Eur. Phys. J. A (2025) 61: 99
https://doi.org/10.1140/epja/s10050-025-01572-y

Review

The ²²Ne($\alpha$,n)²⁵Mg reaction - state of the art, astrophysics, and perspectives

¹ Department of Physics, University of Naples Federico II, Via Cintia, 80126, Naples, NA, Italy
² Sezione di Napoli, INFN, Via Cintia, 80126, Naples, NA, Italy
³ Department of Physics & Astronomy, Texas A&M University, 578 University Drive, 77843-4242, College Station, USA
⁴ Cyclotron Institute, Texas A&M University, 120 Spence Street, 77843-3366, College Station, USA
⁵ School of Chemical and Physical Sciences, Keele University, Lennard–Jones Laboratories, ST5 5BG, Keele, Staffordshire, UK
⁶ Laboratori Nazionali del Gran Sasso, Istituto Nazionale di Fisica Nucleare, Via G. Acitelli 22, 67100, L’Aquila - Localita Assergi, Italy
⁷ Laboratori Nazionali del Sud, Istituto Nazionale di Fisica Nucleare, Via S. Sofia 62, 95100, Catania, Italy
⁸ Department of Physics and Astronomy, University of Notre Dame, 46556, Notre Dame, IA, USA
⁹ National Nuclear Data Center, Brookhaven National Laboratory, Building 817, 11973-5000, Upton, USA
¹⁰ School of Mathematics and Physics, University of Surrey, GU2 7XH, Guildford, UK
¹¹ Dipartimento di Ingegneria ed Architettura, Università degli Studi di Enna “Kore”, Cittadella universitaria, 94100, Enna, Italy

^a andreas.best@unina.it

Received: 20 December 2024
Accepted: 14 April 2025
Published online: 10 May 2025

Abstract

One of the most important stellar neutron sources is the ²²Ne($\alpha ,n$)²⁵Mg reaction, which gets activated both during the helium intershell burning in asymptotic giant branch stars and in core helium and shell carbon burning in massive stars. The ²²Ne($\alpha ,n$)²⁵Mg reaction serves as the main neutron producer for the weak s-process and provides a short but strong neutron exposure during the helium flash phase of the main s-process, significantly affecting the abundances at the s-process branch points. The cross section needs to be known at very low energies, as close as possible to the neutron threshold at $E_{\alpha }=$ 562 keV (Q = −478 keV), but both direct and indirect measurements have turned out to be very challenging, leading to significant uncertainties. Here we discuss the current status of the reaction, including recent and upcoming measurements, and provide a discussion on the astrophysical implications as well as an outlook into the near future.