# Key $^{19}$Ne states identified affecting $\gamma$-ray emission from $^{18}$F in novae

## TL;DR

This study identifies key $^{19}$Ne nuclear states affecting $^{18}$F gamma-ray emission in novae, refining reaction rates and reducing uncertainties in nova gamma-ray detection predictions.

## Contribution

First measurement of $^{19}$Ne states relevant to $^{18}$F destruction, providing more accurate reaction rates for nova models.

## Key findings

- Identification of two long-sought $^{19}$Ne levels.
- Reduction of reaction rate uncertainty by a factor of 1.5-17.
- Decreased uncertainty in nova gamma-ray detection probability.

## Abstract

Detection of nuclear-decay $\gamma$ rays provides a sensitive thermometer of nova nucleosynthesis. The most intense $\gamma$-ray flux is thought to be annihilation radiation from the $\beta^+$ decay of $^{18}$F, which is destroyed prior to decay by the $^{18}$F($p$,$\alpha$)$^{15}$O reaction. Estimates of $^{18}$F production had been uncertain, however, because key near-threshold levels in the compound nucleus, $^{19}$Ne, had yet to be identified. This Letter reports the first measurement of the $^{19}$F($^{3}$He,$t\gamma$)$^{19}$Ne reaction, in which the placement of two long-sought 3/2$^+$ levels is suggested via triton-$\gamma$-$\gamma$ coincidences. The precise determination of their resonance energies reduces the upper limit of the rate by a factor of $1.5-17$ at nova temperatures and reduces the average uncertainty on the nova detection probability by a factor of 2.1.