Resolution of Chiral Conundrum in ${}^{106}\mathrm{Ag}$: Doppler-Shift Lifetime Investigation

The nature of the chiral candidate bands in ${}^{106}\mathrm{Ag}$, one of only two known examples of candidates which actually cross, is investigated experimentally and theoretically. Lifetimes have been determined for these bands in ${}^{106}\mathrm{Ag}$ using the Doppler-shift attenuation method with the $\gamma$-detector array AFRODITE. The level scheme of ${}^{106}\mathrm{Ag}$ has been extended, and three negative-parity bands have been observed to high spins. Configurations were assigned to the negative-parity bands based on a quasiparticle alignment analysis and on configuration-fixed constrained relativistic mean field calculations. The excitation energies, $B(M1)$ and $B(E2)$ values, as well as $B(M1)/B(E2)$ ratios have been compared with results of particle-rotor model calculations. From the investigations, it is concluded that the three close-lying negative-parity bands are a two-quasiparticle high-$K$ band and a pair of four-quasiparticle bands. The proposal that the two lowest-lying bands are chiral partners has not been confirmed.

Figure 1

Partial level scheme of ${}^{106}\mathrm{Ag}$. The widths of the arrows represent the relative intensities of the transitions. The lifetimes in ps, deduced in the present work, are indicated; their uncertainties are, on average, 20%.

Figure 2

The line-shape analysis of the 966.6 keV $\gamma$ line deexciting the ${16}^{-}$ level of band 2 in ${}^{106}\mathrm{Ag}$ is shown for (a) the 45° spectrum (forward direction) and (b) the 135° spectrum (backward direction).

Figure 3

Comparison of experimental (symbols) and calculated (lines) excitation energies and electromagnetic transition properties of (a) band 1 and (b) bands 2 and 3. The open squares for band 1 indicate results from Ref. [23]. The theoretical results for $\pi g_{9/2}^{-1}\otimes \nu \{g_{7/2}{\}}^2\nu h_{11/2}$ configurations of bands 2 and 3 are displayed as dashed and dotted lines, respectively. The $B(M1)$ values of bands 2 and 3 are also compared with calculations using a $\pi g_{9/2}^{-1}\otimes \nu h_{11/2}^3$ configuration, shown as dash-dot-dotted and dash-dotted lines, respectively.

Figure 4

Quasiparticle alignment $i$ as function of rotational frequency for (a) band 1 and (b) bands 2 and 3 in ${}^{106}\mathrm{Ag}$. The experimental points are shown as full symbols. The alignments deduced from the neighboring nuclei are indicated as straight lines. Results of theoretical calculations are displayed as dashed and dotted lines. The Harris parameters used are ${\mathcal{J}}_0=8.9{\hslash }^2/\mathrm{MeV}$ and ${\mathcal{J}}_1=15.7{\hslash }^4/{\mathrm{MeV}}^3$ [39].