Spectroscopy of $^{19}$Ne for the thermonuclear $^{15}$O($\alpha,\gamma$)$^{19}$Ne and $^{18}$F($p,\alpha$)$^{15}$O reaction rates

TL;DR

This study investigates the nuclear structure of $^{19}$Ne to refine reaction rates critical for modeling astrophysical phenomena like X-ray bursts and novae, revealing new level assignments and emphasizing the need for higher resolution experiments.

Contribution

The paper provides new spin-parity assignments for $^{19}$Ne levels and confirms the existence of a triplet of states, improving the nuclear data used in astrophysical reaction rate calculations.

Findings

Confirmed $J^{ ext{ extpi}}$ for 4.14 and 4.20 MeV levels as $9/2^{-}$ and $7/2^{-}$

Confirmed triplet of states around 6.4 MeV in $^{19}$Ne

Suggested existence of unobserved levels near 6.86 MeV

Abstract

Uncertainties in the thermonuclear rates of the $^{15}$O($\alpha,\gamma$)$^{19}$Ne and $^{18}$F($p,\alpha$)$^{15}$O reactions affect model predictions of light curves from type I X-ray bursts and the amount of the observable radioisotope $^{18}$F produced in classical novae, respectively. To address these uncertainties, we have studied the nuclear structure of $^{19}$Ne over $E_{x} = 4.0 - 5.1$ MeV and $6.1 - 7.3$ MeV using the $^{19}$F($^{3}$He,t)$^{19}$Ne reaction. We find the $J^{\pi}$ values of the 4.14 and 4.20 MeV levels to be consistent with $9/2^{-}$ and $7/2^{-}$ respectively, in contrast to previous assumptions. We confirm the recently observed triplet of states around 6.4 MeV, and find evidence that the state at 6.29 MeV, just below the proton threshold, is either broad or a doublet. Our data also suggest that predicted but yet unobserved levels may exist near the 6.86 MeV state. Higher resolution experiments are urgently needed to further clarify the structure of $^{19}$Ne around the proton threshold before a reliable $^{18}$F($p,\alpha$)$^{15}$O rate for nova models can be determined.