Lifetime measurements of the negative-parity $7^{-}$ and $8^{-}$ states in ${}^{122}\mathrm{Cd}$

The Advanced Time-Delayed $\beta \gamma \gamma$(t) method was used to measure lifetimes of selected high-spin states in ${}^{122}\mathrm{Cd}$ populated from ${\beta }^{-}$ decay of the $J^{\pi }=(9^{-})$ isomer in ${}^{122}\mathrm{Ag}$. From the $\gamma \gamma$ coincidences, a new energy level was established at 2616.6 keV with a suggested spin-parity assignment of $8^{-}$. Lifetimes were determined for the high-spin states at 2616.6 and 2502.7 keV as $T_{1/2}=1.35(29)$ ns and 0.24(6) ns, respectively. The transition rates for γ rays de-exciting the $7^{-}$ states in the $N=74$ isotones of ${}^{122}\mathrm{Cd}$, ${}^{124}\mathrm{Sn}$, and ${}^{126}\mathrm{Te}$ were found to be very similar.

Figure 1

Level scheme for the mixed β decay of the high- and low-spin isomers of ${}^{122}\mathrm{Ag}$ to ${}^{122}\mathrm{Cd}$ and level half-lives determined in this $\beta \gamma \gamma$ study. The decay scheme is dominated by the high-spin decay. The low-spin decay of ${}^{122}\mathrm{Ag}$ is also present, albeit weakly, as manifested by the weak population of the 1367.4-, 2316.7-, and 2577.8-keV states. Any single transition connecting the β-fed level to the ground state was not observed in this study and thus would be missing from the level scheme. This affects only the low-spin decay of ${}^{122}\mathrm{Ag}$. See text for details.

Figure 2

Partial energy spectra sorted from the triple coincidence $\beta \gamma \gamma$ events. (a and b) Energy spectra in one of the Ge detectors sorted from the β-Ge-Ge data when the 113.9- and 324.7-keV transitions are selected in the other Ge detector, respectively. (c) Energy spectrum recorded in the LaBr${}_3$ detector when the 324.7-keV transition was selected in the Ge detector. Energy spectra shown in the (b) and (c) panels are equivalent and illustrate the difference in the energy resolutions of the Ge and LaBr${}_3$ detectors.

Figure 3

Time-delayed spectra due to the lifetimes of the 2616.6-keV (a) and the 2502.7-keV levels (b); see text for details.

Figure 4

Energy systematics of selected states in the $N=74$ isotones of ${}^{122}\mathrm{Cd}$, ${}^{124}\mathrm{Sn}$, and ${}^{126}\mathrm{Te}$; data from this work and Refs. [15, 16]. The positioning of the levels is according to a linear energy scale. The $M1,E1$, and $E2$ labels mark transitions for which the $B(X\lambda$) values are given in Table .