# Harmlessness of a pure alpha decay particle

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.

• I do not think that your question has a simple answer. Harmlessness and penetration, I presume in the human body, have to be defined on where the radiation impinges and how it got in the organism. In the lungs for example, even a first cell layer might increase the probability of cancer. There must exist studies. I have not seen a health physicist answering here, who would be the only one qualified to give an answer to this. have a look at en.wikipedia.org/wiki/Alpha_decay#Toxicity – anna v May 27 '13 at 5:52
• I concur with anna v. Physics tells you the particles won't penetrate far (they won't even go very far in air in most cases). But it is up to biologists to say whether there are any surface tissues that could be problematic if mutated. Certainly most epithelial cells are expected to take the brunt of environmental exposure, but perhaps there are sensitive regions. – user10851 May 27 '13 at 5:56
• "or will all alpha particles be captured in upper tissue layers..." The key here is that the internal organs, unlike the skin, are not protected by a layer of dead cells. They don't have an "upper tissue layer." – user4552 May 27 '13 at 15:43
• @BenCrowell that's a very good point. I never realized that! – Michiel May 27 '13 at 17:01
• Let me put it to you this way: the lethal dose of Po-210 if ingested is a invisibly small speck. Luckily I had it in a liquid solution, but none-the-less I took greater precautions in handling that stuff than in any other operation in my life to date. If you had a spill how would you know when you had it adequately cleaned up??? This is the kind of reason for not eating, drinking, smoking or picking you nose in the laboratory. Develop good lab habits. – dmckee --- ex-moderator kitten May 27 '13 at 17:16