High-$K$, two-quasiparticle states in ${}^{160}\mathrm{Gd}$

Excited states in ${}^{160}\mathrm{Gd}$ were populated via $\beta$ decay from the low- and high-spin isomers in ${}^{160}\mathrm{Eu}$. The high-spin, $K^{\pi }=5^{-}$ state feeds several two-quasiparticle levels, as well as a sequence associated with a $\gamma$ vibration and a $K^{\pi }=4^{+}$, hexadecapole vibrational structure. The decay scheme was significantly improved with the observation of new transitions and states when compared with the two competing level schemes from over four decades ago. Configuration assignments for some of the multiquasiparticle levels have been suggested, based upon decay properties, systematics from neighboring nuclei, and comparisons with theoretical calculations. In addition, 15 new low-spin states and approximately 60 new transitions were observed resulting from the decay of the low-spin ${}^{160}\mathrm{Eu}$ isomer.

Figure 1

Partial level scheme of ${}^{160}\mathrm{Gd}$ resulting from states populated by the high-$K$ isomer in ${}^{160}\mathrm{Eu}$.

Figure 2

(a) Spectrum of all $\beta$-gated transitions falling within the range of 50 s following tape movement to the end of the cycle. The peaks denoted with an asterisk result from a contaminant nuclei in the $A=160$ beam. (b) Summed spectrum resulting from coincidence events with the 491.1- and 560.8-keV $\gamma$ rays. (c) Summed spectrum for coincidence with the 1149.1- and 1214.5-keV transitions.

Figure 3

Comparison between excitation energies for one-quasiproton states calculated using the procedure described in the text and the experimentally observed orbitals ([413]5/2, [532]5/2, [411]3/2, [523]7/2, [420]1/2) in ${}^{159}\mathrm{Eu}$ [25], [541]3/2 in ${}^{155}\mathrm{Eu}$ [26], and ([541]1/2, [404]7/2, [402]5/2, and [411]1/2) in ${}^{161}\mathrm{Tb}$ [27] (labeled as Experiment in the figure). The positive/negative energies indicate states above/below the Fermi level, respectively.

Figure 4

Comparison between excitation energies for one-quasineutron states calculated using the procedure described in the text, and the experimentally observed levels in ${}^{161}\mathrm{Gd}$ [25] with the [521]1/2 and [633]7/2 orbitals from ${}^{171}\mathrm{Yb}$ [28] (labeled as Experiment in the figure). The positive/negative energies indicate states above/below the Fermi level, respectively.

Figure 5

Excitation energy of the $K^{\pi }=4^{+}$ states of possible hexadecapole vibration states in gadolinium and dysprosium nuclei. Note that both $K^{\pi }=4^{+}$ states in ${}^{160}\mathrm{Gd}$ are shown in the figure.