Hindered Gamow-Teller Decay to the Odd-Odd $N=Z$ ${}^{62}\mathrm{Ga}$: Absence of Proton-Neutron $T=0$ Condensate in $A=62$

Search for a new kind of superfluidity built on collective proton-neutron pairs with aligned spin is performed studying the Gamow-Teller decay of the $T=1$, $J^{\pi }=0^{+}$ ground state of ${}^{62}\mathrm{Ge}$ into excited states of the odd-odd $N=Z$ nucleus ${}^{62}\mathrm{Ga}$. The experiment is performed at GSI Helmholtzzentrum für Shwerionenforshung with the ${}^{62}\mathrm{Ge}$ ions selected by the fragment separator and implanted in a stack of Si-strip detectors, surrounded by the RISING Ge array. A half-life of $T_{1/2}=82.9(14)\mathrm{ms}$ is measured for the ${}^{62}\mathrm{Ge}$ ground state. Six excited states of ${}^{62}\mathrm{Ga}$, populated below 2.5 MeV through Gamow-Teller transitions, are identified. Individual Gamow-Teller transition strengths agree well with theoretical predictions of the interacting shell model and the quasiparticle random phase approximation. The absence of any sizable low-lying Gamow-Teller strength in the reported beta-decay experiment supports the hypothesis of a negligible role of coherent $T=0$ proton-neutron correlations in ${}^{62}\mathrm{Ga}$.

Figure 1

Activity spectrum of ${}^{62}\mathrm{Ge}$ $\beta$ decay detected in coincidence with the $\beta$ decay of the ${}^{62}\mathrm{Ga}$ daughter nucleus.

Figure 2

${}^{62}\mathrm{Ga}$ $\gamma$-ray spectrum observed in the $\beta$ decay of ${}^{62}\mathrm{Ge}$. Vertical labels mark the energies of peaks assigned to decays of $1^{+}$ states of ${}^{62}\mathrm{Ga}$ populated by GT transitions.

Figure 3

${}^{62}\mathrm{Ga}$ level scheme observed in the ${}^{62}\mathrm{Ge}$ $\beta$ decay built under the assumption that the populated ($1^{+}$) states will deexcite preferentially to the ground state. The excitation energies of the levels are in keV. The log $ft$ values are indicated in the right side of the levels in bold characters.

Figure 4

Experimental (black) and calculated (red) single level $B(\text{GT})$ and accumulated $B(\text{GT})$ values for the ${}^{62}\mathrm{Ge}$ to ${}^{62}\mathrm{Ga}$ $\beta$ decay. Left panels use the ISM approach using the KB3G interaction and right panels use the QRPA approach using the SLy4 interaction. Experimental uncertainty corridors are indicated in gray.