Isomers and high-spin structures in the N = 81 isotones Xe 135 and Ba 137

Le résumé fourni par la source

The high-spin structures and isomers of the $N=81$ isotones $^{135}\mathrm{Xe}$ and $^{137}\mathrm{Ba}$ are investigated after multinucleon-transfer (MNT) and fusion-evaporation reactions. Both nuclei are populated (i) in $^{136}\mathrm{Xe}+^{238}\mathrm{U}$ and (ii) $^{136}\mathrm{Xe}+^{208}\mathrm{Pb}$ MNT reactions employing the high-resolution Advanced Gamma Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA, (iii) in the $^{136}\mathrm{Xe}+^{198}\mathrm{Pt}$ MNT reaction employing the $\ensuremath{\gamma}$-ray array GAMMASPHERE in combination with the gas-detector array CHICO, and (iv) via a $^{11}\mathrm{B}+^{130}\mathrm{Te}$ fusion-evaporation reaction with the HORUS $\ensuremath{\gamma}$-ray array at the University of Cologne. The high-spin level schemesof $^{135}\mathrm{Xe}$ and $^{137}\mathrm{Ba}$ are considerably extended to higher energies. The 2058-keV $(19/{2}^{\ensuremath{-}})$ state in $^{135}\mathrm{Xe}$ is identified as an isomer, closing a gap in the systematics along the $N=81$ isotones. Its half-life is measured to be 9.0(9) ns, corresponding to a reduced transition probability of $B(E2,19/{2}^{\ensuremath{-}}\ensuremath{\rightarrow}15/{2}^{\ensuremath{-}})=0.52(6)$ W.u. The experimentally deduced reduced transition probabilities of the isomeric states are compared to shell-model predictions. Latest shell-model calculations reproduce the experimental findings generally well and provide guidance to the interpretation of the new levels.

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