From my high school physics class I remember that there are some particles which exhibit pure alpha decay (i.e. alpha decay to there stable isotope), like Po-210, Po-211 and Bi-209.
What I also know is that alpha particles, due to their low speed, will be absorbed already within a few cell layers of skin ($\sim 40 \mu$m if I remember correctly).
My question comes from the combination of these two points: if you where able to isolate e.g. Bi-209 in a pure form, would it be harmful to swallow it or will all alpha particles be captured in upper tissue layers, thus leaving you fairly unharmed?!
Note: I am asking in particular about particles with pure alpha decay, because if the decay product is a gamma or beta emitter you will probably be harmed by the decay products anyway.