Quote Originally Posted by Worker 11811 View Post
Thorium only emits alpha particles. Right?
Yes and no. The most abundant isotope 232Th decays mainly by alpha emmision but also by spontaneous fission and very rarely emission of two beta particles. The daughter isotopes must also be considered. The principal isotope of thorium decays as follows;

232Th -> 228Ra -> 228Ac -> ...

Both of the first two daughters decay by beta emission. There may be a gamma emitter in the chain. If you are interested you may trace the decay chain which ultimately results in a stable lead isotope.