Yrast structure of the shell model nucleus ${}^{89}\mathrm{Nb}$

Yrast and near-yrast states in $\text{odd-}A$ ${}^{89}\mathrm{Nb}$ were investigated using the ${}^{65}\mathrm{Cu}({}^{28}\mathrm{Si}$,$2p2n)$ reaction at a beam energy of 105 MeV. The $\gamma \text{-ray}$ coincidence events were recorded with the Indian National Gamma Array spectrometer. About 30 new transitions have been observed extending the level structure of this nucleus up to spin $45/2\hslash$ and excitation energy of 10.5 MeV. Large-scale shell model calculations were performed using the effective interactions JUN45 and jj44b to understand the structure of the observed states. Reasonable agreement between the experimental observation and shell model calculations suggests that no cross-shell excitations are important up to the maximum spin observed in the current experiment.

Figure 1

Experimental $\gamma \text{-ray}$ asymmetry parameter (${\Delta }_{\mathrm{asym}})$ plotted against the angular distribution ratio ($R_{\theta })$ for transitions belonging to ${}^{89}\mathrm{Nb}$ (closed square). The dashed lines parallel to the y axis correspond to the values obtained for known pure stretched dipole and quadrupole transitions in ${}^{86}\mathrm{Zr}$ (closed circle) [13], which are labeled by their energy values in keV

Figure 2

Partial level scheme of ${}^{89}\mathrm{Nb}$. The transitions newly identified in the present work are marked with asterisks.

Figure 3

Representative $\gamma \text{-ray}$ coincidence spectrum showing transitions in positive parity structure 1. The spectrum was created with a double gate on 1638- and 258-keV transitions. The peaks marked with asterisks denote transitions newly identified in the present work.

Figure 4

Representative $\gamma \text{-ray}$ coincidence spectrum showing transitions of structure 2. The spectrum was created with a gate on a list from 258-, 932-, and 1003-keV transitions, and one from a list of 1404-, 438-, 489-, 183-, and 244-keV transitions. The peaks marked with asterisks denote transitions newly identified in the present work. The hash-marked peak is an unresolved doublet.

Figure 5

Double-gated $\gamma \text{-ray}$ coincidence spectrum showing transitions depopulating negative parity states (structures 3 and 4). The spectrum was created with double gate on 216- and 664-keV transitions. The peaks marked with asterisks denote transitions newly identified in the present work. Hash-marked peaks are unresolved doublets.

Figure 6

Systematics of positive parity states in $\text{odd-}A$ $N=48$ isotones ${}^{89}\mathrm{Nb}$, ${}^{91}\mathrm{Tc}$ [7], ${}^{93}\mathrm{Rh}$ [20], and ${}^{95}\mathrm{Ag}$ [25].

Figure 7

Experimental and calculated positive parity states in ${}^{89}\mathrm{Nb}$ .

Figure 8

Experimental and calculated negative parity states in ${}^{89}\mathrm{Nb}$. The experimental data for $I^{\pi }=1/2^{-}$ state was taken from Ref. [32].