Lifetime measurement for the $15/2_1^{-}$ and 13/$2_1^{-}$ levels in ${}^{129}\mathrm{Sn}$

Lifetimes of the $15/2_1^{-}$ and 13/$2_1^{-}$ levels in ${}^{129}\mathrm{Sn}$ have been measured using $\gamma \text{−}\gamma$ fast timing technique which come out to be 10(3) ps and 6(4) ps, respectively. The excited states were populated through internal transition decay of higher lying $\mu \mathrm{s}$ isomers in ${}^{129}\mathrm{Sn}$ produced as fission fragments and mass separated by the Lohengrin separator at Institut Laue-Langevin. The generalized centroid difference method was applied with four ${\mathrm{LaBr}}_3$(Ce) detectors, placed at the focal plane of the separator. The measured lifetimes and absolute transition probabilities are discussed in the light of large scale shell model calculations to interpret the single particle configurations and their mixing.

Figure 1

The IC gated $\gamma \text{−}\gamma$ data are shown for both IC-${\mathrm{LaBr}}_3\text{−}{\mathrm{LaBr}}_3$ and IC- ${\mathrm{LaBr}}_3$-clover coincidences. The observed $\gamma$ peaks are marked for the three different isobars which are being observed. The $\gamma$ rays of ${}^{129}\mathrm{Sn}$ and ${}^{129}\mathrm{Sb}$ come from their IT decays whereas those of ${}^{129}\mathrm{Te}$ are observed due to $\beta$ decay of $\mu \mathrm{s}$ isomer in ${}^{129}\mathrm{Sb}$.

Figure 2

The gated projections from IC gated ${\mathrm{LaBr}}_3\text{−}{\mathrm{LaBr}}_3$ and ${\mathrm{LaBr}}_3$-clover coincidence events, corresponding to the cascades of $15/2_1^{-}$ (a,b) and 13/$2_1^{-}$(c,d) levels in ${}^{129}\mathrm{Sn}$. The overlapped projections of ${\mathrm{LaBr}}_3$ and clover with a gate on ${\mathrm{LaBr}}_3$ show the cleanliness of a particular $\gamma$ energy peak that may be used in subsequent lifetime measurement.

Figure 3

The TAC projections for the lifetime measurements of $15/2_1^{-}$ (a) and $13/2_1^{-}$ (b) levels in ${}^{129}\mathrm{Sn}$. The centroid difference ($\mathrm{\Delta }C$ = $\mathrm{\Delta }{C}_{exp}$ = $\mathrm{\Delta }{C}_{\mathrm{FEP}}$) values are shown along with PRD values for the cascades. Lifetimes are also shown that are deduced following the relation $2\tau =\mathrm{\Delta }{C}_{\mathrm{FEP}}-\mathrm{PRD}$. The FWHM values and the total counts obtained are mentioned for both delayed and antidelayed time difference distributions. See text for details.