Sub-threshold states in Ne19 relevant to F18(p,α)O15

J. E. Riley et al.
Phys. Rev. C 103, 015807 – Published 28 January 2021

Abstract

Background: Classical novae result from thermonuclear explosions producing several γ-ray emitters which are prime targets for satellites observing in the MeV range. The early 511keV γ-ray emission depends critically on the F18(p,α)O15 reaction rate which, despite many experimental and theoretical efforts, still remains uncertain.

Purpose: One of the main uncertainties in the F18(p,α)O15 reaction rate is the contribution in the Gamow window of interference between sub-threshold Ne19 states and known broad states at higher energies. Therefore the goal of this work is to clarify the existence and the nature of these sub-threshold states.

Methods: States in the Ne19 compound nucleus were studied at the Tandem-ALTO facility using the F19(He3,t)Ne19 charge-exchange reaction. Tritons were detected with an Enge Split-pole spectrometer while decaying protons or α particles from unbound Ne19 states were collected, in coincidence, with a double-sided silicon strip detector array. Angular correlations were extracted and constraints on the spin and parity of decaying states established.

Results: The coincidence yield at Ex=6.29MeV was observed to be high spin, supporting the conclusion that it is indeed a doublet consisting of high-spin and low-spin components. Evidence for a broad, low-spin state was observed around 6 MeV. Branching ratios were extracted for several states above the proton threshold and were found to be consistent with the literature. R-matrix calculations show the relative contribution of sub-threshold states to the astrophysically important energy region above the proton threshold.

Conclusions: The levels schemes of Ne19 and F19 are still not sufficiently well known and further studies of the analog assignments are needed. The tentative broad state at 6 MeV may only play a role if the reduced proton width is large.

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  • Received 28 July 2020
  • Accepted 27 October 2020

DOI:https://doi.org/10.1103/PhysRevC.103.015807

©2021 American Physical Society

Physics Subject Headings (PhySH)

Nuclear Physics

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Vol. 103, Iss. 1 — January 2021

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