High-spin structures of ¹³⁶₅₅Cs₈₁

A. Astier, M.-G. Porquet, G. Duchêne, F. Azaiez, D. Curien, I. Deloncle, O. Dorvaux, B. J. P. Gall, M. Houry, R. Lucas, P. C. Srivastava, N. Redon, M. Rousseau, O. Stézowski, and Ch. Theisen

Accepted Thursday Apr 25, 2013

Odd-odd $^{136}$Cs nuclei have been produced in the $^{18}$O + $^{208}$Pb and $^{12}$C + $^{238}$U fusion-fission reactions and their $\gamma$ rays studied with the Euroball array. The high-spin level scheme has been built up to $\sim$4.7~MeV excitation energy and spin $I \sim 16\hbar$ from the triple $\gamma$-ray coincidence data. The configurations of the three structures observed above $\sim$~2 MeV excitation energy are first discussed by analogy with the proton excitations identified in the semi-magic $^{137}$Cs$_{82}$ nucleus, which involve the three high-$j$ orbits lying above the $Z=50$ gap, $\pi g_{7/2}$, $\pi d_{5/2}$ and $\pi h_{11/2}$. This is confirmed by the results of shell-model calculations performed in this work.