Intel's Ronler Acres Plant

Silicon Forest

Saturday, November 28, 2009

Velocity, Part 3

I was just thinking about alpha particles again. My last theory was that as they went zooming by neutral atoms, if they passed close enough, the electrons that surrounded the atom would be attracted to the alpha particle, and vice versa, and this pull, this force, would exert some drag on the alpha particle and cause it to slow down some small amount. After a few million of these interactions, enough force would have been applied to the alpha particle to bring it to rest.

I was also thinking that if an alpha particle managed to snag an electron, it wouldn't slow it down much because the mass of an electron is so tiny compared to the mass of an alpha particle. If the alpha particle did pick up an electron it would just charge on it's merry way.

There were two things I neglected:
  1. The force required to break the electron free from it's previous nucleus, and
  2. once the alpha particle acquires an electron, it is no longer a particle, it is now an atom, with all the honors and responsibilities that go with that title.
So it could be just that on it's travels, the alpha particle comes close enough to an atom, not just enough to feel the attraction of the electrons, but to actually snag one. The force required to break the electron free from it's previous host may be enough to cut the alpha particle's velocity by a considerable amount. Of course on a single interaction like this, any momentum lost by the alpha particle will be added to the atom that is losing the electron. How much velocity is added to the donating atom will be inversely proportional to it's mass. Oxygen and Nitrogen molecules weigh 7 to 9 times what a alpha particle weighs, so the velocity they will acquire will be a fraction of the alpha particle's velocity.

Even if this snagging operation does not slow down our errant particle, it is now an atom, so instead of being able to blithely zoom through the electron clouds of other atoms, it is now going to be repelled by them. It's like there was one kid's balloon per acre to watch out for, now there's a blimp every acre. They are going to be a little harder to miss. And every time you run into one, some of your energy (velocity) is going to be transferred to the target (blimp, atom) and you will rebound with slightly less energy (velocity).


Ole Phat Stu said...

See Compton Scattering.

Charles Pergiel said...

Compton Scattering? Good grief! The more you look at this stuff, the more complex it becomes. I liked the good old days, back when there were only protons, electrons and neutrons. Hmm, guess there never was such a time, except in my 6th grade mind.