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

The high-spin structures and isomers of the N = 81 isotones ¹³⁵Xe and ¹³⁷Ba are investigated after multinucleon-transfer (MNT) and fusion-evaporation reactions. Both nuclei are populated (i) in ¹³⁶Xe+²³⁸U and (ii) ¹³⁶Xe+²⁰⁸Pb MNT reactions employing the high-resolution Advanced Gamma Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA, (iii) in the ¹³⁶Xe+¹⁹⁸Pt MNT reaction employing the γ-ray array GAMMASPHERE in combination with the gas-detector array CHICO, and (iv) via a ¹¹B+¹³⁰Te fusion-evaporation reaction with the HORUS γ-ray array at the University of Cologne. The high-spin level schemes of ¹³⁵Xe and ¹³⁷Ba are considerably extended to higher energies. The 2058-keV (19/2−) state in ¹³⁵Xe 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⁻ → 15/2⁻) = 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.