Measurement of the $2^+\rightarrow 0^+$ ground-state transition in the $\beta$ decay of $^{20}$F

TL;DR

This paper reports the first detection and measurement of a rare second-forbidden beta decay transition in $^{20}$F, providing new data that refines astrophysical models of stellar evolution and electron-capture rates.

Contribution

The study presents the first experimental detection and quantification of the $2^+ ightarrow 0^+$ transition in $^{20}$F decay, supported by shell-model calculations, with implications for astrophysics.

Findings

Branching ratio measured as approximately 4.1 x 10^{-6}

Log ft value determined to be 10.89(11)

Electron-capture rate on $^{20}$Ne constrained within 25%

Abstract

We report the first detection of the second-forbidden, non-unique, $2^+\rightarrow 0^+$, ground-state transition in the $\beta$ decay of $^{20}$F. A low-energy, mass-separated $^{20}\rm{F}^+$ beam produced at the IGISOL facility in Jyv\"askyl\"a, Finland, was implanted in a thin carbon foil and the $\beta$ spectrum measured using a magnetic transporter and a plastic-scintillator detector. The $\beta$-decay branching ratio inferred from the measurement is $b_{\beta} = [ 0.41\pm 0.08\textrm{(stat)}\pm 0.07\textrm{(sys)}] \times 10^{-5}$ corresponding to $\log ft = 10.89(11)$, making this one of the strongest second-forbidden, non-unique $\beta$ transitions ever measured. The experimental result is supported by shell-model calculations and has significant implications for the final evolution of stars that develop degenerate oxygen-neon cores. Using the new experimental data, we argue that the astrophysical electron-capture rate on $^{20}$Ne is now known to within better than 25% at the relevant temperatures and densities.