$20\hspace{0.5em}\mu s$ isomeric state in doubly odd ${}_{61}^{134}\mathrm{Pm}$

Recoil-isomer tagging at the Accelerator Laboratory of the University of Jyväskylä has been used to establish the isomeric nature of a known ($7^{-}$) excited state in the doubly odd nucleus ${}^{134}\mathrm{Pm}$. The isomeric state was determined to have a half-life of 20(1) $\mu s$ and was populated from the decay of a $\pi h_{11/2}\otimes \nu h_{11/2}$ band using the ${}^{92}\mathrm{Mo}({}^{54}\mathrm{Fe},2\alpha 3\mathit{pn})$ reaction at 305 and 315 MeV. The isomer decays by a 71-keV transition that provides an intermediate step in linking the established ${}^{134}\mathrm{Pm}$ high-spin level scheme to the lower-spin states observed from the $\beta$ decay of ${}^{134}\mathrm{Sm}$. Electron-conversion analysis for the 71-keV $\gamma$-ray transition reveals that it is of $E1$ character and its small reduced-transition probability suggests that ${}^{134}\mathrm{Pm}$ may have a nuclear shape more rigid than that of the neighboring nuclei.

Figure 1

Recoil-isomer-tagged spectra from a prompt-delayed matrix where the delayed $\gamma$ rays were detected $1\text{−}60\hspace{0.5em}\mu$s after a recoil passed through the first MWPC. (a) Planar spectrum showing the new 71-keV delayed transition from a single gate on the known prompt 272-keV transition in ${}^{134}\mathrm{Pm}$. The 38.6- and 43.9-keV peaks are the $K_{\alpha }$ and $K_{\beta }$ x rays of Pm, respectively. The low-energy tailing in this spectrum results from incomplete charge collection on the planar $X$ strips. (b) JUROGAM spectrum showing prompt transitions from the $\pi h_{11/2}\otimes \nu h_{11/2}$ band in ${}^{134}\mathrm{Pm}$ from a single gate on the delayed 71-keV $\gamma$ ray in ${}^{134}\mathrm{Pm}$. All labeled peaks have been assigned to ${}^{134}\mathrm{Pm}$.

Figure 2

Partial level scheme for ${}^{134}\mathrm{Pm}$ showing the newly assigned 20(1) $\mu s$ isomeric state and the new 71-keV $E1$ decay transition. The prompt transitions above the ($7^{-}$) state were established in Ref. [20]. The lower-spin $(2^{+})$ and $(5^{+})$ states are from $\beta$-decay and fusion-evaporation measurements, respectively; however, the ordering of these states is uncertain [21, 22]. Several transitions are known to feed the $(2^{+})$ state populated from the $\beta$ decay of ${}^{134}\mathrm{Sm}$; however, no transitions have been established to feed the $(5^{+})$ state [21, 22].

Figure 3

Time spectrum for the new 71-keV delayed $\gamma$-ray transition in ${}^{134}\mathrm{Pm}$. The solid line represents the sum of two fitted exponentials, with the longer-lived component representing the effect of random correlations (see text for details). The “TIME” axis label refers to the time difference between a recoil passing through the first MWPC and the detection of the delayed $\gamma$ ray.