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  • Letter
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Evidence for a new nuclear ‘magic number’ from the level structure of 54Ca

Abstract

Atomic nuclei are finite quantum systems composed of two distinct types of fermion—protons and neutrons. In a manner similar to that of electrons orbiting in an atom, protons and neutrons in a nucleus form shell structures. In the case of stable, naturally occurring nuclei, large energy gaps exist between shells that fill completely when the proton or neutron number is equal to 2, 8, 20, 28, 50, 82 or 126 (ref. 1). Away from stability, however, these so-called ‘magic numbers’ are known to evolve in systems with a large imbalance of protons and neutrons. Although some of the standard shell closures can disappear, new ones are known to appear2,3. Studies aiming to identify and understand such behaviour are of major importance in the field of experimental and theoretical nuclear physics. Here we report a spectroscopic study of the neutron-rich nucleus 54Ca (a bound system composed of 20 protons and 34 neutrons) using proton knockout reactions involving fast radioactive projectiles. The results highlight the doubly magic nature of 54Ca and provide direct experimental evidence for the onset of a sizable subshell closure at neutron number 34 in isotopes far from stability.

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Figure 1: Schematic illustration highlighting the attractive interaction between the proton πf7/2 and neutron νf5/2 single-particle orbitals for N = 34 isotones.
Figure 2: Systematics of excited-state energies in even–even Ca isotopes and neighbouring nuclei.
Figure 3: Particle identification plots for radioisotopes.
Figure 4: Doppler-corrected γ-ray energy spectra.

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References

  1. Goeppert Mayer, M. On closed shells in nuclei. II. Phys. Rev. 75, 1969–1970 (1949)

    Article  CAS  ADS  Google Scholar 

  2. Warner, D. Not-so-magic numbers. Nature 430, 517–519 (2004)

    Article  CAS  ADS  Google Scholar 

  3. Janssens, R. V. F. Unexpected doubly magic nucleus. Nature 459, 1069–1070 (2009)

    Article  CAS  ADS  Google Scholar 

  4. Bastin, B. et al. Collapse of the N = 28 shell closure in 42Si. Phys. Rev. Lett. 99, 022503 (2007)

    Article  CAS  ADS  Google Scholar 

  5. Otsuka, T., Suzuki, T., Fujimoto, R., Grawe, H. & Akaishi, Y. Evolution of nuclear shells due to the tensor force. Phys. Rev. Lett. 95, 232502 (2005)

    Article  ADS  Google Scholar 

  6. Huck, A. et al. Beta decay of the new isotopes 52K, 52Ca, and 52Sc; a test of the shell model far from stability. Phys. Rev. C 31, 2226–2237 (1985)

    Article  CAS  ADS  Google Scholar 

  7. Gade, A. et al. Cross-shell excitation in two-proton knockout: structure of 52Ca. Phys. Rev. C 74, 021302(R) (2006)

    Article  ADS  Google Scholar 

  8. Janssens, R. V. F. et al. Structure of 52,54Ti and shell closures in neutron-rich nuclei above 48Ca. Phys. Lett. B 546, 55–62 (2002)

    Article  CAS  ADS  Google Scholar 

  9. Dinca, D.-C. et al. Reduced transition probabilities to the first 2+ state in 52,54,56Ti and development of shell closures at N = 32, 34. Phys. Rev. C 71, 041302(R) (2005)

    Article  ADS  Google Scholar 

  10. Chapman, R., Hinds, S. & MacGregor, A. E. A study of 52Cr, 54Cr and 56Cr by the (t,p) reaction. Nucl. Phys. A 119, 305–324 (1968)

    Article  CAS  ADS  Google Scholar 

  11. Bürger, A. et al. Relativistic Coulomb excitation of neutron-rich 54,56,58Cr: on the pathway of magicity from N = 40 to N = 32. Phys. Lett. B 622, 29–34 (2005)

    Article  ADS  Google Scholar 

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

    Article  CAS  ADS  Google Scholar 

  13. Otsuka, T. et al. Magic numbers in exotic nuclei and spin-isospin properties of the NN interaction. Phys. Rev. Lett. 87, 082502 (2001)

    Article  CAS  ADS  Google Scholar 

  14. Honma, M., Otsuka, T. & Mizusaki, T. Shell-model description of neutron-rich Ca isotopes. RIKEN Accel. Prog. Rep. 41, 32 (2008)

    Google Scholar 

  15. Liddick, S. N. et al. Lowest excitations in 56Ti and the predicted N = 34 shell closure. Phys. Rev. Lett. 92, 072502 (2004)

