High-spin structures in ${}^{132}\mathrm{Xe}$ and ${}^{133}\mathrm{Xe}$ and evidence for isomers along the $N=79$ isotones

The transitional nuclei ${}^{132}\mathrm{Xe}$ and ${}^{133}\mathrm{Xe}$ are investigated after multinucleon-transfer (MNT) and fusion-evaporation reactions. Both nuclei are populated (i) in ${}^{136}\mathrm{Xe}+{}^{208}\mathrm{Pb}$ MNT reactions employing the high-resolution Advanced GAmma Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA, (ii) in the ${}^{136}\mathrm{Xe}+{}^{198}\mathrm{Pt}$ MNT reaction employing the GAMMASPHERE spectrometer in combination with the gas-detector array CHICO, and (iii) as an evaporation residue after a ${}^{130}\mathrm{Te}(\alpha ,xn){}^{134-xn}\mathrm{Xe}$ fusion-evaporation reaction employing the HORUS $\gamma$-ray array at the University of Cologne. The high-spin level schemes are considerably extended above the $J^{\pi }=\left(7^{-}\right)$ and $\left({10}^{+}\right)$ isomers in ${}^{132}\mathrm{Xe}$ and above the $11/2^{-}$ isomer in ${}^{133}\mathrm{Xe}$. The results are compared to the high-spin systematics of the $Z=54$ as well as the $N=78$ and $N=79$ chains. Furthermore, evidence is found for a long-lived ($T_{1/2}\gg 1\mu \mathrm{s}$) isomer in ${}^{133}\mathrm{Xe}$ which closes a gap along the $N=79$ isotones. Shell-model calculations employing the SN100PN and PQM130 effective interactions reproduce the experimental findings and provide guidance to the interpretation of the observed high-spin features.

Figure 1

Comparison of high-spin states and isomer half-lives along the $N=79$ isotones ranging from ${}^{129}\mathrm{Sn}$ to ${}^{139}\mathrm{Nd}$; data are taken from Refs. [13, 25, 28, 29, 30, 32, 38, 39, 40]. Tentative assignments are written in parentheses. See text for details.

Figure 2

Correlation of two coincident $\gamma$ rays between excited states of spin $J_i$. The transitions are further characterized by their multipole-mixing ratios ${\delta }_i$ (adapted from Ref. [58]).

Figure 3

Partial level scheme of ${}^{132}\mathrm{Xe}$ with the newly observed $\gamma$ rays above the 8.39(11)-ms $\left({10}_1^{+}\right)$ and 87-ns $\left(7_1^{-}\right)$ isomers. Energies are given in keV. Intensities above the isomers are extracted from the in-beam ${}^{136}\mathrm{Xe}+{}^{208}\mathrm{Pb}$ AGATA data and normalized to the intensity of the 650-keV transition.

Figure 4

Partial level scheme of ${}^{133}\mathrm{Xe}$. Energies are given in keV. Intensities above the isomers are extracted from the in-beam ${}^{136}\mathrm{Xe}+{}^{208}\mathrm{Pb}$ AGATA data and normalized to the intensity of the 695-keV transition.

Figure 5

Left: AGATA $\gamma$-ray spectra for ${}^{132}\mathrm{Xe}$ identified with PRISMA after the ${}^{136}\mathrm{Xe}+{}^{208}\mathrm{Pb}$ MNT reaction. (a) Gate on small TKEL. (b) Gate on large TKEL; the transitions below the long-lived $\left({10}_1^{+}\right)$ and $\left(7_1^{-}\right)$ isomers are not present any more. The applied gates on the TKEL distributions are presented in the insets (c) and (d). Previously unknown $\gamma$ rays are labeled with italic characters. Right, (e)–(g): Prompt GAMMASPHERE $\gamma \gamma$ coincidences from the ${}^{136}\mathrm{Xe}+{}^{198}\mathrm{Pt}$ experiment, gated on 650, 1133, and 1240 keV. (h) Delayed-prompt GAMMASPHERE coincidence spectrum with a gate on the delayed 668-keV $2_1^{+}\to 0_1^{+}$ transition. Asterisks mark transitions not observed in the HORUS and AGATA experiments. See text for details.

Figure 6

AGATA $\gamma$-ray spectra of ${}^{133}\mathrm{Xe}$ selected by PRISMA with gates on (a) small TKEL and (b) large TKEL; corresponding TKEL spectra in (c) and (d) with gates marked in black. Previously unknown $\gamma$-ray transitions are labeled with italic characters. Arrows label the supposed positions of the 231- and 247-keV $\gamma$-ray transitions. (e)–(g) GAMMASPHERE prompt $\gamma \gamma$ coincidences with gates on 948, 1253, and 468 keV. (h), (j), (k) HORUS prompt $\gamma \gamma$ coincidences with gates on 695, 948, and 1160 keV. Contaminations originating from the dominating $2n$ evaporation channel ${}^{132}\mathrm{Xe}$ are labeled with filled black circles.

Figure 7

(a) $\gamma \gamma$ angular correlations for the $5_1^{+}\stackrel{\delta }{\to }{4}_1^{+}\stackrel{E2}{\to }{2}_1^{+}$ 727-773-keV cascade in ${}^{132}\mathrm{Xe}$. Experimental values (data points) are compared to calculated angular-correlation functions $W({\theta }_1,{\theta }_2,\varphi )$ (lines) for six correlation groups $({\theta }_1,{\theta }_2,\varphi )$ using the code corleone. The known multipole-mixing ratio of the 727-keV transition in ${}^{132}\mathrm{Xe}$ is well reproduced by the corleone calculation. (b) Same as (a), but for the 247-948-keV cascade in ${}^{133}\mathrm{Xe}$. Several spin hypotheses are plotted. The $19/2\stackrel{\delta }{\to }19/2^{-}\stackrel{}{\to }15/2^{-}$ hypothesis (solid line) with $\delta =-0.69\left(11\right)$ yields the best agreement.

Figure 8

Comparison of experimental energy spectra with the results of shell-model calculations for (a) ${}^{132}\mathrm{Xe}$ and (b) ${}^{133}\mathrm{Xe}$. Experimental energy spectra are shown in the left panels. The middle panels present the results obtained with the PQM130 interaction [4]. The right panels show the computed levels using the SN100PN interaction. For clarity, the states are separated into columns for the negative- and the positive-parity states.

Figure 9

Evolution of excited states (a) along the $N=78$ isotones from $Z=50$ to $Z=64$, (b) along the Xe isotopes, and (c) along the odd-mass $N=79$ isotones. Data are from Refs. [40, 69, 70, 71]. Newly discovered states are marked with thick lines.

Figure 10

Decomposition of the total angular momentum $I=I_{\pi }\otimes I_{\nu }$ of the SN100PN calculation into its proton and neutron components for several selected negative-parity states as well as the $J^{\pi }=23/2^{+}$ isomer candidate in (a) to (f) ${}^{131}\mathrm{Te}$ and (g) to (l) ${}^{133}\mathrm{Xe}$. Strongest components are labeled with corresponding percentages.