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kafka
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[*] posted on 26-7-2006 at 18:42
Particle detectors


hi everyone, im new here so sorry if this is in the wrong forum .
anyway, i recentley went to the exploratorium and witnessed for the first time a cloud chamber in action. it was absolutley fantastic! and now im dying to make one.

actually (dreaming here) i really want to make a table with a glass top with a cloud chamber underneath. that would be absolutley fantastic!

but im running into problems in the design....

first off diffusion chambers seem to be the way to go. but i do not want to go buy dry ice every 8 hours to look at my coffe table! how about propane instead? simply running the propane through an improvized ac unit could keep the bottom of the chamber cold right? im thinking a copper for the bottom of the chamber with probane being squirted in one side and pulled out the other to go into the compressor and out through coils with a fan then back into the copper chamber.

ok if that idea is no good, how about using somethign besides water or alcohol in the chamber? can an ethylene glycol fogger be used to fill the cloud chamber? im guessing no because otherwise it would be more commonly used right?

is there a reliable way to use the decompression design but with a vacuum pump or something?

i have several other idea but before i embaress my self anymore id like to hear something from someone who knows what they are talking about...

thanks

chris

ps: if anyoen has a better idea for a visual particle detector that i could place into the top of a glass coffee table let me know!
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[*] posted on 27-7-2006 at 05:35


Hey Kafka...I'm not sure how deep your understanding of a cloud chamber is - I agree they are amazing to watch. Especially if you place a fairly active piece of a radionuclide inside it that is heavy in beta and or alpha emissions.

As far as cooling your scaled-up "coffee table sized unit" you're looking at several things. First off you need to pick a vapor material that can exist at room temp and 1 atm (for simplicity) as a supersaturated, supercooled gas. Namely alcohol in most cases. The key in your design would revolve around finding the right material that could be easily cooled to the supersaturated condition using an improvised AC unit. FYI, dry ice is around -110F. Waaaaaay below what a typcial AC unit is capable of. So that is out.

If you can find a solvent that exhibits the supercooled properties at a higher temp (and use a freezer compressor/condenser/evaporator) you might be on to something.

Now, the problem with this "new" solvent is the fact that it is most likely going to be toxic. The amount contained in a coffee table is going to be non-trivial and now you've got a hazard in your house rather than a cool vapor trail show! :( Not something I want sitting in my house! :cool:

The other reality check on this thing would be the fact that you would have to be so close to the glass to see the trails. Since you just about have to put your nose up to the window to see the effect, you might as well just stick to the jar type rig. I doubt if a coffee table sized unit is going to show visible tracks at normal sitting distances...

Maybe some others here can offer further advice... Good luck!




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PacketStorm
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[*] posted on 27-7-2006 at 05:43


Oh, I almost forgot. As far as those propylene glycol foggers go - nope, that won't work. The very fact that the PG comes out as a fog right off the bat precludes its use in a cloud chamber. You need a vapor that stays in gaseous form until a nuclear particle comes smashing in and strips the electrons off the air/gas inside, ionizes it and makes the vapor condense.

If you are willing to spend some cash, unitednuclear.com has a very cool, self-contained table-top unit that is under $300. It even has a high intensity lamp and a high voltage grid at the top of the chamber to help push the condensed vapor down to the bottom of the chamber.

Of course, in the name of mad science you would want to build your own, right? :D




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Tacho
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[*] posted on 27-7-2006 at 09:17


I have never built one, but I suggest you build a small one first. Test different solvents, pressures and temperatures and then try to scale it up.

Have you read the Scientific American's "amateur scientist" article on homebuilt cloud chambers?




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[*] posted on 27-7-2006 at 11:35


Quote:
Originally posted by kafka
anyway, i recentley went to the exploratorium and witnessed for the first time a cloud chamber in action. it was absolutley fantastic! and now im dying to make one.


I work there. :)

I've always wanted to nab the master key, open it up, and sprinkle a couple grains of uranyl nitrate inside heh.

Quote:
Originally posted by PacketStorm
If you are willing to spend some cash, unitednuclear.com has a very cool, self-contained table-top unit that is under $300.


I have heard good things about the $225 United Nuclear one, although they seem to be 'temporarily sold out' right now. If I were you, I would try one of those babies out, see how it works for you, get a good, hands-on understanding of its workings, and then maybe butcher it for parts for your coffee table (or find similar parts elsewhere).
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kafka
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[*] posted on 27-7-2006 at 22:17


THanks for the advice everyone!
so it looks as if my choices are to either experiment with different solvents, to make an expansion chamber, or to mess with the temp.

how about a not so volatile liquid and a heating element on the top? then a 0 degree bottom plate?

what about expansion chambers? i cant seem to find out how long the effect last with these things. after the pressure change do you only have a second or two? how about a random series of inexpensive expansion chambers that go off at differnet intervals?

any ideas on solvents? im ok with toxic stuff, ive handled plenty in my time.

thanks everyone, the girlfriend and i really hope to get this one going this weekend, id love to take photos of the process and post them.
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[*] posted on 28-7-2006 at 06:27


Acetone aparently works fairly well.

