Intermediate-spin states of ${}^{\mathbf{92}}\mathbf{Zr}$ and a large $B\left(E2\right)$ value between the ${10}_1^{+}$ and $8_1^{+}$ states

This study investigated intermediate-spin states of ${}^{92}\mathrm{Zr}$ via the inverse reaction ${}^9\mathrm{Be}\left({}^{86}\mathrm{Kr},3\mathrm{n}\right){}^{92}\mathrm{Zr}$. Seven transitions were newly observed, and a lifetime was extracted for the ${10}_1^{+}$ state by analysis of Doppler-broadened line shapes of decay $\gamma$ rays. A large $B\left(E2\right)$ value was obtained for the transition from ${10}_1^{+}$ to $8_1^{+}$, and the magnitude was comparable to that for the deformed excited configurations in ${}^{94}\mathrm{Zr}$ that have recently been established. A possible origin for such collectivity is discussed qualitatively based on a phenomenological deformed rotor model. Moreover, a multipletlike structure that fits into the systematics for $N=52$ even-$A$ isotones is revealed for the negative-parity yrast states.

Figure 1

Proposed level scheme of ${}^{92}\mathrm{Zr}$ based on an analysis of the $E_{\gamma }\text{−}{E}_{\gamma }$ matrix. Newly observed transitions are marked with asterisks.

Figure 2

Examples of $\gamma \text{−}\gamma$ coincidence spectra. These spectra were obtained from the $E_{\gamma }\text{−}{E}_{\gamma }$ matrix and provide evidence for the newly observed transitions. Energy values are given above the peaks in units of keV. (a) A spectrum obtained by setting a gate on the 650-keV transition from $\left({12}^{+}\right)$ to ${10}^{+}$. (b) A spectrum obtained by setting a gate on the 1462-keV transition from $6^{+}$ to $4^{+}$. (c) A spectrum obtained by setting a gate on the 893-keV transition from $7^{-}$ to $5^{-}$.

Figure 3

Partial level scheme included in the lifetime analysis. Energies of $\gamma$ transitions are given in keV. Deduced mean life is shown on the right of the ${10}^{+}$ state with statistical uncertainties.

Figure 4

Examples of the line-shape fits for the 988-keV transition at ${47}^{\circ },{90}^{\circ }$, and ${105}^{\circ }$ with respect to the beam direction. Results of the fits to the experimental spectra are shown as thick lines. A contaminant peak at 1014 keV is included.

Figure 5

Systematics of $E_x$ vs $I$ for the positive-parity yrast states up to ${14}^{+}$ of even-even Zr isotopes ranging from $N=50$ to $N=60$. (a) The subshell closed structures ${}^{90,96}\mathrm{Zr}$, (b) the intermediate structures ${}^{92,94,98}\mathrm{Zr}$, and (c) the deformed structure ${}^{100}\mathrm{Zr}$.

Figure 6

Comparison of $E_x$ vs $I$ in ${}^{92}\mathrm{Zr}$ from the experiment with a phenomenological curve for an excited deformed rotor. The phenomenological curve is for an excitation energy of $E_0+1.2\times \mathrm{gsb}$ (ground-state band) of ${}^{100}\mathrm{Zr}$. Here, $E_0$ stands for the excitation energy of the $0_2^{+}$ state. The corresponding data points for the known $0_2^{+}$ and $2_2^{+}$ states in ${}^{92}\mathrm{Zr}$ and ${}^{94}\mathrm{Zr}$ also are included in the figure.

Figure 7

Systematics of $E_x$ vs $I$ for the negative-parity yrast states up to ${11}^{-}$ of even-even Zr isotopes ranging from $N=50$ to $N=60$. (a) The subshell closed structures ${}^{90,96}\mathrm{Zr}$, (b) the intermediate structures ${}^{92,94,98}\mathrm{Zr}$, and (c) the deformed structure ${}^{100}\mathrm{Zr}$.

Figure 8

Systematics of the lowest negative-parity excitations for the Zr isotopes. The $6^{+}$ and $8^{+}$ yrast states also are shown for comparison.

Figure 9

Systematics of the yrast positive- and negative-parity states for the $N=52$ even-$A$ isotones.