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Direct mass measurement of Rh91 and Ru89 and mid-shell trend of the one-proton separation energies for N=Z+1 nuclei

Samuel Ayet San Andrés1,*, Meetika Narang2,3, Gabriella Kripkó-Koncz4,5,6, Zhuang Ge2,7,8, Nived Keeppalli4,2,5, Daler Amanbayev4,2,5, Wolfgang R. Plaß2,4, Timo Dickel2,4, Emma Haettner2 et al. (for the Super-FRS Experiment Collaboration)

Emma Haettner2, Christine Hornung4,2, Nicolas Hubbard2, Anu Kankainen7,8, Debodyuti Kar9,2, Kriti Mahajan4,5, Israel Mardor10,11, Ali Mollaebrahimi4, David J. Morrissey12, Christoph Scheidenberger2,4,5, Makar Simonov4,5, Nazarena Tortorelli13,2, Jianwei Zhao2,14, Jasmiina Ahokas7,8, Alejandro Algora1,15, Faraz Amjad2, Juha Äystö7,8, Soumya Bagchi9, Martin Bajzek2, Sönke Beck2,4, Olga Beliuskina7,8, Julian Bergmann4, Andrey Blazhev16, Jeroen Peter Bormans2,17,5, Ziga Brencic18,19, Volha Charviakova20, Paul Constantin21, Justus Eder2, Tommi Eronen7,8, Martina Feijoo-Fontán22, Hans Geissel2,4,†, Simeon Glöckner2, Pablo Gonzalez Rusell23,22, Magdalena Górska2, Antia Graña-González23, Florian Greiner4, Lizzy Gröf4, Jan Hetzel2, Nasser Kalantar-Nayestanaki3, Annesha Karmakar2, Luke Kilmartin24,2, Ronja Knöbel2, Daria Kostyleva2,4, Natalia Kuzminchuk2, Ivan Mukha2, Tobias Murböck4, Dimitrii Nesterenko7, David Ondreka2, Zygmunt Patyk20, Aaron Pieper4, Stephane Pietri2, Ilkka Pohjalainen7, Rinku Prajapat2,25, Martha Reece2, Moritz Pascal Reiter6, Mikael Reponen7,8, Elena Rocco2, Jose Luis Rodríguez-Sánchez23,22, Pratap Roy26, Suraj Kumar Singh2,4, Peter Spiller2, Jens Stadlmann2, Alexandru State21, Ionut C. Stefanescu27,‡, Yoshiki K. Tanaka2,28, Matjaž Vencelj18, Ville Virtanen7,8, Helmut Weick2, Leonard Welde4, Heinrich Wilsenach11, Kathrin Wimmer2, Jan Wirtz2,17, and Jiajun Yu2,29,† (for the Super-FRS Experiment Collaboration)

  • *Contact author: samuel.ayet@uv.es
  • †Deceased.
  • ‡Present address: Institut für Kernphysik, Technische Universität Darmstadt, 64289 Darmstadt, Germany.
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Phys. Rev. C 114, 034311 – Published 8 September, 2026

DOI: https://doi.org/10.1103/lsp5-qntn

Abstract

Neutron-deficient nuclei in the N≈Z, A≈90 region were produced by fragmentation of a relativistic Ag107 beam at the GSI Helmholtz Centre for Heavy Ion Research (GSI), separated in the fragment separator FRS, slowed down, and thermalized, and high-precision mass measurements were performed employing the multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS) of the FRS Ion Catcher. The masses of Rh91,93,95, Ru89, Tc88, Mo87,88,89, and Nb87,88,89 were determined. The mass of Rh91 was measured for the first time. For Ru89, the measured mass excess deviates by more than ten standard deviations (361 keV) from the previous measurement. A possible misidentification of the measured nuclei, including Ru89, with contaminants was excluded using a newly developed identification technique for MR-TOF-MS measurements. For the other nuclides, the measured masses agree well with previous measurements. The impact of the new masses on the one-proton separation energy (Sp) of the nuclei with constant total isospin projection (Tz) in the island of inversion around N=Z=40 is investigated, and signatures of the deformed shell gap at Z=38 are found. A comparison of the experimental Sp values with the predictions of several mass models shows a general agreement of the trends.

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Phys. Rev. C 114, 034311– Published 8 September, 2026
  • Received 23 April 2026
  • Accepted 31 July 2026
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