$β$-delayed spectroscopy of $^{80}$Ge$_{48}$ and competition between Gamow-Teller and first-forbidden transitions in $^{80g+m}$Ga$_{49}$ $β$ decay

TL;DR

This work conducts a detailed β-delayed γ spectroscopy study of $^{80}$Ge populated via β decays of the two $^{80}$Ga precursors ($^{80g}$Ga and $^{80m}$Ga). Using a hybrid detector setup and Bateman-equation analysis, the authors build decay schemes up to $S_n$, separating feeding from the two precursors and extracting log $ft$ values. They find FF transitions contribute about 48% of the total β intensities, leading to substantial shortening of the precursor half-lives when FF is included, in line with theoretical expectations. The results illuminate the GT–FF competition in this near-$N=50$ region, provide 13 and 14 new $^{80}$Ge states populated from $^{80g}$Ga and $^{80m}$Ga respectively, and establish a framework for assigning spin–parity to observed states via log $ft$ analyses, with angular-correlation measurements suggested for firm $J^{ extpi}$ determinations.

Abstract

The $β$-delayed spectroscopy of $^{80}$Ge has been studied using sources of ground and low-lying isomeric states of $^{80}$Ga. A hybrid $γ$-ray spectrometer was used, composed of high-purity germanium (HPGe) detectors for low-energy $γ$-ray detection, phoswich detectors from the PARIS array for high-energy $γ$ rays and a plastic detector for $β$ tagging. The new decay level schemes are presented, with 13 and 14 states $β$ populated by $^{80g}$Ga and $^{80m}$Ga, respectively, being reported for the first time. We quantitatively compare summed intensities of first-forbidden and previously reported Gamow-Teller $β$ transitions [R. Li et al., \href{https://doi.org/10.1103/PhysRevC.111.034303}{Phys. Rev. C 111, 034303 (2025)}]. The upper-limit fractions of first-forbidden transitions contributing to the decays of $^{80g}$Ga and $^{80m}$Ga are (48.0 $\pm$ 2.7)$\%$ and (47.9 $\pm$ 3.3)$\%$ of the observed total $β$ transition intensities of (78.2 $\pm$ 2.5)$\%$ and (82.2 $\pm$ 3.7)$\%$, respectively. Notably, the half-lives decrease in accordance with the upper limits of (48.0 $\pm$ 6.0)$\%$ [3.67(20) s $\rightarrow$ 1.91(3) s] and (47.9 $\pm$ 7.2)$\%$ [3.01(19) s $\rightarrow$ 1.57(1) s] for $^{80g}$Ga and $^{80m}$Ga, respectively, when including first-forbidden transitions, in contrast to those by Gamow-Teller transitions only.

Figures (7)

• Figure 1: $\beta$-gated $\gamma$ spectra in the range 0 to 6000 keV. The marked lines are attributed to transitions in daughter nuclei: filled circles = $^{80}$Ge; filled squares = $^{79}$Ge; empty squares = $^{80}$As and filled triangles = $^{80}$Se. I and II symbols denote single- and double-escape peaks, respectively. Note that I and II are not sequential.
• Figure 2: Level scheme of $^{80}$Ge up to 4.2 MeV in excitation energy populated following the $\beta$ decay of $^{80g}$Ga. For the sake of clarity, the decay scheme has been split in two sections, with the one for the higher energies plotted in Fig. \ref{['fig6.41']}.
• Figure 3: Level scheme of $^{80}$Ge populated following the $\beta$ decay of $^{80g}$Ga containing the high-lying states between 4.2 and 8 MeV in excitation energy.
• Figure 4: Level scheme of $^{80}$Ge up to 4.4 MeV in excitation energy populated following the $\beta$ decay of $^{80m}$Ga. For the sake of clarity, the decay scheme has been split in two sections, with the one for the higher energies plotted in Fig. \ref{['fig6.43']}.
• Figure 5: Level scheme of $^{80}$Ge populated following the $\beta$ decay of $^{80m}$Ga containing the high-lying states between 4.4 and 8 MeV in excitation energy.