Excited levels in the multishaped ${}^{117}\mathrm{Pd}$ nucleus studied via $\beta$ decay of ${}^{117}\mathrm{Rh}$

Monoisotopic samples of exotic, neutron-rich ${}^{117}\mathrm{Rh}$ nuclei, produced in the proton-induced fission of ${}^{238}\mathrm{U}$ and separated using the IGISOL mass separator coupled to the JYFLTRAP Penning trap, were used to perform $\beta$ and $\gamma$ coincidence spectroscopy of ${}^{117}\mathrm{Pd}$. The spin parity of the ground state of ${}^{117}\mathrm{Pd}$ was determined to be $1/2^{+}$ and the 19.1 ms isomer at 203.2 keV was assigned a spin-parity $7/2^{-}$. The ${}^{117}\mathrm{Rh}$ ${\beta }^{-}$-decay scheme was considerably extended, and various sequences of the levels were interpreted as resulting from the prolate, oblate, and triaxial nuclear shapes. Some of the ${\beta }^{-}$ decays were considered as the allowed Gamow-Teller transitions. The experimental distribution of Gamow-Teller strength is discussed.

Figure 1

Ion counts registered with a MCP detector placed after the Penning trap. The resolved atomic ions from the IGISOL isobaric beam are marked with their element symbols.

Figure 2

The singles, $\beta$- and $\mathrm{Pd}\left(K_{\alpha }X\right)$-gated spectra measured with the LEGe detectors for the monoisotopic samples of ${}^{117}\mathrm{Rh}$ (a)–(c) and monoisotopic samples of ${}^{117}\mathrm{Pd}$ [(d), log. scale]. The peaks are labeled with their energies in keV.

Figure 3

The coincidence spectra for monoisotopic samples of ${}^{117}\mathrm{Rh}$. Energy of a gating $\gamma$ line is shown in the top right corner. The peaks are labeled with their energies in keV and the ones due to backscattering are labeled with an asterisk.

Figure 4

Excitation scheme of ${}^{117}\mathrm{Pd}$ as obtained in this work. We interpret the three groups of levels, marked A, B, and C, as related to prolate, triaxial, and oblate deformation, respectively. The $Q_{\beta }$ in keV was taken from Ref. [35] and the half-life from Ref. [36].

Figure 5

Systematics of selected excited levels in odd-A Rh isotopes. The data are taken from Refs. [12, 39, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51]. Dashed lines are drawn to guide the eye.

Figure 6

Systematics of low-spin, positive-parity excited levels in odd-A Pd isotopes. The data are taken from Refs. [4, 6, 44, 45, 46, 47, 48, 49, 50, 51] and the present work. Dashed lines are drawn to guide the eye.

Figure 7

Systematics of the isomeric states and transitions and other relevant levels in the odd-A Pd isotopes. The hindrance factors of the isomeric transitions are shown in square brackets, the factors for ${}^{117}\mathrm{Pd}$ were calculated using intensities found in this work. The data are taken from Refs. [12, 13, 56], ENSDF and the present work.

Figure 8

Systematics of negative-parity levels in odd-A Mo, Ru, and Pd isotopes. The data are taken from Refs. [46, 47, 48, 49, 50, 51] and the present work. Dashed lines are drawn to guide the eye.

Figure 9

The distributions of $B\left(GT\right)$ decay strength for odd $A=115$ and 117 ground-state decays of rhodium to palladium. The data are taken from Ref. [7] and this work. The half-lives [36], the beta-decay energies in keV [35] and the total $B\left(GT\right)$ strengths observed in this work are shown also.