You may find it useful to look at Peltier modules, which aparently produce enough of a temperature difference to run a cloud chamber. Modules and regulators are available from as little as a few tens of dollars. All electric, no moving parts. You will need a big heatsink on the hot side.

The United nuclear cloud chamber has always looked rather expensive to me.
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[*] posted on 28-7-2006 at 07:44


Good idea Marvin. Those peltiers can really get down there in temp - especially if you liquid cool the hot side. It would certainly be a lot quieter than a conventional compressor based system. :D Perfect for indoor use...



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kafka
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[*] posted on 28-7-2006 at 23:54


Peltiers! yes i have never heard of them untill now, but after some research they sound absolutley awesome! the only problem im having is finding large ones, like in the 2 by 2 foot size. is this neccessary? could a simple 50mm by 50mm peltier cool down a 2 by 2 foot copper plate enough for the desired effect? the heat sink on the bottom would definetley be submerged in some recirculating water. im not sure if just one will do the job, but sandwiching them together sure could get the temp down low enough!

ive done some research but im not finiding a few things. if these things get very expensive in such large sizes would it be practicall to make my own sandwiched peliter with differnet metal plates? or would that bot be energey sufficient? i found one web site that sells small cloud chambers using these things so this is possible!

http://nebelkammer.phywe.de/en/cloud.html

thanks again everyone! i hope to start building or at least buying materials tomorow!
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[*] posted on 29-7-2006 at 01:33


Peltiers don't use metals, they use semiconductors; bismuth telluride being the standard one. Beyound that, trying fab something very large to the tolerences needed is beyond most hobbists.

Overview at these links:

http://www.ferrotec.com/technology/thermoelectric/

http://www.ferrotec.com/technology/thermoelectric/thermalRef...


As for how much can they cool down - units are rated with a curve that gives temperature drop vs amount of heat pumped vs hot-or-cold plate temperature. So to answer your question, you will first need to figure out the heat flow into the chamber, so you will know how much heat you'll need to pull out. Note that thermoelectric cooler are not very efficient, they generate much more heat than they suck in on the cold plate; this means that they are not the best choice for big cooling jobs.

These guys make larger units, and have free software to help determine your needs, you can download

http://www.thermoelectric.com/


And this is a 2 ft x 2 ft chamber under construction

http://www.lns.cornell.edu/~menon/Cloud.html

some of their internal links are broken, a well worded email might help you get to the missing parts.

One problem with really large units is the difficulty in maintaining a sufficently uniform environment across the width of the chamber. Fresh vapour must be introduced from the sides of the chamber and flow across the width. To avoid getting a cool spot, possibly with downdrafts, in the center you will need to use a double or even triple paned window.

As an alternative to full table-top size, you could make a smaller chamber and project it onto a translucent screen that forms the table top. This would also enlarge the tracks, so you could see them at a reasonable distance

Or you could write a cloud chamber simulation, and use a large flat screen moditor for the table top.
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Marvin
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[*] posted on 29-7-2006 at 08:53


A small unit with a peltier is feasable without too much difficulty. For a 2ft x 2ft unit you would have to go for something else. Simply stacking lots of peltiers together will work badly and require a huge amount of power. It may even thermal avalanche if the control units arn't properly protecting the modules. The biggest issue is getting the heat away from the hot side, so its a very big heatsink or a liquid cooling method.

From what I can tell a big issue is the depth of the supersaturated layer in the running chamber, some designs have rather narrow active volumes and no information on how this can be avoided.
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smile.gif posted on 1-8-2006 at 21:30
improved plans


Well ive taken a little of everybodys advice and i have changed my plans. My girlfriend and i made our first cloud chamber the other day with a mason jar, a pie pan, a sponge, and some denatured alcohol. we got results! they were hard to see because my light source was weak (flash light), the dry ice quickly sublimes, the jars shape made viewing hard and the whole thing was not always air tight because of the quick set up. this of course was my first cloud chamber, i want to make it clear that i am skilled enough to make somethign much more complex.

so now i have new plans, i will first build a very small, very simple, but very attractive table top dry ice chamber. then after successfuly doing that, i am going to make the peltier model using a 12cm by 12cm glass "column."

