Physics Demo Number: 106

Approximate Run Time:30 to 50 min

Demonstration Cloud Chamber

Demo Description

A large chamber is prepared with super

saturated alcohol vapor with the help of liquid nitrogen

cooling to capture ionization tracks of particles

passing through its critical volume.

Scientific Principles

Particle Tracks in Cloud Chambers
Cosmic Ray Tracks left in passage through supersaturated volume

Equipment & Set Up

Cloud Chamber on Dedicated Cart
Liquid Nitrogen Dewar

Equipment Location

Chamber and Dedicated Cart stay along back left wall in SC4228 .
Dewar lives in [D-4-1]

Instructions

PLEASE note that this demonstration is quite intensive in time used, especially for large classes.

Among other things, one must fill the LN2 pans completely in real time in class and be prepared to set the chamber off of the base and refill the pans again.

The dedicated cart and the chamber are seen in the first photo. Some of the numerous supporting components are on top of the chamber and the cart.

Other components are stored in the shelves of cart.

The supporting foundation for the chamber itself is seen in the second photo. The four aluminum pans have to be filled with liquid Nitrogen. On the left side of cart-top rest

1) the light source for viewing of tracks

2) the high voltage supply (for a vertical electric field in the sensitive volume during chamber operation)

3) the bottle of anti-fog compound for treating the top surface of the chamber body's glass top before cooling starts.

One must place the chamber body itself, seen in the third photo, on top of its cold foundation after having poured a (80 to 90)% 200- Proof Ethanol / (20 to 10)% Water solution on the felt which runs all the way around the top edges of the chamber body.

(Once the felt edges are thoroughly saturated with the ethanol, one pours the remaining part of the pint(+) solution into the bottom of the chamber body.)

The glass chamber-body-top is seen in the fourth photo with the chamber skirt resting on the top's upper surface.

The skirt is placed around the bottom of the chamber body to seal out air currents between the chamber body and the foundation.

Cutting down on air currents allows the liquid nitrogen to do its cooling job longer.

The fifth photo shows the skirt in place and the correct end of the chamber-body towards the dedicated light source.

The sixth photo shows the ethanol container and dedicated mixture bottle as well as a better view of 1.3 of the previously mentioned top felt edges of the chamber body needing saturation with the alcohol/water mixture before cooling is started.

Various radioactive sources are in the brown box in the cart shelves area.