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

Excited states in ¹³⁹Te were observed for the first time, using EUROGAM2 multidetector array to measure prompt-γ radiation following the spontaneous fission of ²⁴⁸Cm. 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 ¹³⁹Te. The 271.0 keV level most likely corresponds to the νh_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 ¹³⁷Sn nucleus are made based on the extended systematics obtained for the N=87 isotones.