i will be focusing on the the dry ice model for right now, i have two pictures of parts of the chamber stuck together. the top is a glass light cover, the middle is some steel tin, and the bottom is the hardrive from some old computer. these parts were found at a garage sale today for under $1, they have nto been cleaned but when polished they hsould look fantastic! the whole thing is 15cm tall.

i plan on filling the tin up with dry ice (or possibley a chemcial rxn that drops that low, any ideas? i have yet to investigate this idea). then a copper "rod" (not in picture) will fit snugly in the tin (with silicone lubricant) in contact with the cold mixture inthe tin. The copper "rod" will then be painted with a few thin coats of flat black spray paint. the finished copper peice will then be glued airtight into the clean globe, wich will have a strip of velvet glued to the inside top soaked in alcohol. Hopefully i will find a round and powerful light (battery operated) that will illuminate the glass sphere from the top.

So here are my questions, that im hoping you wonderfuly smart people can help me with.

1) are there any affordable replacments for dry ice? i need something cold that i dont have to buy every use. possibley some kind of chemical rxn. ( i know i should investigate this myself a little more).

2) heat applied to the top of the chamber, most likley by the light, will it help with the success of this project? the alcohol is suppose to supersaturate the globe, so a warm top and a cold bottom should work better than a cold bottom and room temp top right?

3)Any recomendations on the light to use? ecspecially if heat is going to help the performance of the chamber.

4)Any recomendations for the design? i want a simple but eligant chamber i can keep on my coffe table when not in use. im liking the way this is turning out, but im open to ideas.

thank you everyone youve been a great help.
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kafka
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[*] posted on 2-8-2006 at 19:27




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[*] posted on 11-8-2006 at 11:27


Kafka, any luck w/ the peltier cooling for your cloud chamber? I am in the design stage of making a similar unit. I would prefer not to water cool the heat sink (possible leakage, messy tubes, pumps, etc).
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[*] posted on 11-8-2006 at 16:18


Get a big heatsink with a fan then. Still feasable.

Thermal compound both sides of the peltier, do not get any in the middle and do not under any circumstances try to stack them for a bigger temperature drop.

Good luck!
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[*] posted on 12-8-2006 at 11:02


Thanks Marvin.:) I did not think air cooling of the heat sink would achieve the low temp needed. I have not seen an air cooled peltier cloud chamber, most seem water cooled.
Was considering a endothermic mix of some sort, even just ice and salt, or ammonium thiocyanate / barium hydroxide, immersing the heat sink blades into a bath of it. Messy also.
Easier to get good fans and big heatsinks, so thanks, I will try this direction.
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[*] posted on 15-8-2006 at 19:21


im actually jsut finishing up my dry ice version, a lack of funds and time is making this project move slowly. i hope to be done with the dry ice version this week ill post results. metaminct, could you give some details on how you plan on mkaing it, what solvent ur using etc? thanks, i look forward to seeing ur chamber
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[*] posted on 15-8-2006 at 22:26


I am also building a cloud chamber, it will be similar to the one on this link http://www.lns.cornell.edu/~adf4/cloud.html
But, it says you need "A clear, see-through container with an open top, about 6" by 12," and about 6" high. Make sure it is box like with flat sides, rather than being round."

well, ... it seems like it being round really does not matter does it? So why does it say top have flat sides?

Also, I would like to know if it is very important to have thin glass? To me it would seem like it would reduce the particles quite a bit, but then again I guess if they can make it all the way from outer space such as the low-energy cosmic ray, it could easily make it threw the glass right?

also i would like to know if anybody has heard what works better? acetone, IPA and so on

I guess one could guess that the lower density molecules would work best I a cloud chamber? I say this because to me it seems like the droplets would have a longer chance to get bigger, sense there less dense they wouldn't fall so fast, but also it might be the lighter molecules for they can move faster? huh actually I do not have a clue does it even matter?




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metaminct
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[*] posted on 16-8-2006 at 11:24


Kafka, I have made a dry ice unit, which works well. I intend to use the peltiers w/heatsink thermal glued directly to the Aluminum bottom of this chamber.

It's a martha Stewart brand plastic container and has a airtight
lid, not shown here. (see pic) I glued the aluminum (thin food delivery type) to the plastic with silicone caulk. Also, i cut out the bottom of the decanter, rather than cutting the side, so I knew there would be a straight edge on the bottom.

