Cloud Chamber

From Mainsequence

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Source material for this page is being transferred from this original version.

• Start and Map pages
• MainSequence 1: Cloud chambers and cosmic rays
• MainSequence 2: The stardust hypothesis
• MainSequence 3: Little toy universes
• MainSequence 4: The photoelectric effect
• MainSequence 5: Casting dice
• MainSequence 6: A physical calculation
• MainSequence 7: Photon deflection
• MainSequence 8: Electromagnetic prisms
• MainSequence 9: Some polar science
• MainSequence 10: Watershed hydrology
• Main Sequence 11: Lunar shenanigans
• Main Sequence 12: An infinite quantity of mathematics
• Main Sequence 13: Remote sensing of the environment
• Main Sequence 14: The Rock, some math for a younger person

Contents 1 Introduction 2 References 3 Backstory 4 Back-reference

Introduction

Cloud chambers (originally invented to study clouds!) are simple passive transparent boxes with a very interesting characteristic: They can record the passage of subatomic particles in their interior as vapor tracks. Below is an example and this page is about how to build them and what might be seen inside.

References

• The Cavendish Laboratory outreach website

Backstory

It dawned on me while reading a little physics history that progress in early 20th century experimental physics relied in part on cosmic rays as a source of phenomena. Since the premise here is 'don't take anybody's word for it' I'll begin by putting two statements on this page:

• I should do this premise justice with digressions into early 20th century experimental physics, the word phenomenon and the term cosmic ray.
• I shall now completely ignore What Anybody Else Says, take the hint, build the device, and then stare at it for awhile to see for myself if myriad invisible particles are zooming through space everywhere...

To begin with, I'm going to go buy a fish tank, a little glass fish tank.

The width of this apparatus can be small, perhaps 30 centimeters across or less. Dry ice tablets are sold at the Service Desk of many supermarkets, where you may wish to accompany them into a back room to pick out a good block of the stuff. It tends to run 1USD per pound.

The chamber is a transparent box--I've used both glass and clear plastic--and is open on the bottom to accommodate the metal plate which in turn couples well to the dry ice. When placing the apparatus on the dry ice it can be weighted down and will pressure-ablate itself into the dry ice in a few minutes. The entire apparatus will tend to reach its operating temperature in a matter of half an hour or so.

The felt or cloth is traditionally black and is adhered to the interior of the glass box, both a band around the perimeter near the top and a rectangular patch adhering to the metal plate at the bottom. One could also place a rectangular patch on the "ceiling". This felt is soaked with "pure" (like 99%) isopropyl alcohol or another alcohol spirit that will continuously evaporate off the felt. The top of the chamber will start out at room temperature and the metal plate in good contact with the dry ice will become very cold. The net effect is that the interior of the chamber will be filled with a cold alcohol mist or drizzle and will be very prone to condensation.

During operation the chamber should be pretty well airtight, the more closed the better. Particle tracks are said to appear as vapor trails under good operating conditions. These two remarks suggest two modifications to the design not shown in the schematic: First, if the particles are charged and a reasonably strong magnetic field is present, the chamber tracks might show some type of deflection. A magnetic field could be introduced for example by stacking "NIB" magnets on the steel plate or by introducing some sort of electromagnet either internally or externally. The idea could also be extended to introducing electrical fields, for example between a pair of charged plates, although care would be necessary since the interior of the chamber is filled with damp flammable vapor.

Second, a simple pump could be coupled to the interior of the chamber in order to suddenly reduce the interior pressure. This approach was taken by Wilson in his original design of the cloud chamber in order to induce vapor condensation. Anecdotally this mechanism might produce a sudden 'batch' of condensation tracks. Being able to create tracks on demand could make them easier to see and could also facilitate photography.

LEFT OFF HERE

(The next step in the main sequence is the Stardust Hypothesis.)

Back-reference

(The original source material is in transfer to this wiki... it is a set of very cumbersome web pages but is also more complete at the moment (1/2008).)