Oblate deformation in neutron-rich ${}^{118,119}\mathrm{Ag}$

High-spin-level schemes of ${}^{118,119}\mathrm{Ag}$ are established for the first time by analyzing the high statistics $\gamma \text{−}\gamma \text{−}\gamma$ and $\gamma \text{−}\gamma \text{−}\gamma \text{−}\gamma$ coincidence data from the spontaneous fission of ${}^{252}\mathrm{Cf}$ at Gammasphere. Two bands with 12 new levels in ${}^{118}\mathrm{Ag}$ and three bands with 14 new levels in ${}^{119}\mathrm{Ag}$ have been identified. A total Routhian surface calculation and projected shell model calculation have been performed to understand the behavior of these two nuclei. The calculations indicate oblate shape in ${}^{118,119}\mathrm{Ag}$.

Figure 1

Level scheme of ${}^{118}\mathrm{Ag}$ obtained in the current work. All the transitions are newly identified.

Figure 2

Partial $\gamma$ coincidence spectra by (a) double gating on 162.3- and 168.1-keV transition to show the low-energy region, (b) double gating on 162.3- and 168.1-keV transition to show the high-energy region, and (c) double gating on 277.8- and 549.7-keV transition to show a low-energy region. The “c” identifies known contaminant lines.

Figure 3

Level scheme of ${}^{119}\mathrm{Ag}$ obtained in the current work. The 130- and 507-keV transitions were reported in $\beta$-decay work previously [14]. Other transitions are newly identified.

Figure 4

Partial $\gamma$ coincidence spectra by (a) double gating on 130.0 and 689.4 keV and (b) double gating on 130.0 and 507.2 keV. The “c” identifies known contaminant lines.

Figure 5

Partial $\gamma$-coincidence spectra by gating on transitions from ${}^{115–119}\mathrm{Ag}$. Transitions are taken from Refs. [5, 10] and the current work. The ${}^{129,130,131,133}\mathrm{Sb}$ fission partner transitions are indicated with neutron evaporation numbers. Note that the count scale of the high-energy regions of parts (d) and (e) have been changed.

Figure 6

Comparison of energy levels (up to ${15}^{-})$ of yrast negative-parity bands in even-$A$ Ag isotopes of ${}^{104–118}\mathrm{Ag}$. Level energies are normalized to zero for the $9^{-}$ levels. Data are taken from Refs. [4, 5, 28, 29, 30, 31, 32] and the current work.

Figure 7

Comparison of $E\left(I\right)-E(I-1)$ vs $I$ of the negative-parity bands in even-$A$ Ag isotopes of ${}^{104–118}\mathrm{Ag}$.

Figure 8

Calculated total Routhian surface of proton positive-parity signature and neutron negative-parity positive signature for ${}^{118}\mathrm{Ag}$. The contour lines are 300-keV increments. The corresponding rotational frequency and minimums are, top left to right and bottom left to right, $\hslash \omega =0.0$ MeV, ${\beta }_2=0.190,\gamma =-2^{\circ },\hslash \omega =0.1$ MeV, ${\beta }_2=0.203,\gamma =-{65}^{\circ };$ $\hslash \omega =0.2$ MeV, ${\beta }_2=0.203,\gamma =-{65}^{\circ }$; $\hslash \omega =0.3$ MeV, ${\beta }_2=0.206,\gamma =-{65}^{\circ }$; $\hslash \omega =0.4$ MeV, ${\beta }_2=0.193,\gamma =-{62}^{\circ }$; $\hslash \omega =0.5$ MeV, ${\beta }_2=0.098,\gamma =-{60}^{\circ }$. Note in polar coordinate ${\beta }_2$ is always positive and $\gamma$ indicates the prolate and oblate shapes.

Figure 9

Projected shell model calculation of the $7^{-}$ band in ${}^{118}\mathrm{Ag}$, compared with experimental data.

Figure 10

Comparison of energy spacing of the $7/2^{+}$ bands in ${}^{115–119}\mathrm{Ag}$. Level energies are normalized to the $7/2^{+}$ and $9/2^{+}$ states, respectively.

Figure 11

Calculated total Routhian surface of proton positive-parity positive signature for ${}^{119}\mathrm{Ag}$. The contour lines are 300-keV increments. The corresponding rotational frequency and minimums are $\hslash \omega =0.0$ MeV, ${\beta }_2=0.151,\gamma =-{120}^{\circ }$; $\hslash \omega =0.1$ MeV, ${\beta }_2=0.185,\gamma =-{67}^{\circ }$; $\hslash \omega =0.2$ MeV, ${\beta }_2=0.184,\gamma =-{67}^{\circ }$; $\hslash \omega =0.3$ MeV, ${\beta }_2=0.129,\gamma =-{43}^{\circ }$; $\hslash \omega =0.4$ MeV, ${\beta }_2=0.129,\gamma =-{40}^{\circ }$; $\hslash \omega =0.5$ MeV, ${\beta }_2=0.086,\gamma =-{65}^{\circ }$.

Figure 12

Projected shell model calculation of the $7/2^{+}$ band in ${}^{119}\mathrm{Ag}$, compared with experimental data.

Figure 13

Band diagram. The 1-qp bands and 3-qp bands are plotted for ${}^{119}\mathrm{Ag}$.