Also, I glued strips of sponge inside the upper area of the container with silicone. This unit works fine w/ 91% isopropyl alcohol in the chamber. I used dry ice pellets in a round plastic bowl so as to make good contact with the aluminum. The inside bottom of the chamber has black cloth to help see the trails.
Then wrapped towels around the whole bottom area to insulate. (Black helps keep down reflections.)
The lighting is important. I used a small Maglight,
and then a larger one with a rectangle mask over it to
produce a slice of light into the bottom area of the
chamber. Didn't have much success with larger
lamps,etc.

kclo4 , the reason for a container w/flat sides is for visibility. It's hard to see the trails through some round containers as the thickness varies (like a glass pickle jar), causing distortions in viewing. Any container with smooth and uniform sides should work.
I don't think thickness matters much for viewing cosmic radiation since some would also be blocked by walls and the roof of your house, etc. Many Betas and xray, gamma will pass right through. Also, there are radioactive sources in the environment, incl. the air inside the chamber, so I'm not sure that it's possible to tell the true origin of an individual particle trail, it's probably a mix of cosmic and environmental.
Not sure about acetone or other solvents, haven't tried yet. One problem with 91% iso is that the water crystallizes as ice on the bottom of the chamber.
The molecular density of the solvent is an interesting question. Would it affect the amount of condensation caused by the ions, or cause the trails to last longer? Would gravity have the same effect on droplets of any solvent?

Basic chamber:
http://www.imagestation.com/8122322/3984113861
http://www.imagestation.com/8122322/3984062964

Alpha particle stills:
http://www.imagestation.com/8122322/3984093762
http://www.imagestation.com/8122322/3984093752

Beta particle still:
http://www.imagestation.com/8122322/3984093747
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kclo4
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[*] posted on 17-8-2006 at 10:30


thank you, so you say you have made a cloud chamber with 91% alcohol?
thats interesting i think to me it would seem as if it would make it so it wouldnt work, like the ice crystals would make all the IPA fall out also, and make it "rain" or something

but anyways i just made me some dry IPA by adding anhydrous MgSO4 to the 91% and distilling, so sometime today i plan on making a cloud chamber yay

but with out a radioactive source, will some of the particals still be effected by a sorta strongish magnet? it seems like there would not be to many alpha and beta particals and those are the ones that are effected correct? what are the other ones that also have a charge?




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metaminct
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[*] posted on 17-8-2006 at 16:42


Interesting, it does rain in my chamber. More at first and then as the chamber cools down it lessens. Also noticed a sort of "pulsing" of the condensation layer near the bottom, after the chamber cooled down. I think a kind of equilibrium heat exchange effect??

I have not had any success observing curved trails w/ a magnet so far. Tried with and without radioactive sources, using a apx. 1" neodymium magnet. IIRC, what I've read indicates betas, of certain energies, will be affected by a magnet, and that you may need beta source like C-14 to view this.

[Edited on 18-8-2006 by metaminct]
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[*] posted on 17-8-2006 at 17:26


Probably you need a much stronger magnetic field than you can produce. I'd bet on the order of 1T over the volume of the chamber... you might get that at the surface of a supermagnet, but nowhere near any of the chamber.

Mind that your chamber is "small", so you need a strong field to observe much bending. Mind also that betas may or may not be relativistic (although I seem to recall they don't go much into the MeV range?).

Tim




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kclo4
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[*] posted on 17-8-2006 at 21:15


oh i see, well yeah i noticed that it didnt do much with the strongest magnet i have. i just built my cloud chamber today, and with my pea sized Uranium ore, i could many particals! it was great,
however!
dry ice is not my friend!


why cant ice cubes work if you heated the alcohol or somthing?
or changed solvents to somthing like DCM? chloroform?

i would really like to use frozen water instead, so i think i am gonna work towards doing so, does anybody know why this can or can not work? what i should do to make it work ect?

thank you




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[*] posted on 18-8-2006 at 06:37


Found this link a while ago:

http://www.physics.ncsu.edu/pira/7modern/7D30.html

Your post reminded me of one entry:

"A glycol cloud chamber is heated at the top and cooled with running water at the bottom"

There are source references at the end of the page.

Would be interested in hearing your results :)
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[*] posted on 18-8-2006 at 11:27


Oh thanks, I really wish finding information about the glycol cloud chamber was more abundant!

well, does anybody have an idea of how hot it should be? it to me would seem like it could be heated with a simple fish heater or something such as that, or perhaps even a candle warmer/melter thing


Anyway, even thought its pretty obvious that it is going to take a lot more work, but doesn't it sound really appealing to make a large glycol cloud chamber, that you simply need to turn on the cold water and plug something in?

OK so maybe I am thinking toluene will work, instead of doing all this research I think I might just try to make a toluene/ice water powered chamber, I think I will heat the toluene with a fish tank heater.




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