Ground-state and pairing-vibrational bands with equal quadrupole collectivity in ${}^{124}\mathrm{Xe}$

The nuclear structure of ${}^{124}\mathrm{Xe}$ has been investigated via measurements of the ${\beta }^{+}$/EC decay of ${}^{124}\mathrm{Cs}$ with the $8\pi \gamma$-ray spectrometer at the TRIUMF-ISAC facility. The data collected have enabled branching ratio measurements of weak, low-energy transitions from highly excited states, and the $2^{+}\to 0^{+}$ in-band transitions have been observed. Combining these results with those from a previous Coulomb excitation study, $B(E2;2_3^{+}\to 0_2^{+})=78\left(13\right)$ W.u. and $B(E2;2_4^{+}\to 0_3^{+})=53\left(12\right)$ W.u. were determined. The $0_3^{+}$ state, in particular, is interpreted as the main fragment of the proton-pairing vibrational band identified in a previous ${}^{122}\mathrm{Te}$(${}^3\mathrm{He},n$)${}^{124}\mathrm{Xe}$ measurement, and has quadrupole collectivity equal to, within uncertainty, that of the ground-state band.

Figure 1

Systematics of the low-lying $0^{+}$ states in the ${}^{120}\mathrm{Xe}$ − ${}^{130}\mathrm{Xe}$ isotopes. Absolute in-band $B(E2;2^{+}\to 0^{+})$ values are shown, where known [16, 17, 18], in W.u. with uncertainties in parentheses. The possible ranges of values for the $0_3^{+}$ bands in ${}^{124}\mathrm{Xe}$ and ${}^{126}\mathrm{Xe}$ were derived from Coulomb excitation analyses [17, 18] for these unobserved transitions. For ${}^{124–130}\mathrm{Xe}$, the values of the ratio of the (${}^3\mathrm{He},n$) cross section attributed to the $0_3^{+}$ state to that of the ground state are written below the $0_3^{+}$ levels in percentages [15, 19].

Figure 2

Partial level scheme observed in the ${\beta }^{+}$/EC decay of ${}^{124}\mathrm{Cs}$. Levels are labeled with their energies in keV and their $J^{\pi }$ values. The transitions are labeled with their energies in keV, with arrow widths proportional to the observed intensity.

Figure 3

Portion of the $\gamma$-ray coincidence spectrum gated on the 915-keV $0_2^{+}\to 2_1^{+}\gamma$ ray showing the 360-keV $\gamma$ ray from the 1629-keV level. The inset displays an expanded region of the spectrum centered near 350 keV.

Figure 4

Portion of the $\gamma$-ray coincidence spectrum gated on the 1336-keV $0_3^{+}\to 2_1^{+}\gamma$ ray showing the 289-keV $\gamma$ ray from the 1979-keV level. The inset displays an expanded region of the spectrum centered near 290 keV.