Greentext

So long as you don’t wind up with a piece of the alpha-emitter inside you (ex. by eating it, breathing it, introduction via a wound) they are radiologically harmless. Alpha particles are highly charged and comparatively heavy since they have two protons and two neutrons. That mass and charge means that they make a lot of collisions and dump a ton of energy along a short track… VERY short, like the diameter of an individual cell even. Devastating if they are doing that in living tissue due to massive energy deposition all concentrated in a particular area, but on the outside the layers of your skin will adequately protect you. Or, as memes of old have put it:

They are of more concern as like an airborne gas or dusty contamination since you may not be aware if you are breathing them in or accidentally eating traces after touching a innocuous looking dusty surface and not washing your hands before lunch.

A little thought exercise they tell you when you study radiation: if you were to hypothetically have four equivalent activity sources that emitted alpha, beta, gamma and neutron radiation, and you have only four methods of either putting one in your pocket, throwing it in the trash, eating it, or holding it in your hand, which emitter do you match to which method?

Alpha is fine to hold in your hand since your skin will block the alpha particles; you want to avoid eating it because that would really mess you up. Beta has a bit more penetration so you don’t want to have it in your hand but the pocket is relatively fine. Neutron radiation is very penetrating except for moderators similar in mass to neutrons like the hydrogen atoms in water which the neutrons collide with and dump a ton of energy on; unfortunately you are made up of a lot of excellent moderating material where those neutrons would dump a lot of energy in you so you don’t want those anywhere near you and it’s best to throw that source away. Gammas are also highly penetrating so they don’t care that much about small differences like being in your hand or pocket but through having basically no mass and no charge they aren’t particularly likely to interact with you either so all else being equal they’re the safest of the emitters to have inside you if that’s a forced option.