Millisecond 23/2+ isomers in the N = 79 isotones 133Xe and 135Ba
2018
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.
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