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Unfolding of exotic near-threshold structure and decay dynamics in B17

A. Volya1,*, S. M. Wang (王思敏)2,3,†, M. Płoszajczak4,‡, and Z. C. Xu (许志成)2,3,§

  • *Contact author: avolya@fsu.edu
  • †Contact author: wangsimin@fudan.edu.cn
  • ‡Contact author: marek.ploszajczak@ganil.fr
  • §Contact author: xuzhicheng@fudan.edu.cn
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Phys. Rev. Research 8, 013125 – Published 4 February, 2026

DOI: https://doi.org/10.1103/1mt3-jbf1

Abstract

Neutron-rich boron isotopes provide a valuable testing ground for threshold-driven structure and reaction phenomena, including halo formation and exotic decay modes. In particular, the structure of B17 and its relation to unbound B16 are of special interest. The B16 nucleus is slightly unbound by approximately 50 keV, while B17 is bound with a neutron separation energy of about 1.4–1.6 MeV. The observation of a 1640 keV γ ray in B17, which we argue originates from a 1/2− excited state, points to a remarkable situation in which γ decay and two-neutron decay can compete. We analyze and identify the main reasons for the competition: L=2 emission of the neutron pair and structural realignment driven by the proximity of the one-body threshold, in particular the nearby s-wave neutron decay channel. The decay is a unique near-threshold L=2 process in which multiple structural components contribute, each with coexisting direct and virtual sequential amplitudes whose interference governs the observables. Because threshold dynamics, continuum coupling, and interference of multiple quantum pathways are universal, closely related scenarios arise in ultracold atoms near Feshbach resonances, few-body atomic and molecular breakups, mesoscopic and photonic open systems, and other areas where open-quantum-system effects impact observables. We employ advanced theoretical models to study this first-of-its-kind case and provide a coherent theoretical perspective based on configuration interaction and complex-energy formalisms that incorporate both reaction continuum and structural effects near threshold.

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Phys. Rev. Research 8, 013125– Published 4 February, 2026
  • Received 16 October 2025
  • Accepted 9 January 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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