$\beta$ decay of the very neutron-deficient ${}^{60}\mathrm{Ge}$ and ${}^{62}\mathrm{Ge}$ nuclei

We report here the results of a study of the $\beta$ decay of the proton-rich Ge isotopes, ${}^{60}\mathrm{Ge}$ and ${}^{62}\mathrm{Ge}$, produced in an experiment at the RIKEN Nishina Center. We have improved our knowledge of the half-lives of ${}^{62}\mathrm{Ge}$ [73.5(1) ms] and ${}^{60}\mathrm{Ge}$ [25.0(3) ms] and its daughter nucleus, ${}^{60}\mathrm{Ga}$ [69.4(2) ms]. We measured individual $\beta$-delayed proton and $\gamma$ emissions and their related branching ratios. Decay schemes and absolute Fermi and Gamow-Teller transition strengths have been determined. The mass excesses of the nuclei under study have been deduced. A total $\beta$-delayed proton-emission branching ratio of 67(3)% has been obtained for ${}^{60}\mathrm{Ge}$. New information has been obtained on the energy levels populated in ${}^{60}\mathrm{Ga}$ and on the ${1/2}^{-}$ excited state in the $\beta p$ daughter ${}^{59}\mathrm{Zn}$. We extracted a ground state–to–ground state feeding of 85.3(3)% for the decay of ${}^{62}\mathrm{Ge}$. Eight new $\gamma$ lines have been added to the deexcitation of levels populated in the ${}^{62}\mathrm{Ga}$ daughter.

Figure 1

$Z$ versus $A/Q$ identification plot for the BigRIPS setting optimized for ${}^{65}\mathrm{Br}$, in which both ${}^{60}\mathrm{Ge}$ and ${}^{62}\mathrm{Ge}$ are implanted. The positions of these nuclei are shown.

Figure 2

(a) Charged-particle energy spectrum for decay events correlated with ${}^{60}\mathrm{Ge}$ implants. The peak due to the detection of $\beta$ particles is seen at low energy and fitted by an exponential function (in green). (b) Fit of the peaks related to the proton emission following the $\beta$ decay of ${}^{60}\mathrm{Ge}$ (in red). Peaks are labeled according to the corresponding excitation energies in the $\beta$ daughter ${}^{60}\mathrm{Ga}$. The peak marked by an asterisk corresponds to the transition from the IAS to the first excited state in ${}^{59}\mathrm{Zn}$ (see text).

Figure 3

Spectrum of the time correlations between each proton decay (WAS3ABi energy $E_p>$ 1 MeV) and all ${}^{60}\mathrm{Ge}$ implants. The dashed blue line is the background (fixed by fitting the backward-correlations part) and the red line is the result of the fit.

Figure 4

$\gamma$-ray energy spectrum for decay events correlated with ${}^{60}\mathrm{Ge}$ implants. The observed $\gamma$ lines belong to different nuclei in the decay chain of ${}^{60}\mathrm{Ge}$. Underlined values indicate $\gamma$ lines which are seen for the first time in the present work (see the text). Known $\gamma$ lines are labeled according to the parent nucleus. (a) The region [400,1100] keV is shown with bins of 4 keV/channel. (b) The region [1250,1800] keV is shown with bins of 4 keV/channel. (c) The region [3000,5000] keV is shown with bins of 8 keV/channel.

Figure 5

$\gamma$-ray energy spectrum for decay events correlated with ${}^{59}\mathrm{Zn}$ implants, showing the $\gamma$ deexcitation in ${}^{59}\mathrm{Cu}$. ${}^{59}\mathrm{Zn}$ is also populated in the $\beta$-delayed proton decay of ${}^{60}\mathrm{Ge}$.

Figure 6

$\gamma$-ray energy spectrum for decay events correlated with ${}^{60}\mathrm{Ga}$ implants, showing the $\gamma$ deexcitation in ${}^{60}\mathrm{Zn}$. The ${}^{60}\mathrm{Ga}$ nucleus is also populated in the $\beta$ decay of ${}^{60}\mathrm{Ge}$.

Figure 7

Fit of the correlation-time spectrum obtained for the $\beta$ decay of ${}^{60}\mathrm{Ga}$ (red line). The fit includes the parent activity (green line practically coincident with the red line), the daughter activity (purple line) and the background (dashed blue line) fixed by fitting the backward-correlations part.

Figure 8

Partial decay scheme of ${}^{60}\mathrm{Ge}$ deduced from the results of the present experiment. Evidence is seen of population of levels in four nuclei in the decay chain of ${}^{60}\mathrm{Ge}$: ${}^{60}\mathrm{Ga}, {}^{60}\mathrm{Zn}, {}^{59}\mathrm{Zn}$, and ${}^{59}\mathrm{Cu}$ (see the text for more details). The observed $\gamma$ transitions are indicated by blue arrows, while green arrows indicate the observed proton emission. The quantities in red are deduced from the present data.

Figure 9

Fit of the correlation-time spectrum obtained for the $\beta$ decay of ${}^{62}\mathrm{Ge}$. The green line indicates the parent activity, the purple line is the daughter activity, the dashed blue line is the background (fixed by fitting the backward-correlations part of the spectrum) and the red line is the sum of all.

Figure 10

Charged-particle energy spectrum for decay events correlated with ${}^{62}\mathrm{Ge}$ implants.

Figure 11

$\gamma$-ray energy spectrum for decay events correlated with ${}^{62}\mathrm{Ge}$ implants. Underlined values indicate $\gamma$ lines which are seen for the first time in the present work. (a) The region [450,2200] keV is shown with bins of 2 keV/channel. (b) The region [2400,3800] keV is shown with bins of 4 keV/channel.

Figure 12

Partial decay scheme of ${}^{62}\mathrm{Ge}$ deduced from the results of the present experiment. The observed $\gamma$ transitions are indicated by blue arrows. The quantities in red are deduced from the present data.