Millisecond 23/2+ isomers in the N = 79 isotones 133Xe and 135Ba

Detailed information on isomeric states in A ≈ 135 nuclei is exploited to benchmark shell-model calculations in the region northwest of doubly-magic nucleus 132 Sn. The N = 79 isotones 133 Xe and 135 Ba are studied after multinucleon transfer (MNT) in the 136 Xe + 208 Pb reaction employing the high-resolution Advanced GAmma Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA at the Laboratori Nazionali di Legnaro, Italy and in a pulsed-beam experiment at the FN tandem accelerator of the University of Cologne, Germany utilizing a 9 Be+ 130 Te fusion-evaporation reaction at a beam energy of 40 MeV. Isomeric states are identified via delayed γ-ray spectroscopy. Hitherto tentative excitation energy, spin, and parity assignments of the 2107-keV J π = 23/2 + isomer in 133 Xe are confirmed and a half-life of T 1/2 = 8.64(13) ms is measured. The 2388-keV state in 135 Ba is identified as a J π = 23/2 + isomer with a half-life of 1.06(4) ms. The new results show a smooth onset of isomeric J π = 23/2 + states along the N = 79 isotones and close a gap in the high-spin systematics towards the recently investigated J π = 23/2 + isomer in 139 Nd. The resulting systematics of M2 reduced transition probabilities is discussed within the framework of the nuclear shell model. Latest large-scale shell-model calculations employing the SN100PN, GCN50:82, SN100-KTH, and a realistic effective interaction reproduce the experimental findings generally well and give insight into the structure of the isomers.