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.

So it appears that I have run into a little problem...My computer power supply went bust! Mind you, it was only $17 from Addison Electronics, so don't buy power supplies from there if you know the franchise (my friend had a similar experience with one which just did not supply any voltage). So they're defective. I opened it up and thought that maybe the capacitors were busted, but they were fine; the voltage is just getting lost somewhere...Anyhow, I'll probably buy another one soon to get this project under way. I have a 13V supply that I could use, but I need more power than the box provides, since the peltier coolers suck up quite a bit of energy. In other projects like this they sometimes use a couple of power supplies like laptop chargers, but that's a bit of a hassle so instead I would prefer to use one power supply for the LEDs, peltier coolers and cooling fans instead of splicing and soldering wires everywhere. I'll keep updating on the power supply situation.

Fun with peltier coolers!

So here is a couple of photos of the materials I gathered to make this electrically powered cloud chamber: I have a regular computer power supply (that broke on many occasions), a massive microprocessor heat-sink, thermal paste, solder, soldering iron, archaic voltmeter and of course the source of my frigid environment--the peltier coolers! the coolers are made of copper and bismuth, when an electric current runs between the two metals, heat exchange takes place resulting in one side that cools and the other that heats up (hence the use of the heat-sink to remove the excess heat). But it's missing one critical component...the source of radioactivity! I use Americium 241 since it's commercially available in smoke detectors (it's a tiny piece of metal enclosed in a metal casing). These coolers are needed to supercool the alcohol vapor, so an efficient thermal transfer is necessary to prevent overheating one side of the peltier coolers. To do this I will use regular thermal paste to increase the medium of contact through which the heat transfer can take place.

Next time, the building begins!

Theory behind the project.

Before the era of computers and detectors, the only way to detect the paths of elementary particles was to use cloud chambers. A cloud chamber is a closed system containing air that is saturated with alcohol. Applied to this system is a heat gradient usually done by cooling the bottom with dry ice and leaving the top at room temperature. Usually alcohols are solids at -80 (temperature of dry ice), but due to this gradient they do not solidify in the air and are cooled way below their freezing point and thus termed "supercooled". This supercooled alcohol becomes very sensitive to minute disturbances and can condensate in mid-air. Scientists discovered that this was a very useful method for visualizing the trajectories of charged particles: electrons, muons and alpha-particles. While primitive nowadays, cloud chambers were an integral step in the early particle physics experiments.

Particle trajectories and interactions visualized via cloud chamber.