Help With A Cloud Chamber?

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acaldarone
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Help With A Cloud Chamber?

Post by acaldarone » Mon May 14, 2012 2:39 am

Long term I plan on making a peltier/TEC-based cloud chamber, but while I keep searching for peltiers capable of the wattage necessary, I decided to build an interim dry-ice based chamber. I went to American Science and Surplus and picked up a Nalgene desiccator to be the foundation of the chamber. Here's a link to the model I used: http://www.usedlabequipment.com/images/ ... ccator.JPG

. I painted the metal plate black to allow for a backdrop for the trails to appear over. I insulated the lower half by lining it with sponges and aluminum foil so it could withstand the temperatures of the dry ice. The holes in the plate also provided an easy way to mount radioactive samples (my Americium 241 piece fit perfectly both placed facing up and when tilted horizontally). I placed an isopropyl 91%-soaked sponge in the top of the upper section. When that didn't work, I tried lining the lowest 1.5 inches of the upper half with soaked felt.

In both cases I was unable to achieve the necessary state of supersaturation. The alcohol vapor simply condensed on the plate. What could be the problem? I tried warming the top with my hands, and then placed it under a heat lamp after that didn't work, to increase the temperature gradient, but still no luck. What could be the problem? Could it also be that sublimating CO2 is flooding the chamber and chocking off condensation?

hjerald1
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Re: Help With A Cloud Chamber?

Post by hjerald1 » Mon May 14, 2012 4:42 am

Some pictures of your setup might make it a little easier to help you..

However, most folks use ~99% isopropanol, which seems to supersaturate the chamber more effectively than does the alcohol with more water content.

Also the following link might give you some ideas of where to find pieces to build a
Peltier-based chamber:
http://www.instructables.com/id/Make-a- ... r-Coolers/#

Also use the search function on the Forum to see what others here have done with cloud chambers.

Good Luck,

Jerry

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Carl Willis
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Re: Help With A Cloud Chamber?

Post by Carl Willis » Mon May 14, 2012 4:36 pm

Having built a few cloud chambers, I can offer some general advice.

-The alcohol used should be as free of water as possible. I recommend anhydrous methanol ("Heet" in the yellow bottle from an auto parts store, costs about $1.50). I have seen drug-store iPA and Everclear work in cloud chambers; however, these wet alcohols are more particular to chamber conditions.

-You need to establish a thermal gradient in the chamber. This takes some time, a few minutes at least, and in the long term it also requires a sufficient heat source at the TOP of the chamber (chambers sometimes work for ~20 minutes and then stop due to lack of a sufficient heat source).

-Be careful that your radiation source doesn't swamp the chamber. 1 microcurie of Am-241 is an extremely strong source for cloud chambers and this may be why you are getting no visible action. You can increase the tolerance of the chamber for high-rate sources by applying a vertical electric field of >1kV/m to sweep ions out of the active volume.

-Lighting is vital to visualizing particle tracks. Make sure you have a strong light source illuminating the active region.

A few other general pointers:

-Avoid acrylic as a construction material. Alcohols will destroy it rapidly. Polycarbonate works better. Your Nalgene container may be polycarbonate, I don't know.

-You must have a WELL SEALED chamber to eliminate air currents that prevent the right conditions from forming. Sealing can be accomplished with vacuum grease against the baseplate, and the other parts of the chamber must be sealed as well.

-Strong performance in the long term can be guaranteed by putting a watt or so of heat into the alcohol reservoir at the top of the chamber. A resistor or some nichrome run under the sponge / felt / etc. works well.

Photos would help diagnose your issues.

-Carl
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Richard Hull
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Re: Help With A Cloud Chamber?

Post by Richard Hull » Mon May 14, 2012 8:38 pm

CO2 should never be part of the chamber. It has to be isolated from the system. The dry ice is usually in a thermally conductive pan under the chamber's sealed metal floor to keep it cold. As Carl notes, no air currents should be admitted to the sealed cloud chamber. It needs to be sealed as well. Patience is needed in chamber operation. Small chambers stabilize more quickly, as a rule.

