[ko_kyi]

IIRC, uranium mostly emits alpha particles, which would hardly penetrate a couple feet of water. (Any actual scientists care to comment/correct?)

[RadioAstronomer]

Look at post 174 :-)

[Robert A Cook PE]

Alpha's can't even penetrate the dead skin cell's on your hand. (The alpha particle hits the dead skin cells, the energy gets absorbed in the layer of dead cells, and nothing happens. The cells are already dead.) In other words, you can hold a handful of alpha-emitting material in your hand, and not get irradiated by the alpha particles.

(However: each time an apha particle is created by radioactive decay, some gamma rays are also emitted. Gamma energy varies from very little, to medium, to high. Depends on the isotope. The alpha particles can't touch you, but the gamma's that are also coming out of the material will penetrate your hand. Of course, if they penetrate your hand, they have come out the other side, and so they haven't hurt either!)

BUT - Big BUT - if an alpho-emitting piece of material (even something smaller than a grain of pollen!) gets in the air, then you "might" breathe it in if you are not wearing a dust mask.

IF you breathe in these little particles, THEN, when they decay, ALL of the energy is deposited in the very small area around the very small particle inside your lungs or bones. THAT deposits a lot of energy in the living cells close to the particle, which DOES lead to cancer.