Influence of the $np$ interaction on the $\beta$ decay of ${}^{94}$Pd

We present results from stopped beam rare isotope spectroscopic investigations at the GSI (RISING) experiment based on the detection of $\gamma$-ray transitions following the $\beta$ decay of ${}^{94}$Pd. A comparison between the measured low-lying level scheme of ${}^{94}$Rh and the prediction from shell-model calculations reveals the important roles of the $g_{7/2}$ and $g_{9/2}$ orbitals in explaining the structural features. The low values of the Gamow-Teller strengths $B\left(GT\right)$ can be attributed to the influence of the neutron-proton interaction, which gives rise to an increased seniority mixing for the nuclear states, thereby leading to a fragmentation of the strength to several daughter levels. These results provide further strong indications that ${}^{94}$Pd resides in the middle of a structural transition region in the Pd isotopes as the $N=Z$ line is approached.

Figure 1

$\gamma$-ray spectra associated with the decay of (a) the ${}^{94}$Pd nuclei, where symbols are used to mark the 822, 846, and 896 (*) and 863 keV (+) lines and (b) all of the nuclei implanted in the active DSSSD. The majority of the lines can be associated with the known decays of nuclei as indicated [35]. New as well as the known $\gamma$ transitions in ${}^{94}$Rh are marked in red (light). Unidentified peaks are marked in black (dark) only with their energies. (c) The correlation efficiencies CE (multiplied by 1000) deduced from the spectra in (a) and (b). (d) Implantations per strip in the active DSSSD (i.e., hit distributions) corresponding to several $\gamma$ rays are also shown. See the text for details.

Figure 2

Deduced (EXP) and calculated (GF, FPG, GF-GD) level schemes for ${}^{94}$Rh. Levels up to 4 MeV relevant for the ${\beta }^{+}/EC$ decay are shown. The lowest two states in EXP correspond to ${}^{94m1}$Rh and ${}^{94m3}$Rh. See the text for details.