Low-lying isomeric states in ${}^{80}\mathrm{Ga}$ from the ${\beta }^{-}$ decay of ${}^{80}\mathrm{Zn}$

A new level scheme of ${}^{80}\mathrm{Ga}$ has been determined. This nucleus was populated following the ${\beta }^{-}$ decay of ${}^{80}\mathrm{Zn}$ at ISOLDE, CERN. The proposed level scheme is significantly different compared to the previously reported one and contains 26 levels up to 3.4 MeV in excitation energy. The present study establishes that the previously identified 1.9-s ${\beta }^{-}$-decaying $6^{-}$ isomer is the ground state of ${}^{80}\mathrm{Ga}$ and the 1.3-s ${\beta }^{-}$-decaying 3${}^{-}$ isomer lies at an excitation energy of 22.4 keV. A new isomeric level was identified at 707.8 keV and its half-life was measured to be 18.3(5) ns, allowing the 685.4-keV transition de-exciting this state to be assigned an $M2$ multipolarity. The newly measured spectroscopic observables are compared with shell-model calculations using the jj44bpn and JUN45 interactions.

Figure 1

Level scheme of ${}^{80}\mathrm{Ga}$ populated in the $\beta$ decay of ${}^{80}\mathrm{Zn}$. There are a total of 86 $\gamma$ transitions. The dotted lines indicate weak transitions. The transition labels show the energy value and the relative $\gamma$ intensity. For absolute intensity per 100 decays, multiply by 0.41(6). $I_{\beta }$ values were determined by an intensity balance between the $\gamma$ rays feeding and de-exciting each level. The log$ft$ values were calculated using $Q_{\beta }=$ 7290 keV from [21]. Half-lives for the 6${}^{-}$ and 3${}^{-}$ states are taken from [4].

Figure 2

HPGe $\gamma \text{−}\gamma$ coincidence spectra containing transitions from ${}^{80}\mathrm{Ga}$ with gates on the relevant 403-, 174-, 637-, and 1151-keV transitions.

Figure 3

(a) 742.0-keV gate from $\gamma \text{−}\gamma$ HPGe coincidence spectra. (b) 742.0-keV gate on HPGe in the $\beta \text{−}{\gamma }_{\mathrm{HPGe}}\text{−}{\gamma }_{{\mathrm{LaBr}}_3\text{(Ce)}}$ spectra. The time was recorded with time-to-amplitude converters between the plastic scintillator ($\beta$ detector) and each LaBr${}_3$(Ce) detector. The time spectra have an offset of 6 ns. (c) Delayed ($T>8$ ns) $\beta \text{−}$gated spectra in LaBr${}_3$(Ce).

Figure 4

Comparison of the experimental levels (left) and shell-model calculations. The experimental level scheme is the same as the one presented in Fig. 1. The model space used for both interactions was $p_{3/2}{f}_{5/2}{p}_{1/2}{g}_{9/2}$. The region from 0 to 600 keV contains all the predicted levels. Due to high level density, the region from 600 to 1800 keV contains only the predicted levels with $J\le 3$ and $J^{\pi }=7_1^{-}$. The $>1800$-keV region contains only the levels with $J^{\pi }=1^{+}$.