Good luck with this project. Cloud chambers are cool.

Ricahrd Hull
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acaldarone
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Re: Help With A Cloud Chamber?

Post by acaldarone » Thu May 17, 2012 3:28 am

All I'm waiting on ATM are the peltiers, some thermal paste, and I'm still mulling over what to make the chamber out of.. American Science and Surplus had some, but they didn't have adequate wattage for the job. I just gutted some old computers ahead of a community electronics-recycling collection this Saturday. I got an ATX power supply and a Thermaltake V1. I also pulled out a soft blue light (not sure what to call it, it's not LED, it was a decoration in a see-through case), and I'm wondering if it would make a good light source for the chamber. I'll get some pics later if I can. As for the 91%, I tried salting the water out (also from an Instructables IIRC), but it didn't work. Could it be that I was using sea salt? It was still non-iodized per instructions. I'll look into Heet. Hell, might even be some in the garage right now.

Here's a pic of the cloud chamber v1. Yes, it's polycarbonate, so alcohol isn't a problem. The blue half is the bottom, with the dry ice resting in the chamber, the swiss-cheese metal-plate is covered in aluminum foil and painted with permanent marker (when I initially had it covered), which rests on the gray weather-striping tape (which from what I could see, had form-sealed, but it may have opened in the extremely cold conditions). The alcohol soaked sponge is in the top. The black loops of electrical tape sealed the top off from the bottom, but that too might have lost it's seal in the cold conditions.

Without an active heating system for the top, what would be a good way to create the gradient. Pre-heating? Could I leave it out in the sun for about 20 minutes? Was my hand warming not penetrating the polycarbonate? As for active heating, it wouldn't be that hard to work something through the top.

Is an electric line really necessary? What exactly did you guys have in mind? I heard you could just place a statically-charged Styrofoam cup on top in some cases to clear away stray ions. If not...what exactly would I need to make a 1kV/m electric field? Alternatively, could I just make a magnetic field with a simple circuit, like a battery and wire?
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Carl Willis
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Re: Help With A Cloud Chamber?

Post by Carl Willis » Mon May 21, 2012 5:04 pm

Hi Andrew,

It appears that you're putting dry ice INSIDE the chamber (correct me if I'm seeing this wrong). If so, that's a no-no as the dry ice will continuously be spraying off plumes of gas that disrupt the settled atmosphere you need. Dry ice must be outside the chamber.

The electric field and the heater are not strictly required for operation. I think you should avoid those bells and whistles until the fundamental problems are addressed and you can get basic cloud chamber behavior. Take the Am-241 source out of the chamber since in my experience it is likely to saturate the chamber. You'll have plenty of natural radiations in the chamber volume to know when it's working.

Salting the water out of drugstore alcohol sounds like a real drag. Just buy the $1.50 Heet. It'll last for months of heavy use.

-Carl
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acaldarone
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Re: Help With A Cloud Chamber?

Post by acaldarone » Tue May 22, 2012 1:01 am

Yes, dry ice is in the chamber, but the two sections are sealed off from each other by the black metal base (at least, in theory). There might be some microscopic out gassing occurring that might be seeping through the weatherstripping and disrupting things.

I'm tempted to drill a hole in the base of the dry ice containing section. Hopefully to provide an alternative exit for the gasses, instead of popping out the top.

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Re: Help With A Cloud Chamber?

Post by acaldarone » Sun May 27, 2012 7:31 am

SUCCESS. Well, sorta...

Not for my original chamber, but I got a small test-chamber working tonight. It was made from a cat food tin, felt, and the inside base was covered with a cut piece of garbage bag. It was sealed using plastic wrap with a rubber band. I tried both the 91% isopropyl as well as the methyl from Heet (more on this later). I would pre-warm it for several minutes, initially by placing a hand-warmer on the top, and then with a desk lamp. It actually caused the plastic wrap to bulge out slightly. It made a good indicator of when the chamber was ready to be placed on ice, and when it needed to be taken off ice (inversely, when it became concave).

