How to make a peltier cooled cloud chamber. No Dry Ice!

Part 5: Pictures, Videos and explanations.

These pages provide instructions on how to build the peltier cooled cloud chamber shown on my Youtube channel.

Part 1: Shopping list and some design considerations

Part 2: The electronics

Part 3: Assembly

Part 4: How to use

Part 5: Pictures, Videos and some explanations

Pictures    Videos    Explanations


  Good and bad lighting.



Lit from the side, 90 degrees from the viewing angle (ie from the left in shot).

Tracks are visible (barely) - in video the alcohol 'mist' is just about discernable. See videos.








In this pic' the illumination is from directly opposite the camera and parallel to the coldplate surface. The camera is angled down to view into the active zone with the light mask preventing the illumination from entering the camera lens.

The tracks are clearly visible as well as the alcohol mist. Fine tracks, even the odd rare Muon track, can be seen in the mist. See videos.

  Frost Garden


Water for fuel does produce tracks from the source but they are very faint. See videos

A 'frost garden' rapidly builds up - I put a bit of fine wire in the chamber to encourage a 'frost tree'.

The water 'fuel' rapidly cooled and stopped working after a few minutes - it froze.

The system needed to be thoroughly dried before re-use.

See video 


Particle from a piece of granite, impacts an air/fuel molecule and deflects 90 degrees spitting out debris 'backwards'?? - hmm.

  Alpha from the Am241 knocking off an electron(?) which also 'knocks out' another electron(?) - Inverted Y under small alpha track. see video
To view on Youtube click the links below:

Cloud chamber 1 - 1 short video of an Alpha source (Am241) and background

Cloud chamber with Water as the 'fuel' - water fuel, very quickly frosted up!

Poorly Lit cloud chamber- contrasting good and bad lighting!

Granite in a cloud chamber - some activity from a piece of granite.

Background radiation in a cloud chamber - just background radiation.


  Water fuel, -38C.

Wire for 'frost tree'.

Only worked for a few minutes before the water froze.

Very indistinct tracks against the glare from the frost.

  Poorly lit cloud chamber.

Light was at 90 degrees to the viewing angle, as described on most websites etc. The last few seconds is the same chamber, fuel etc but with the lighting and view angle I describe in these pages.

  Granite 'chunk'.

Small piece of granite placed on the perspex fence.

It's not particularly active, but it does emit an Alpha and some other radiation.

There is plenty of background radiation visible, so in the next video it is just looking at the background.

  Just background - could be scary if your unaware!!

This is 13 seconds of uncut, unedited raw 'footage' showing just background radiation. I live in the centre of town 30Km or more from a nuclear power plant and nowhere near any nuclear waste dumps (that we know of) - it's ALL background.

    Events - a small collection of interesting events.


1: It doesn't work!

2: Why 'look into the light.'

3: How cold can peltiers really go?

4: Why can we see radiation in a cloud chamber. 


Approximate values when running in 18C water - every system will be different:

Coldplate: -40C

Top peltier lowest temp: -40.1C

Temperature across peltier junction: less than 0.5C

Bottom peltier highest temp: +21C

Heatsink next to block: +20C

  It doesn't work:

First measure your peltier voltages and currents - ensure you have 5v on the top peltier and 12v on the bottom and the peltiers are the correct way up - check the wire colours.

If they are correctly powered and orientated remove the polystyrene base and use your temp' probe (cut a slit to work the probe into the foam pieces) and measure the temperature at the top of the heatsink, the spacer block, the hot and cold sides of both peltiers - you'll only get to the edge so careful probe positioning to ensure correct measurement.

If there is a significant difference (more than a degree or two) between any of the mating surfaces then the thermal contact is poor and you will need to dismantle the stack and re-build.

Apart from that - unless the insulation you have used is really abysmally bad or you have a faulty peltier - there is not a lot to go wrong.

If you suspect a faulty peltier. Dismantle the stack and carefully re-check the peltiers individually - without heatsinks at 5 v /1.9 Amps the hot and cold sides will be obvious within 1 second if the cell is working.

  2: Why 'look into the light?'

The droplets in the mist act like small spherical lenses. These will scatter light off their edges but all the light that enters the droplet will pass through and be focussed inside the droplet, or just above the reverse side depending upon the refractive index of the droplet material. This light then forms an approx' 30 degree cone after is passes through the focus point/droplet.

Ref:  http://stackexchange.moderatenerd.com/2013/05/11/focus-of-a-ball-lens/


How cold can peltiers go?

That is n open question: 1 peltier, 2 in a stack, a multistage cascade, run in parallel, so many combinations.

To keep it simple this section describes 1 and 2 cell (1206) peltier stacks. These are the most common for this sort of project - and by far the lowest price!

The calculation of the potential cooling of a peltier system does require some complex maths to be accurate - I will keep it simple, just construction lines on a graph. This results in an estimate of the potential cooling. Note: as a peltier cell is cooled it will draw more current for a particular voltage and become less efficient at pumping the heat.

Reference to the manufacturers data sheets with power/voltage/current curves is essential.

Manufacturers application notes can be found here:    http://docs-europe.electrocomponents.com/webdocs/007b/0900766b8007ba20.pdf

Note: The Melcor CP 1.4-127-06 L - graphs below -This is their near equivalent of the readily available and cheap '1206'.


