I'm trying to make a cloud chamber to observe cosmic rays, alpha particles, etc. I don't want to use dry ice, I have tried cascaded peltier coolers on a very efficient fan cooled copper heat sink which easily reach -30 deg C. A piece of tissue wetted with 99.9% pure isopropyl alcohol is suspended with a magnet and a large washer either side of the top of the glass jar ( a large inverted coffee jar) So far I have not been able to form any mist, there does not appear to be any thermal gain between the warmer heat sink back to the cold side. The temperature is measured with a contact probe on the cooler. Total T.D is over 50 deg C between the hot/ cold side of the coolers. each cooler, 4 in total, (arranged as two in cascade, in parallel with another pair) have their own adjustable power supplies which have been set for maximum cooling at minimum current. I have tried several combinations of T.E.C's and the results are all similar. I did try water cooling the fins of the heat sink with only a marginal improvement of 3 deg colder. Still no mist, so anyone got any ideas?

 

A picture would be worth a few more words...

And, have you tried dry ice to confirm that your setup would otherwise function properly?

 

Hi, I will take a picture and upload it, not tried dry ice yet, I wanted to avoid it. On U tube there are several people who claim to have working units with peltier coolers and the ones I'm using are better spec than the ones they use. I'm wondering if its the alcohol I'm using but cant see why that would be. The stuff I've got is for laboratory use and is stated to be 99.99% pure. I am going to put the whole thing in the freezer overnight and see if pre-cooling helps.

 

I think putting the whole thing in the freezer overnight would be counter productive. You want an atmosphere saturated with isopropyl alcohol vapor which becomes supersaturated right above your cold plate. Cooling the whole box will decrease the amount of vapor phase alcohol, so if there is a supersaturated layer over the cold plate, it will be even thinner.

Rather than cooling, I would consider increasing the area of the wetted tissue. If you have a way to warm the tissue slightly, maybe a heat lamp or light bulb above it, that might help.

Be sure the box is air tight.

John

Edit: Are you letting your chamber become saturated with the alcohol vapor before turning your cold plate on? Also, my comment about warming was to get the atmosphere saturated faster. You do not just want to distill from the tissue to the cold plate. After the atmosphere is saturated, then briefly putting it in the freezer may help get a supersaturated atmosphere.

 

Do you have an alpha particle source? Are you just looking for random alpha particles?

Also, the at sop here should be supersaturated (clear, non-condensed gaseous isopropanol). You do not want clouds/aerosol. The "cloud" should only happen as the particle crashes through the isopropanol and causes nuclear ion points and the isopropanol suddenly condenses to make a contrail.

So, you may have a decent atmosphere and just need more radiation to see.

 

Thanks for the info, my source is a thoriated (2%) tig welding tip and I wonder if the alpha particles can penetrate the glass. I guess the amount of alcohol is like the three bears porridge, needs to be just right!
What I tried was to saturate the tissue, run the coolers then mop up any condensed liquid on the cooler then re-seal the jar.
I also tried keeping my hand on the top to raise the temp of the tissue a little and I'm sure that I have a jar full of gaseous alcohol.
I've seen that the ionisation device used in smoke detectors is radioactive and will try using one of these as a source.
Would wrapping lead sheet with a pinhole at one end around the thoriated rod give me a more intensified "beam" of particles?

 

Thanks for the info, my source is a thoriated (2%) tig welding tip and I wonder if the alpha particles can penetrate the glass. I guess the amount of alcohol is like the three bears porridge, needs to be just right!
What I tried was to saturate the tissue, run the coolers then mop up any condensed liquid on the cooler then re-seal the jar.
I also tried keeping my hand on the top to raise the temp of the tissue a little and I'm sure that I have a jar full of gaseous alcohol.
I've seen that the ionisation device used in smoke detectors is radioactive and will try using one of these as a source.
Would wrapping lead sheet with a pinhole at one end around the thoriated rod give me a more intensified "beam" of particles?

No, alpha particles cannot penetrate glass. They are essentially a helium atom without the electrons. A piece of wax paper or cellophane will stop them. Set the tip directly in the chamber. If there is a polymer coating or other coating on the tip that hides the thorium, that should be removed as well.

