well it wasn't the Alpha particle that was spiraling it was the vapor cause by the Alpha particle shooting along a piece of black thick paper which was soaked in alcohol and then frozen by dry ice, the Alpha particle didn't seem to be effected too much by the magnet, the way I could tell was because the line of vapor went on a in a strait line even after passing the magnet, there was only a bend in the line caused from the pull of the magnetic field pulling on the vapor, and the vapor trail always resumed the strait line it was on before reaching the magnet, if there was a pull on the Alpha particle the magnetic field was too weak to cause vary much change in the particles direction and I was not able to see it with my naked eye.
I got the Alpha particles and cloud chamber together in a science kit from a place called Edmond Scientific, but the web site is www.scientificsonline.com there is also another place called The Chem Shop where you can get a bunch of Chemical stuff, its worth checking out if you don't already have a place to get all the Chems you would like
and also I think that the reason the vapor was more easily manipulated by the magnetic field is because the vapor has complete atoms which obviously have electrons which are as we know easily manipulated by magnetic fields, and from what I can understand would give any matter a stronger chance of being manipulated by a magnetic field as opposed to a Alpha particle which doesn't have any electrons