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Charge Pickup Reaction Cross Section for Neutron-Rich p-Shell Isotopes at 900A  MeV

J.-C. Zhang1,2, B.-H. Sun1,*, I. Tanihata1,2,†, S. Terashima1, F. Wang1, R. Kanungo3,4, C. Scheidenberger5,6,7, F. Ameil5, J. Atkinson3 et al.

Y. Ayyad8, S. Bagchi9, D. Cortina-Gil8, I. Dillmann5,6, A. Estradé3,5, A. Evdokimov5, F. Farinon5, H. Geissel5,6,‡, G. Guastalla5, R. Janik10,‡, S. Kaur3,11, R. Knöbel5, J. Kurcewicz5, Yu. A. Litvinov5, M. Marta5, M. Mostazo8, I. Mukha5, C. Nociforo5, H. J. Ong2, S. Pietri5, A. Prochazka5, B. Sitar10, P. Strmen10,‡, M. Takechi5, J. Tanaka2, J. Vargas8, H. Weick5, and J. S. Winfield5,‡

  • *Contact author: bhsun@buaa.edu.cn
  • †Contact author: tanihata@rcnp.osaka-u.ac.jp
  • ‡Deceased.
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Phys. Rev. X 15, 031004 – Published 2 July, 2025

DOI: https://doi.org/10.1103/k9tj-jq8s

Abstract

We report charge pickup reaction cross sections for 24 p-shell isotopes, including Li8,9, Be10−12, B10,13−15, C12,14−19, and N14,15,17−22, measured at relativistic energies (approximately 900A  MeV) on both hydrogen and carbon targets. For the first time, we reveal a universal rapid increase in the charge pickup cross sections of unstable projectiles with isospin asymmetry along several isotopic chains. The cross sections can be decoupled into distinct contributions from the mass number and isospin asymmetry of the projectile, highlighting the critical role of the latter, and can be formulated empirically.

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Popular Summary

When atomic nuclei collide at nearly the speed of light, a rare transformation can occur in which a neutron turns into a proton—a process known as charge exchange, historically often termed charge. This reaction, which may be related to beta decay, is poorly understood, especially in highly neutron-rich nuclei like those found in radioactive beams or explosive astrophysical events. In this study, we report a surprising new discovery: The probability of this neutron-to-proton flip grows far more rapidly with neutron number than previously believed.

To investigate this, we carry out an experiment at the GSI accelerator in Germany. We produce 24 light p-shell isotopes, ranging from stable to highly neutron rich, and collide them with carbon and hydrogen targets at energies near 900 MeV per nucleon. By measuring the charge pickup cross sections—the likelihood that a proton is gained eventually—we find an exponential rise in probability as more neutrons are added. For example, from carbon-12 to carbon-19, the charge pickup probability increased nearly 50-fold, far exceeding the earlier estimated factor of 2.5. We develop a new empirical formula that separates the effects of nuclear mass and neutron-proton imbalance, moving beyond the limitations of traditional models.

Our results offer fresh insights into the mechanisms behind high-energy nuclear reactions and help explain puzzling features in nuclear beta decay. They also have practical implications for producing rare isotopes and improving nuclear astrophysics simulations.

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Phys. Rev. X 15, 031004– Published 2 July, 2025
  • Received 20 January 2025
  • Revised 6 May 2025
  • Accepted 16 May 2025
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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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