretical method can successfully explain the behaviour of charge radii from the lightest to the heaviest Ca isotopes. Through this model, we show how the new data on 36,37,38Ca elucidate the nature of nucleonic pairing in weakly bound proton-rich isotopes.

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Fig. 1: Experimental set-up and hyperfine spectra.
Fig. 2: Charge radii of Ca isotopes.
Fig. 3: Single-proton structure.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.

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Acknowledgements

This work was supported in part by the National Science Foundation, Grant No. PHY-15-65546; the US Department of Energy, National Nuclear Security Administration, Grant No. DE-NA0002924; the US Department of Energy, Office of Science, Office of Nuclear Physics, Grant Nos. DE-SC0013365, DE-SC0018083 and DE-AC05-00OR22725 with UT-Battelle, LLC; the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – Projektnummer 279384907 – SFB 1245; and the German Federal Ministry of Education and Research (BMBF), Grant No. 05P12RFFTG.

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A.J.M., K.M., A.K., D.G., J.D.L., Y.L., P.F.M., S.V.P., D.M.R., F.S., C.S. and A.T. performed the experiment. A.J.M., C.K., B.M., W. Nörtershäuser and J.W. designed and installed the upgraded photon detection system. A.J.M. performed data analysis and discussed with K.M., A.K., W. Nörtershäuser and D.M.R. W. Nazarewicz and P.-G.R. performed theoretical analysis. A.J.M., K.M., W. Nazarewicz and P.-G.R. prepared the figures. A.J.M., K.M., W. Nazarewicz and P.-G.R. prepared the manuscript. All authors discussed the results and contributed to the manuscript at all stages.

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Correspondence to K. Minamisono.

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Miller, A.J., Minamisono, K., Klose, A. et al. Proton superfluidity and charge radii in proton-rich calcium isotopes. Nat. Phys. 15, 432–436 (2019). https://doi.org/10.1038/s41567-019-0416-9

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