Excited states in Te-139 and the properties of r-process nuclei with Z similar to 50 and N > 86

Abstract

Excited states in Te-139 were observed for the first time, using EUROGAM2 multidetector array to measure prompt-gamma radiation following the spontaneous fission of Cm-248. The systematic behavior of excitation energies in the N = 87 isotones and the multipolarity measurements suggest spin 7/2(-) for the ground state and 9/2(-) for the 271.0 keV level in Te-139. The 271.0 keV level most likely corresponds to the nu hg(9/2) single-particle excitation. A shape transition from spherical to prolate Te isotopes is observed at the neutron number N = 87, in accord with the Hartree-Fock plus BCS, PES calculations. Predictions for excitations in the Sn-137 nucleus are made based on the extended systematics obtained for the N = 87 isotones.

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