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

Detailed information on isomeric states in A≈135 nuclei is exploited to benchmark shell-model calculations in the region northwest of doubly magic nucleus Sn132. The N=79 isotones Xe133 and Ba135 are studied after multinucleon transfer in the Xe136+Pb208 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 Be9+Te130 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 Jπ=23/2+ isomer in Xe133 are confirmed and a half-life of T1/2=8.64(13) ms is measured. The 2388-keV state in Ba135 is identified as a Jπ=23/2+ isomer with a half-life of 1.06(4) ms. The new results show a smooth onset of isomeric Jπ=23/2+ states along the N=79 isotones and close a gap in the high-spin systematics towards the recently investigated Jπ=23/2+ isomer in Nd139. 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.