Identification of high-spin proton configurations in Ba136 and Ba137

Abstract

The high-spin structures of 136Ba and 137Ba are investigated after multinucleon-transfer (MNT) and fusion-evaporation reactions. 136Ba is populated in a 136Xe+238U MNT 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 two 9Be + 130Te fusion-evaporation reactions using the High-efficiency Observatory for -Ray Unique Spectroscopy (HORUS) at the FN tandem accelerator of the University of Cologne, Germany. Furthermore, both isotopes are populated in an elusive reaction channel in the 11B+130Te fusion-evaporation reaction utilizing the HORUS -ray array. The level scheme above the J� = 10+ isomer in 136Ba is revised and extended up to an excitation energy of approx. 5.5 MeV. From the results of angular-correlation measurements, the Ex = 3707- and Ex = 4920-keV states are identified as the bandheads of positive- and negative-parity cascades. While the high-spin regimes of both 132Te and 134Xe are characterized by high-energy 12+ ! 10+ transitions, the 136Ba E2 ground-state band is interrupted by negativeparity states only a few hundred keV above the J� = 10+ isomer. Furthermore, spins are established for several hitherto unassigned high-spin states in 137Ba. The new results close a gap along the highspin structure of N < 82 Ba isotopes. Experimental results are compared to large-scale shell-model calculations employing the GCN50:82, Realistic SM, PQM130 and SN100PN interactions. The calculations suggest that the bandheads of the positive-parity bands in both isotopes are predominantly of proton character.