Google "mean free path of alpha particle". I think they only travel a few inches in air (if I remember correctly). Pretty low energy "radiation"

You cannot focus or direct the beam in any way with just passive shielding.

 

No, alpha particles cannot penetrate glass. They are essentially a helium atom without the electrons. A piece of wax paper or cellophane will stop them. Set the tip directly in the chamber. If there is a polymer coating or other coating on the tip that hides the thorium, that should be removed as well.

Google "mean free path of alpha particle". I think they only travel a few inches in air (if I remember correctly). Pretty low energy "radiation"

You cannot focus or direct the beam in any way with just passive shielding.

Thank you for that info, it's almost certainly why i've not seen any trails, I will put the rod inside the chamber and try again.

 

Agree completely on putting the source inside the chamber.

As for opening and closing:

What I tried was to saturate the tissue, run the coolers then mop up any condensed liquid on the cooler then re-seal the jar.

I don't see the purpose. There is already condensed alcohol on the tissue. Opening and closing will only disturb getting a relatively stable atmosphere of saturated/supersaturated vapor.

John

 

You can procure some americium from an old smoke detector. It'll be a decent source of alpha paritcles.

 

Agree completely on putting the source inside the chamber.

As for opening and closing:

I don't see the purpose. There is already condensed alcohol on the tissue. Opening and closing will only disturb getting a relatively stable atmosphere of saturated/supersaturated vapor.

John

I saw a note on u tube not to let the coolers swim in liquid so that's why I mopped it up.

I've just stripped the whole thing down and am re-building the cooler stacks with copper spreaders instead of aluminium. I'm going to use small heat sinks (cold sinks?) on the cold side inside the chamber. To remove the heat I will use two liquid filled pumped computer processor coolers on the hot side which have flexible pipes to enable the heat to be further removed from the cold side. I went to a local hardware store and got four ionisation smoke alarms for £10.00!!! bargain! Just as a note to anyone stacking peltier coolers, make sure to use the very best heat sink compound containing silver. An even thin coating is far better than too much, also, it is important to use an efficient spreader that covers the whole surface of the larger cooler, copper is by far the best reasonably priced material. Make sure both sides are completely flat with no burrs or warps. Make them about the same thickness as the cooler. By using good spreaders, you don't have to mount the second cooler in the center of the first one, I could detect NO difference in cooling when I experimented with copper, but with aluminium with it's higher thermal resistance, it is best to place them concentrically.


P.s. do not wire the coolers in series, use a separate adjustable power supply for each cooler. If the stated max current for the cooler is say 10 amps, start off at around HALF this current,remember that the cooler will be generating its own heat which also has to be removed.

 

I'm trying to make a cloud chamber to observe cosmic rays, alpha particles, etc. I don't want to use dry ice, I have tried cascaded peltier coolers on a very efficient fan cooled copper heat sink which easily reach -30 deg C. A piece of tissue wetted with 99.9% pure isopropyl alcohol is suspended with a magnet and a large washer either side of the top of the glass jar ( a large inverted coffee jar) So far I have not been able to form any mist, there does not appear to be any thermal gain between the warmer heat sink back to the cold side. The temperature is measured with a contact probe on the cooler. Total T.D is over 50 deg C between the hot/ cold side of the coolers. each cooler, 4 in total, (arranged as two in cascade, in parallel with another pair) have their own adjustable power supplies which have been set for maximum cooling at minimum current. I have tried several combinations of T.E.C's and the results are all similar. I did try water cooling the fins of the heat sink with only a marginal improvement of 3 deg colder. Still no mist, so anyone got any ideas?

Someone once described a cloud chamber to me, using a mixture of methylated spirit and another ingredient I can't remember.

The vapour is produced by pressurising the chamber and then decompressing it suddenly.

At a pinch - you could raise the pressure with a car tyre footpump, or even a bicycle pump. Then you just need an exhaust port you can release quickly.

Arranging a vacuum pump to reduce the chamber pressure abruptly would probably be expensive.