Velocity

I've been studying up on Americium. It's one of those artificial transuranic elements, like Plutonium. Normally I don't pay much attention to the elements that come after Plutonium in the periodic table as they are mostly laboratory curiosities: some scientist detected evidence of the existence of one atom for one fraction of a nanosecond. Not much of real practical value there. Americium is another story. It gets used in the smoke detectors you find in houses all over the country. There are probably a hundred million of them, and more getting churned out every minute.

I probably still wouldn't care, but my friend Jack had a smoke detector die the other day, so being the kind of guy he is, he took it apart, just to see what it's made of. So that stirred my interest in Americium.

Americium is element 95, right after Plutonium in the periodic table. Starting with Uranium, we have Uranium (Element 92), Neptunium, Plutonium and then Americium. Each of these elements comes in a number of different Isotopes, each of which has varying degrees of stability and emits different amounts and kinds of radiation. Americium 241 is what gets used in smoke detectors and it gives off the least hazardous kind of radiation: Alpha particles. These are the weak little particles that can be stopped by a sheet of paper. Still, you don't want to be eating any Americium. Alpha particles have an electrical charge and that kind of thing can disturb chemical reactions, which is what your body runs on. Once upon a time the Soviets poisoned a guy with Polonium. Polonium's big danger is that it also gives off Alpha particles.

So, besides eating or breathing an Alpha-emitter, what makes it so not dangerous? Alpha particles aren't all that big. They are composed of four baryons (two neutrons and two protons) bound closely together. They are essentially the nucleus of a Helium atom, that is, a Helium atom with the electrons stripped off.

Neutron radiation on the other hand is extremely dangerous. Now why the big difference? I mean neutrons are a little smaller than alpha particles. It's like comparing an orange to a melon, but not like comparing an orange to the planet Earth. Neutrons don't carry a charge, and Alpha particles do, but there generally aren't any charged particles lying about. So I don't see as that either of these is going to make much difference. But Alpha particles are stopped by a sheet of paper, and neutrons can go through several feet of concrete. I'm going to step out on a limb here and say it is because of their velocity. I suspect Alpha particles have a velocity that can be conveniently measured feet per second, while neutron velocities are in the range of miles per second.