It was actually a last-minute thing. We were out getting shakes, and the place also sold dry ice, and one thing led to another...

Anyway, it was more or less just to test whether the Americium 241 emitter would be a viable source for the full cloud chamber or if it would swamp the chamber as Mr. Willis suggested. I'm happy to say the emitter worked fine as-is. I experimented with using statically charged strips of tape and packing peanuts, as well as a small electromagnet, but none was necessary. The Americium made clean, visible tracks.

Oddly, Heet didn't work well. It made supersaturation, but it did not show tracks well. I switched back to the 91% iso and that worked much better. If Heet watered down?

acaldarone
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Re: Help With A Cloud Chamber?

Post by acaldarone » Sun May 27, 2012 7:37 am

SUCCESS. Well, sorta...

Not for my original chamber, but I got a small test-chamber working tonight. It was made from a cat food tin, felt, and the inside base was covered with a cut piece of garbage bag. It was sealed using plastic wrap with a rubber band. I tried both the 91% isopropyl as well as the methyl from Heet (more on this later). I would pre-warm it for several minutes, initially by placing a hand-warmer on the top, and then with a desk lamp. It actually caused the plastic wrap to bulge out slightly. It made a good indicator of when the chamber was ready to be placed on ice, and when it needed to be taken off ice (inversely, when it became concave).

It was actually a last-minute thing. We were out getting shakes, and the place also sold dry ice, and one thing led to another...

Anyway, it was more or less just to test whether the Americium 241 emitter would be a viable source for the full cloud chamber or if it would swamp the chamber as Mr. Willis suggested. I'm happy to say the emitter worked fine as-is. I experimented with using statically charged strips of tape and packing peanuts, as well as a small electromagnet, but none was necessary. The Americium made clean, visible tracks.

Oddly, Heet didn't work well. It made supersaturation, but it did not show tracks well. I switched back to the 91% iso and that worked much better. If Heet watered down?

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Re: Help With A Cloud Chamber?

Post by jcs78227 » Sun Jun 03, 2012 10:17 am

Andrew Caldarone wrote:
> Yes, dry ice is in the chamber, but the two sections are sealed off from each other by the black metal base (at least, in theory). There might be some microscopic out gassing occurring that might be seeping through the weatherstripping and disrupting things.
>
> I'm tempted to drill a hole in the base of the dry ice containing section. Hopefully to provide an alternative exit for the gasses, instead of popping out the top.

Andrew,

That black plate looks like the standard desiccator plate that comes with this type of vacuum desiccator. From examining the wrap around it, I can make out the shape of a large central hole typical of the plate. Beneath this plate is where one would normally place the desiccant if you were using it for drying purposes. If you have tried to make that a separate chamber to hold the dry ice, I think that's the first place to look. Trying to make that lower area gas tight is a challenge, and as you noted, the dry ice is sublimating and thus creating a positive pressure in what is at best a tenuously gas tight region. I think if you haven't given up on this, it's probably time--the dry ice belongs outside the chamber entirely.

The Heet you're using, it's the original--Yellow bottle? It's mostly nearly 100% methanol, with xylenes and a few proprietary ingredients as corrosion inhibitors. I'm surprised that you got results with 91% isopropanol. When we set it up, and this is just how we do it, we use 100% Ethanol, absolute & dehydrated (that's non-denatured & anhydrous), ACS reagent grade. Even Everclear, which works for some, is still wet. This seems to work very well with a minimum of hassle. You have to pay the excise tax as it has not been denatured, but otherwise it's great.

Good luck on your project. Hope to see more as you progress to a Peltier cooled cloud chamber.

Regards,
-Jonathan

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