Why Isn't My Cloud Chamber Showing Tracks?

[Thundagere]

I was working on my cloud chamber today, and I ran into two problems:
A) It's not working :) To be more specific, I used compressed air to get the bottom extremely cold. The structure itself is a small plastic throw away cup, with a sponge with 91% alcohol stuck to the top. The bottom (the open end of the cup) is covered in a thin metal plate, and I spray the air onto that. It gets really, really cold. However, I was unable to see any tracks. Is this because i don't havea radioactive source? I thought I might be able to see a muon or positron every now and then, but I guess not...
Also, once I was done, a purplish liquid was remaining in the cloud chamber. Could this be a product of the difuroethane from the duster and the isopropyl alcohol? I'm not sure about this.

The purple liquid. I got it into a tube as soon as it came, since I'm still not sure what it is.
http://imageshack.us/a/img525/7906/20121122131134.jpg

The set up of the cloud chamber. It looks nasty right now, but that's mostly because of the liquid. Metal bottom, sealed with plasticine. Sponge on top. Black background.
http://imageshack.us/a/img831/1209/20121122131226.jpg
Any help would be appreciated!

UPDATE: The liquid is definitely primarily alcohol based. I did some tests, and it's definitely flammable (don't have much left now, lol), and smells like alcohol. I'm just not sure what gives it the purple color.

 

[mfb]

Are you sure you have oversaturated alcohol (?) there?
A radioactive source would increase the number of tracks, but you should get tracks based on natural radioactivity without, too. Something like a few tracks per dm^3 and second.

 

[Thundagere]

Are you sure you have oversaturated alcohol (?) there?
A radioactive source would increase the number of tracks, but you should get tracks based on natural radioactivity without, too. Something like a few tracks per dm^3 and second.

I'm pretty sure. It's 91% which should work. I soaked the sponge throughly too.

 

[FeynmanIsCool]

may guess is that that the alcohol caused some reaction in the sponge or cup? Try using 99% propylene (you can get it cheap online)

 

[Thundagere]

Why wouldn't 91% work though? Or does it take time? I think I only waited about 10 minutes,since I have a limited supply of canned air.

 

[The_Duck]

I've used 91% isopropyl alcohol successfully in a similar cloud chamber, so that shouldn't be the problem. Since you don't mention this, my guess is that your lighting is interfering. You need to be in a very dark room (I also had some success outside at night). Then shine a flashlight into the chamber. Like you I taped a piece of black paper to the back side of the chamber, on the inside, for better contrast.

Play around with the angle of the flashlight. Even before you see any tracks, if it's working properly you should see a fine mist falling on the inside of your chamber. If you can see this mist you can probably also see any tracks that might show up. If you can't see this falling mist I don't think you'll see any tracks.

My cloud chamber had, at a guess, three times the volume of yours. Without any radioactive sources, I saw something like a track per minute on average (I assumed from cosmic rays, but maybe it was actually local background radioactivity? Which one dominates?).

Time might be an issue. It takes a little while (5 minutes?) for the air in the chamber to cool down, and the mist doesn't start falling until then. And you might only see a track every 5 minutes or something. I used dry ice instead of compressed air; it's cheap and you can get a nice big chunk of it that will last 24 hours.

If you pry the americium source out of a smoke detector and put it at the bottom of your chamber, it will shoot off tons of alpha particles, producing many tracks per second if things are working properly.

 

[FeynmanIsCool]

Why wouldn't 91% work though? Or does it take time? I think I only waited about 10 minutes,since I have a limited supply of canned air.

Try using Dry ice instead of canned air. It will work MUCH better.

 

[Thundagere]

I've used 91% isopropyl alcohol successfully in a similar cloud chamber, so that shouldn't be the problem. Since you don't mention this, my guess is that your lighting is interfering. You need to be in a very dark room (I also had some success outside at night). Then shine a flashlight into the chamber. Like you I taped a piece of black paper to the back side of the chamber, on the inside, for better contrast.

Play around with the angle of the flashlight. Even before you see any tracks, if it's working properly you should see a fine mist falling on the inside of your chamber. If you can see this mist you can probably also see any tracks that might show up. If you can't see this falling mist I don't think you'll see any tracks.

My cloud chamber had, at a guess, three times the volume of yours. Without any radioactive sources, I saw something like a track per minute on average (I assumed from cosmic rays, but maybe it was actually local background radioactivity? Which one dominates?).

Time might be an issue. It takes a little while (5 minutes?) for the air in the chamber to cool down, and the mist doesn't start falling until then. And you might only see a track every 5 minutes or something. I used dry ice instead of compressed air; it's cheap and you can get a nice big chunk of it that will last 24 hours.

If you pry the americium source out of a smoke detector and put it at the bottom of your chamber, it will shoot off tons of alpha particles, producing many tracks per second if things are working properly.

I'll definitely try the night thing. I can see the mist falling for sure, so I guess I'm doing something right. I've switched to a smaller jar for now.
One thing, should I wait a while? If the sponge has alcohol, should I wait for it to evaporate, then start the freezing?
I've considered the americanum thing, but I need to find a spare smoke detector around here somewhere.

Try using Dry ice instead of canned air. It will work MUCH better.

FYI, the purpose of this experiment was to see whether it could be done reliably with canned air, and see if there are any other factors that need to be taken into account :). I guess I should have mentioned that, but I would rather not use dry ice or peltier coolers, as that defeats the purpose of the experiment.
Thanks for the help!
Any ideas on what the purple liquid might be? I'm thinking it could be pure, 100% alcohol. At -40 odd degrees celsius, the water would have frozen, but not the alcohol. leaving that purplish residue. It's definitely alcohol based as it burns fine, and smells of alcohol.

 

[The_Duck]

FYI, the purpose of this experiment was to see whether it could be done reliably with canned air, and see if there are any other factors that need to be taken into account :). I guess I should have mentioned that, but I would rather not use dry ice or peltier coolers, as that defeats the purpose of the experiment.

You might get the setup working with dry ice and then switch to compressed air and see if it still works. Good experiments have control trials!