One of my son's is a nuclear physicist who works at a World renowned nuclear facility here in the U.K, I have a Canon FD mm f2 Thorium lens and asked him to research if it was safe, he told me the level of radiation it emits is very small and a fraction of that that workers in the nuclear industry are allowed to absorb annually, he also said that it wasn't much more than that emitted by bananas, or Brazil nuts, however he did say he didn't recommend that I sleep with it under my pillow.