Reevaluation of the Ne22(α,γ)Mg26 and Ne22(α,n)Mg25 reaction rates

Philip Adsley, Umberto Battino, Andreas Best, Antonio Caciolli, Alessandra Guglielmetti, Gianluca Imbriani, Heshani Jayatissa, Marco La Cognata, Livio Lamia, Eliana Masha, Cristian Massimi, Sara Palmerini, Ashley Tattersall, and Raphael Hirschi
Phys. Rev. C 103, 015805 – Published 19 January 2021

Abstract

Background: The competing Ne22(α,γ)Mg26 and Ne22(α,n)Mg25 reactions control the production of neutrons for the weak s process in massive and asymptotic giant branch (AGB) stars. In both systems, the ratio between the corresponding reaction rates strongly impacts the total neutron budget and strongly influences the final nucleosynthesis. A number of experimental studies have been performed over recent years which necessitate the reevaluation of the Ne22(α,γ)Mg26 and Ne22(α,n)Mg25 reaction rates. Evaluations of the reaction rates following the collection of new nuclear data presently show differences of up to a factor of 500, resulting in considerable uncertainty in the resulting nucleosynthesis.

Purpose: To reevaluate the Ne22(α,γ)Mg26 and Ne22(α,n)Mg25 reaction rates using updated nuclear data from a number of sources including updating spin and parity assignments.

Methods: With updated spin and parity assignments, the levels which can contribute to the reaction rates are identified. The reaction rates are computed using a Monte Carlo method which has been used for previous evaluations of the reaction rates in order to focus solely on the changes due to modified nuclear data.

Results: The evaluated Ne22(α,γ)Mg26 reaction rate remains substantially similar to that of Longland et al. but, including recent results from Texas A&M, the Ne22(α,n)Mg25 reaction rate is lower at a range of astrophysically important temperatures. Stellar models computed with newton and mesa predict decreased production of the weak branch s process due to the decreased efficiency of Ne22 as a neutron source. Using the new reaction rates in the mesa model results in Zr96/Zr94 and Ba135/Ba136 ratios in much better agreement with the measured ratios from presolar SiC grains.

Conclusion: The Ne22+α reaction rates Ne22(α,γ)Mg26 and Ne22(α.n)Mg25 have been recalculated based on more recent nuclear data. The Ne22(α,γ)Mg26 reaction rate remains substantially unchanged since the previous evaluation but the Ne22(α.n)Mg25 reaction rate is substantially decreased due to updated nuclear data. This results in significant changes to the nucleosynthesis in the weak branch of the s process.

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  • Received 14 October 2019
  • Revised 13 April 2020
  • Accepted 2 November 2020

DOI:https://doi.org/10.1103/PhysRevC.103.015805

©2021 American Physical Society

Physics Subject Headings (PhySH)

Nuclear Physics

Authors & Affiliations

Philip Adsley1,2,3,*, Umberto Battino4,†, Andreas Best5,6, Antonio Caciolli7,8, Alessandra Guglielmetti9, Gianluca Imbriani5,6, Heshani Jayatissa10, Marco La Cognata11, Livio Lamia12,11,13, Eliana Masha9, Cristian Massimi14,15, Sara Palmerini16,17, Ashley Tattersall4,†, and Raphael Hirschi18,19,†

  • 1Institut Physique Nucléaire d'Orsay, UMR8608, CNRS-IN2P3, Universite Paris Sud 11, 91406 Orsay, France
  • 2iThemba Laboratory for Accelerator Based Sciences, Somerset West 7129, South Africa
  • 3School of Physics, University of the Witwatersrand, Johannesburg 2050, South Africa
  • 4School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3FD, United Kingdom
  • 5University of Naples “Federico II” Corso Umberto I 40, 80138 Napoli NA, Italy
  • 6Istituto Nazionale di Fisica Nucleare, Sezione di Napoli, Strada Comunale Cinthia, 80126 Napoli NA, Italy
  • 7Dipartimento di Fisica e Astronomia, Università degli Studi di Padova, Via F. Marzolo 8, 35131 Padova, Italy
  • 8Istituto Nazionale di Fisica Nucleare, Sezione di Padova, Via F. Marzolo 8, 35131 Padova, Italy
  • 9Università degli Studi di Milano and INFN Milano, Via Celoria 16, 20133 Milano, Italy
  • 10Physics Division, Argonne National Laboratory, Argonne, Illinois 60439, USA
  • 11Laboratori Nazionali del Sud - Istituto Nazionale di Fisica Nucleare, Via Santa Sofia 62, 95123 Catania, Italy
  • 12Università degli Studi di Catania, Dipartimento di Fisica e Astronomia “E. Majorana”, via Santa Sofia 64, Italy
  • 13CSFNSM-Centro Siciliano di Fisica Nucleare e Struttura della Materia, Via Santa Sofia 64, 95123 Catania, Italy
  • 14Istituto Nazionale di Fisica Nucleare, Sezione di Bologna, Bologna, Italy
  • 15Dipartimento di Fisica e Astronomia, Università di Bologna, Bologna, Italy
  • 16Dipartimento di Fisica e Geologia, Università degli Studi di Perugia, Perugia, Italy
  • 17Istituto Nazionale di Fisica Nucleare, Sezione di Perugia, Perugia, Italy
  • 18School of Chemical and Physical Sciences, Keele University, Keele ST5 5BG, United Kingdom
  • 19Kavli IPMU (WPI), University of Tokyo, Kashiwa 277-8583, Japan

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Vol. 103, Iss. 1 — January 2021

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