These graphs show the system with a hot side temperature (Th) of 25C. This would be typical for a good air cooled system, with watercooling the Th is down as low as you can go: Th -5.5C or so in my lowest temp' run.

The change in current with Th can be calculated, see Melcor datasheet page 19.

But there is no real need as we are not making a precision device. We just want it cold and estimate how cold.

One peltier running at 12 volts will pass about 5 amps when the temperature difference between the hot and cold sides is 40C (Td). At that temp' difference (40C) and 5 amps the peltier can 'pump' about 18 watts (red dashed lines).

If the peltier was pumping only 10 watts the temperature difference (Td) would be about 52C with 12V/5A. (blue dashed lines).

At zero watts pumped the Td would be 66C or so -  however to be pumping zero watts is not possible, leakage through the dome, insulation etc will be several watts.

So one peltier cell can reasonably expect to pump 10 watts at 12 volts and just under 5 amps - (the current reduces as the Td increases, see graphs) with Td = 50C or thereabouts.

If your Th is over 22C then the system would struggle to drop below the transition temperature of -26...28C .

We want colder:

Add a second (cold) peltier. 5 volts is so conveniently available so lets work on that, current lines for 5 volts are estimates:

5 volts results in approx' 1.8 amps at a Td of 20C. 1.8 amps x 5 volts = 9 watts.

If we estimate that the cooling load (Pc) is 10 watts then at 5v/1.8A the peltier would generate a Td of about 22C. (yellow dashed lines)

So the first peltier must now pump the Pc PLUS the 9 watts from the 2nd peltier power supply - say a total of 20 Watts.

This results in a Td for the hot peltier of 38C. (green dashed lines)

Therefore adding the Td of cold peltier (22C) and the Td of the hot peltier (38C) we get a result of a Total Td of 60C (at Pc of 10 watts).

ie at a hotside temp' of +22C the coldside should be about -38C at a heating load of 10 watts or less. A good temperature for a sensitive zone.


The minimum temperature that can be achieved in one of these systems is therefore very much dependant upon the heat leaking into the cold zone. This can be reduced with extra insulation and running the chamber when the air temperature and humidity are at their lowest - frosty winter pre-dawn outside is good, if your sufficiently hardy.

However as long as the coldplate gets below -28C or so the cloud chamber should work.

Image right of my system running at -58.5C coldplate temperature. 'Teacosy' of metalised polystyrene insulation, foam plug for top access to heat fuel source. Water (brine) is cooled to well below -10C, frosty bucket. Hot temperature probe is measuring the top of the heatsink as close to the hot peltier as possible @ -5.5C.

  Why can we see the radiation in a cloud chamber?

Radiation (specifically ionising radiation) when it passes through any substance knocks electrons off the atoms it interacts with. This causes these atoms to become positively charged ions.

If a gas (air) is saturated with a dissolved liquid (the fuel, eg isopropyl alcohol) and cooled so the air is 'supersaturated' the dissolved liquid will want to condense. Condensation normally occurs on dust particles and free ions present in the air. The optional use of an ion scrubber helps 'clear the air' of these natural condensation nuclei.

When the radiation particle passes through the air it leaves a trail of ionised gas (air) atoms/molecules in its wake. The liquid dissolved in the air rapidly condenses on this trail of ions making them visible.

The more powerful the ionised 'wake' the denser the 'cloud' of droplets formed.

Sketch to left is not to scale!

  Alpha radiation interact strongly with the air, and anything else it impacts. They are positively charged helium nuclei (2 neutrons and 2 protons) so relatively heavy. They 'dump' their energy very quickly leaving very strong 'trails' in the cloud chamber.
  Beta radiation is an electron. This is negatively charged and a tiny fraction (less than 1/1000th) of the mass of an alpha particle. These interact less strongly with materials, and tend to 'bounce around' in air leaving thin erratic tracks. They have a longer range than alpha particles and are more penetrating.
  Gamma radiation. This can interact strongly with materials and is deeply penetrating, depending upon the energy cm or metres of concrete. Gamma radiation would leave a thin straight line of ions in it's wake.
I have no pictures of anything I can be fairly sure is a muon.   Muons. These only interact slightly with materials. They are created when high energy cosmic rays hit the upper atmosphere and cause a cascade of particles to rain down. Ref: http://en.wikipedia.org/wiki/Cosmic_ray

Muon tracks are hard to see in a peltier cloud chamber since most are coming straight down so will only pass through the thinnest direction of the sensitive zone.

Part 1: Shopping list and some design considerations

Part 2: The electronics

Part 3: Assembly

Part 4: How to use

Part 5: Pictures, Videos and some explanations



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Cloud chamber 1 - 1 short video of an Alpha source (Am241) and background radiation in a homemade peltier cooled cloud chamber without dry ice.

Cloud chamber with Water as the 'fuel' - a short video demonstrating water as active vapour, very quickly frosted up! How to make a cloud chamber without dry ice.

Poorly Lit homemade cloud chamber- contrasting good and bad lighting in my homemade peltier cloud chamber! No dry ice.

Granite in a cloud chamber - no dry ice - some activity from a piece of granite. No dry ice, peltier cooled.

Background radiation in a peltier cloud chamber - no active sources anywhere near, just background radiation. Peltier cooled, homemade cloud chamber not using dry ice.

How to make a cloud chamber - a 5 minute video on how to build a simple cloud chamber in less than an hour. How to build a cloud chamber without dry ice, peltier cooled.