Mad Physics :: Experiments
Building Wilson's Cloud Chamber

Introduction | Methods | Results | Methanol | Resources

A cloud chamber is used for detecting particles of ionizing radiation. It is an airtight, super cooled, supersaturated environment. Today we will show you how to build this device in he luxury of your own home with simple materials.

Introduction

The Scottish Physicist Charles Wilson won the Nobel Prize in 1927 for his work developing the cloud chamber (often referred to as a Wilson Cloud Chamber). In his chamber high energies of alpha and beta particles enable particles to leave trails due to the many ions that were along the path of the charged particle. These tracks have distinctive shapes. Wilson’s chamber used water vapor and looked like this (photo from www.njsas.org/projects/atoms/cloud_chamber/):

We will be using a different method though. Our chamber will be more like Alexander Langsdorf’s diffusion chamber. In this chamber dry ice cools the bottom while alcohol replaces water.

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Methods

The new set-up involves an airtight transparent container. The one we bought was from the baking section of our local grocery store. It should be completely airtight (you should test this with water before you put the alcohol in) and it should be completely see though. You should then place an absorbent material on the top to hold the alcohol. The bottom should be placed over dry ice with a metal sheet in between. The set up should look something like this:

Here is our set up:

The best way to set the experiment up is to place the alcohol in the chamber, seal it and put it in place. Then after a while there should be some mist in the container. At this point you should wait approximately 15 minutes, and then you will see the streaks created by the ions. It should be noted that the best way to see these is on a screen (i.e. you should put a light source in front of your set up so it goes through your container).

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Results

Once the mist appears and you start seeing tracks you can document these by looking at your screen. As you can see our set-up (bottom: inlay left) produces a shadow, and within that shadow there are certain tracks where the ions can be detected (bottom: inlay right). For more information take a look at our resources.

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Methanol Safety and Fun

This lab includes two dangerous elements. Dry is one of the dangerous elements, it is at -78.5ºC and it is cold enough to cause bad burns. You should know some of the dangers from our previous lab.

Methanol is also a very very nasty chemical. For this lab you need pure ethanol or methanol and we used over 99.8% percent methanol, which can make you blind or kill you simply through touch or inhalation. So make sure to use gloves and work in a ventilated area. This lab isn’t easy, so if you don’t feel comfortable doing it, don’t!

Finally, after killing the mood I thought we could have some fun. After I used the methanol I needed to dispose of it, so I decided to burn it off. So, to prove to you it was pure, look at this video (~4mb) and behold the pure blue flame produced. Also just in case... make sure to have the number for your local poison control handy. You know, just in case.

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Additional Resources

http://en.wikipedia.org/wiki/Cloud_chamber

http://www.lns.cornell.edu/~adf4/cloud.html

http://njsas.org/projects/atoms/cloud_chamber/index.php

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Cite Our Experiments & Research

If you have used any of this information or any of these images please go ahead and cite them in your bibliography. For your convenience, this is what the citation would look like in MLA format:

Family, Afrooz. “Building Wilson's Cloud Chamber.” June 27, 2005 Mad Physics. dd mmm. yyyy

<http://www.madphysics.com/exp/building_wilsons_cloud_chamber.htm">

We are glad to share our knowledge with you as long as you cite all of our info, and contact us before you use anything for non-educational purposes (commercial, etc.).

† In the bibliography you must insert the day you visited the site (this is relevant because the site could change at some point), therefore, in the bibliography above replace dd with the day you visited, mmm with the abreviated month, and yyyy with the year (ex: dd mmm. yyyy becomes 23 Dec. 2004).

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