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Do you think manual bottle pumps make a good enough vacuum for a cloud chamber if the contents are water and dry ice, and the bottle is colorless?   

Wite Mr · Posted 16 Nov. 2020

Kevin Zhang
@Kevin · Posted 16 Nov. 2020

Diffusion cloud chambers, the type that use dry ice, do not require vacuums. They operate at atmospheric pressure and rely on the formation of a supersaturated layer of atmosphere (saturated with an alcohol, typically) to create the environment where ionizing particles produce cloud trails.

Diffusion cloud chambers are the easiest to make, and the most suitable for demonstrations or home experimentation, being simple, easily assembled from common material, and are in addition continuously sensitive. Their primary drawback is the thin zone of sensitivity.

Wilson cloud chambers use a sudden drop in pressure to create a radiation sensitive environment in the entire cloud chamber. But a hand pump won’t do. It does not need a good vacuum, the pressure drop is modest, but it must be fast and not produce turbulence. This is done either with a diaphragm that flexes up and down or, in a much more complex design, a piston. The expansion ratio is something like 1.05 to 1.40. These chambers are only sensitive briefly. They often operate cyclically, several times a second, with a synchronized camera to capture images on each cycle.

Making a diffusion cloud chamber only requires a glass or jar, a block of dry ice, a metal sheet bottom (perhaps the jar lid), an absorbent material wetted with isopropyl alcohol, a black surface for visibility from above, and a good light source to illuminate the active zone (bright uniform light is best). Slide projectors (rare now) were good illumination sources, but flashlights with a bright white single LED and a lens are excellent (“LED tactical flashlights”, by Cree and others are of this type)

Kevin Zhang
@Kevin · Updated 16 Nov. 2020

This is very good, worth having.

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