    Article  CAS  ADS  Google Scholar 

  16. Prisciandaro, J. I. et al. New evidence for a subshell gap at N = 32. Phys. Lett. B 510, 17–23 (2001)

    Article  CAS  ADS  Google Scholar 

  17. Janssens, R. V. F. Elusive magic numbers. Nature 435, 897–898 (2005)

    Article  CAS  ADS  Google Scholar 

  18. Crawford, H. L. et al. β decay and isomeric properties of neutron-rich Ca and Sc isotopes. Phys. Rev. C 82, 014311 (2010)

    Article  ADS  Google Scholar 

  19. Rodríguez, T. R. & Egido, J. L. New beyond-mean-field theories: examination of the potential shell closures at N = 32 or 34. Phys. Rev. Lett. 99, 062501 (2007)

    Article  ADS  Google Scholar 

  20. Rejmund, M. et al. Shell evolution and the N = 34 “magic number”. Phys. Rev. C 76, 021304(R) (2007)

    Article  ADS  Google Scholar 

  21. Coraggio, L., Covello, A., Gargano, A. & Itaco, N. Spectroscopic study of neutron-rich calcium isotopes with a realistic shell-model interaction. Phys. Rev. C 80, 044311 (2009)

    Article  ADS  Google Scholar 

  22. Kaneko, K., Sun, Y., Mizusaki, T. & Hasegawa, M. Shell-model study for neutron-rich sd-shell nuclei. Phys. Rev. C 83, 014320 (2011)

    Article  ADS  Google Scholar 

  23. Holt, J. D., Otsuka, T., Schwenk, A. & Suzuki, T. Three-body forces and shell structure in calcium isotopes. J. Phys. G 39, 085111 (2012)

    Article  ADS  Google Scholar 

  24. Hagen, G., Hjorth-Jensen, M., Jansen, G. R., Machleidt, R. & Papenbrock, T. Evolution of shell structure in neutron-rich calcium isotopes. Phys. Rev. Lett. 109, 032502 (2012)

    Article  CAS  ADS  Google Scholar 

  25. Kubo, T. et al. BigRIPS separator and ZeroDegree spectrometer at RIKEN RI Beam Factory. Prog. Theor. Exp. Phys. 03C003. (2012)

  26. Utsuno, Y. et al. Shell evolution around and beyond N = 28 studied with large-scale shell-model calculations. Prog. Theor. Phys. 196 (suppl.). 304–309 (2012)

    Article  CAS  Google Scholar 

  27. Otsuka, T., Suzuki, T., Holt, J. D., Schwenk, A. & Akaishi, Y. Three-body forces and the limit of oxygen isotopes. Phys. Rev. Lett. 105, 032501 (2010)

    Article  ADS  Google Scholar 

  28. Perrot, F. et al. β-decay studies of neutron-rich K isotopes. Phys. Rev. C 74, 014313 (2006)

    Article  ADS  Google Scholar 

  29. Ohnishi, T. et al. Identification of new isotopes 125Pd and 126Pd produced by in-flight fission of 345 MeV/nucleon 238U: first results from the RIKEN RI Beam Factory. J. Phys. Soc. Jpn 77, 083201 (2008)

    Article  ADS  Google Scholar 

  30. Agostinelli, S. et al. GEANT4—a simulation toolkit. Nucl. Instrum. Methods A 506, 250–303 (2003)

    Article  CAS  ADS  Google Scholar 

Download references

Acknowledgements

We thank the staff of the RIKEN Nishina Center accelerator complex for their contribution to the experiment. This work is part of the CNS-RIKEN joint research project on large-scale nuclear structure calculations.

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Contributions

D.S. performed offline data analyses and GEANT4 simulations, wrote the manuscript and prepared the figures. D.S. and S.T. designed the experiment. N.A., P.D., J.L., K.M., M.M., Y.S., D.S., S.T., R.T. and H.W. were responsible for setting up the γ-ray detector array. D.N. prepared the beamline ionization chambers. N.F. and H. Suzuki tuned the BigRIPS separator and the ZeroDegree spectrometer. H.B. was responsible for the data acquisition system. N.A., P.D., S.G., J.L., K.M., M.M., S.M., Y.S., P.-A.S., D.S., T.S., S.T., R.T., J.J.V.-D., H.W. and K.Y. checked data accumulation online and maintained operation of the experiment. M.H., T.O. and Y.U. performed the shell-model calculations. All authors discussed the results and commented on the manuscript.

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Correspondence to D. Steppenbeck.

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The authors declare no competing financial interests.

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Steppenbeck, D., Takeuchi, S., Aoi, N. et al. Evidence for a new nuclear ‘magic number’ from the level structure of 54Ca. Nature 502, 207–210 (2013). https://doi.org/10.1038/nature12522

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