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Precision Mass Measurements Reveal Low Neutron Pairing in Tin beyond N=82 and Its Impact on Stellar Nucleosynthesis

A. Mollaebrahimi1,2,3,*, C. Walls4,2, T. Dickel3,1, T. Miyagi5,6,7,8, A. Sieverding9,10, C. Andreoiu11, J. Ash2, B. Ashrafkhani12,2, I. Belosevic2 et al.

J. Bergman1, C. Brown13, T. Brunner14, J. Cardona4,2, L. Egoriti2, G. Gelinas12,2, G. Gwinner4, Z. Hockenbery14,2, J. D. Holt2,14, A. Jacobs15,2, S. Kakkar4,2, B. Kootte4,2, J. Lassen2, E. M. Lykiardopoulou15,2, S. Malbrunot-Ettenauer2,16, G. Martínez-Pinedo3,5,17, S. F. Paul2, W. R. Plaß3,1, M. P. Reiter13, A. Ridley2, C. Scheidenberger3,1,18, R. I. Thompson12, Y. Wang15,2, M. E. Wieser12, and A. A. Kwiatkowski19,2

  • *Contact author: A.mollaebrahimi@GSI.de
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Phys. Rev. Lett. 134, 232701 – Published 10 June, 2025

DOI: https://doi.org/10.1103/ctyj-ls15

Abstract

We present a study on neutron-rich tin (Z=50) isotopes beyond the doubly closed shell of N=82 through high-precision mass measurements, including the first-ever measurements of the masses of Sn136, Sn137, and Sn138 isotopes. These measurements enhance our understanding of the nuclear structure and astrophysical nucleosynthesis in this previously unexplored region. The new mass data are used for evaluation of the final abundances of mass numbers A=135 and 137 in r-process network calculations. Our findings reveal a notable change in the empirical pairing gap for tin isotopes beyond the N=82 closed shell and a shift in the two-neutron-separation energy slope compared to heavier elements above the shell closure. A new set of ab initio calculations effectively describes these observed trends.

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Phys. Rev. Lett. 134, 232701– Published 10 June, 2025
  • Received 1 August 2024
  • Revised 15 November 2024
  • Accepted 14 May 2025
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