hi, Im looking to build a Geiger counter
and I need advice as to whether my design is sound.
for the tube: im going to make a capacitor inside a film can filled with butane or another
gas whose conductance is varied by alpha, beta,
or gamma radiation. this will be hooked to an interrupter whose clicks will correspond with the background radiation.

also, any ideas for other gasses?

Question: How do you intend to test this?

I have an alpha/beta emitter, Americium 241
and my town is near old Uranium mines.
and I have a couple real counters

try searching http://www.howstuffworks.com for ideas

Also, www.wikipedia.com

Hmmm...a Geiger counter works by counting the amount of ions made by radiation, so you would have to find a way to do that. As for the gas, i believe that Argon is used in Geigers.