Re: cloud chambers

["Michael Stabin" <michael.g.stabin@vanderbilt.edu>]

Forwarded message from John Andrews:





In a message dated 7/9/2001 12:47:28 PM Eastern Daylight Time,

laradcon@HOTMAIL.COM writes:



> I would very much like to hear from any radsafers in the Los Alamos

>  area who have experience with cloud chamber demonstrations.  I'm

referring

>  to the alcohol vapor/dry ice/ore source classroom demonstrations.  I'm

>  getting tired of burning dry ice to no effect.

>

>

I made one many years ago when I was about 15.  Used a peanut butter jar

with

a felt wick around the inside of the top.  Placed isopropyl alcohol on the

wick and closed the jar with an ore source inside.  When inverted over dry

ice, the cold bottom layer was supposed to show tracks. Results were

inconclusive.  Later I used a better unit with a black water background, a

rubber bulb for pressure and a strong light source across the black field.

That one worked fine and compressing the bulb to essentially heat the vapor

saturated air in the chamber, then releasing the bulb to make it

supersaturated caused it to work well and give a short duration where tracks

were easy to see.  The water moved up and down, not causing the air to move,

thus keeping the tracks in place.



So, here is what I suggest.  Use a collimated bright beam across the field.

Make sure the background is black. You need a way to clear the field after

several tracks are formed or it just gets cloudy.  Use a strong DC electric

field or a strong magnetic field to do that, then turn it  off and watch.

You

can see alpha particles and their path length in air.  Fascinating!



Boy that was a long time ago...



John Andrews

Knoxville, Tennessee



Note: Put a series resistor in the DC field circuit to prevent any current

flow.  Current should be limited to less than a few mA if it shorts out or

is

touched by anybody.







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