Alpha particles make up roughly 50 percent of the natural radiation exposure
, mostly emitted by Radon
Though they do not even penetrate a sheet of paper or more than a few centimeters of air, alpha particles are in fact quite a health risk.
The reason is that alpha particles, while not terribly high in energy, pack quite a punch. That is, they are relatively heavy and tend to release their kinetic energy
all at once, thus probably damaging something in biological tissue. Compare this to example beta radiation
, ie electrons, that are scattered a lot and get rid of their energy in more manageable portions. Alpha particles therefore have been assigned a high "quality factor" for the calculation of radiation dosage
s - see the writeup on sievert
Besides, Radon is a gas - that means you can breathe it in.
And suddenly there are lots of delicate pulmonary alveole
s within the few centimeters radius. And Radon is everywhere, it is generated in the Uranium decay chain
. It literally seeps out of rocks and tends to accrue in cellars and the like.
Moral of the story: Do not ingest