Re: Cloud Chamber

[bkolb@arinc.com]

David Bromwich writes:
>I saw something in a physics journal 10 (or was it 20 ) years ago
>describing a simple cloud chamber for demonstrating the range of
>alpha particles in air.  I think it used methanol and dry ice,    
>producing a supersaturated methanol atmosphere.  I intend to use the
>amerecium source from a smoke detector, to make the source feel
>familiar to my students.

There is an inexpensive kit (under $30US) made by The Science
Source in New England and available from the Fisher Scientific Educational
catalog.  It consists of a flat plastic jar, a styrofoam block, a 0.1 uCi
Pb-210 source and instructions (total value other than the source is less
than a dollar).  You supply the dry-ice and alcohol.  You place a piece of
blotting paper in the plastic jar (actually a plastic cylinder about 5cm
tall), soak it with alcohol, and put the lid on.  Place the jar on dry-ice,
which in turn, is resting on the styrofoam block.  Just at the moment when
a mist start to form in the jar, remove it from the dry-ice -- otherwise
you get freezing and have to start over with fresh alcohol.  This takes a
little practice.  It's at that point you will be able to get alpha and beta
tracks in the mist.  Put the jar back on the dry-ice and repeat.  I don't
think you will have good luck with an Americium source due to the high
emission rate and the inability to deionize this type of chamber quickly.
You are better off with a very weak source.

Good luck.

bill
bkolb@arinc.com