Old fashioned cloud chamber

Old cloud chamber using dry ice and Americium 241.

This is an old model I built some time ago. The acrylic box comes from an old napkin holder (hence the little studs on the top) and the Styrofoam base was cut from stereo packaging. Styrofoam is the way to go if you want your dry ice to last for a bit longer, but hopefully I don't need to find dry ice anymore if my peltier coolers work! For the bottom I used a thin sheet of Aluminium that you can buy at Home Depot or any hardware store. beneath the chamber, inside the Styrofoam there is a little pocket for putting dry ice and I placed some Aluminium foil on top of it as well as the Aluminium sheet that I sprayed black to be able to visualize the particle tracks. Along the inside of the chamber I used these sticky felt pads that are usually used to put under the legs of furniture; these ones were a bit absorbent and were able to soak up the isopropyl alcohol quite well.  I left the top and one side clear for viewing, but the glare of the plastic was always irritating and always blocked the viewer from properly seeing the particle tracks. Hopefully in my electric model the viewing angles and lighting will be better. I'm currently trying to find a thin plastic piece that is dome-shaped, but not too flimsy. I already have the rubber for the seal, but am still missing a good computer power supply; all the ones I buy end up being duds...Anyhow I thought I would post my old project just so people can have an idea of what the old version looked like.

Lighting and other issues.

One aspect that is extremely important to visualize particle trajectories is the lighting. Since the condensations are quite thin and the lighting needs to be accordingly adjusted. One thing that can be done is to make the transparent viewing chamber out of a non-reflective material, but this can be expensive and not cost-effective since there are other ways to get around this problem. Aim the light through one plane and make the viewing end on another axis (so that the viewer is not bothered by any glare or bright light). For lighting source, I use LEDs, preferably with an intensity adjuster for optimal viewing, but any light-source would be good except for maybe one that gets too hot and may create an unwanted temperature gradient across the chamber, but if it's on top of the chamber that would be okay since there should be a temperature gradient from the top to the base of the chamber (top is usually at room temperature and bottom is at about minus 80 Celsius).

P.S. I haven't tried different wavelengths of light, but they would probably work just as well as white light.

Problems finding 99% ethanol/isopropanol

Something as simple as adding salt  can separate  phases.

 

In Canada it's hard to find cool stuff...plain and simple. You can't buy liquid nitrogen or dry ice from ice cream stores like in the states, and it's more difficult to find concentrated alcohols at the local pharmacy (the max I've seen is about 70%), but for the sake of this project there is a way to get around it, and all you need is your standard rubbing alcohol, non-iodized salt and a clean glass jar. Salting out is a well known method for extracting and concentrating organic molecules like protein purification, but this can be applied to isopropanol and ethanol as well. Just pour your diluted alcohol mixture into a clean glass jar, pour salt (how much depends on the amount of water present in your diluted alcohol solution). the salt molecules have more affinity for water than organic molecules since they are very polar in terms of charge distribution. The salt sort of kicks out the alcohol into its own phase where the alcohol will float to the top and then you can take the layer with a turkey baster and there you'll have 99.9% pure alcohol! But if you can get your hands on something with 99% purity, it's probably better.

Where to find radioactive sources?

Radioactive sources can be hard to come by, but there are a few common household items that can be used as radioactive sources. The most common source to come by is Americium 241 which is the source of alpha particles used in smoke detectors. of you take it apart you'll find a little piece of metal half a centimeter wide that contains Americium 241 (in picture). Another source can be ceramic dishes which naturally contain isotopes of uranium and thorium, however the glaze can contain uranium oxides and be potent emitters as well. Even some paints containing uranium or cadmium may be emitters, but you don't necessarily need a source to see particle paths in a cloud chamber since the background (mostly muons from space) can also be seen occasionally.