Rick, Cs-137 beta decays to a metastable state of Ba, Ba-137m with a branching ratio of 94.6%. Subsequently, Ba-137m gives off the 662 photon with a 89.9% branching ratio. I suspect that the decay schemes show the "95%" decay to the Ba-137m. The total 662 kev photon from Cs-137 would be 0.946 x 0.899 = 85% -- Roger Sit Stanford Linear Accelerator Center rsithp@slac.stanford.edu