Excitation ofSem77,Brm79, andIrm191byCs137γ rays

Abstract
Excitation of the 17.4 s Sem77, 4.9 s Brm79, and 4.9 s Irm191 isomers by γ rays of a strong Cs137 source was observed for the first time. Using a 67 TBq (1800 Ci) source for irradiation, isomeric activities were measured by means of γ spectrometry. Identifying principal activation levels, photoexcitation cross sections were determined, allowing level lifetimes to be deduced.