Sr90 emits 1MeV beta. Very very bad if you ingest it but easy to protect yourself if you're near it. The Cs137 is a lot harder to be around. And we don't want

Sr90 emits 1MeV beta. Very very bad if you ingest it but easy to protect yourself if you're near it. The Cs137 is a lot harder to be around. And we don't want either in the water or food chain.