Yrast excitations in the N = 82 isotone Cs-137 have been identified for the
first time in thick-target gamma-ray coincidence measurements for the syst
em Th-232+Xe-136 using the Gammasphere array. The Cs-137 nuclei were produc
ed in deep inelastic one-proton-transfer reactions. By-products of the main
investigation were two well-developed rotational bands which were identifi
ed in heavy reaction partner products complementary to Cs-137 and are tenta
tively assigned to the little studied nucleus Ac-231. There was no difficul
ty in placing the 11 observed Cs-137 transitions in a yrast level scheme ex
tending to an I-pi = (31/2(-)) level at 5494 keV. Interpretation was also s
traightforward, since the experimental level energies are in close agreemen
t with results of shell model calculations performed earlier using empirica
l single particle energies and interaction matrix elements derived from exp
erimental data for other N = 82 isotones.