Make a Cloud Chamber using Peltier Coolers

Cloud chambers let you see vapor trails left by radioactive particles!

A version of this cloud chamber is now available for purchase (fully assembled and tested) from

Discuss cloud chamber assembly and radioactive samples at

Cloud chambers work by creating a supersaturation of alcohol vapor. Vapor trails are then formed when the radiation ionizes the alcohol.

Cloud chambers need to be very cold (about -15f) - so most designs require dry ice.

This design uses inexpensive electrical "Peltier" coolers instead! No need to buy / store dry ice!

It's fairly easy to construct - and should only cost about $100.

This chamber design cools down very quickly - you can see vapor trails within a few minutes.

On the downside - it's not as cold as a dry ice chamber - so the supersaturated area isn't as thick.

Step 1: Stuff You'll Need (Part 1)

Make a Cloud Chamber using Peltier Coolers
Make a Cloud Chamber using Peltier Coolers
Make a Cloud Chamber using Peltier Coolers
Peltier Coolers (need 2)
- Model 12709 (138 watts "max") for "top" cooler ($8 on ebay)
- Model 12710 (168 watts "max") for "bottom" cooler (also $8 on ebay)
- Search eBay -descriptions- to find specific models
- Often listed as "TEC", "Thermoelectric" or "Peltier" coolers and have TEC1 or CP1 as a prefix to the model number
- Other models with similar wattage ratings can likely be used (bottom cooler should have a slightly higher wattage rating than the bottom)
- Coolers look identical - put a piece of tape on a wire of the 12710 so you can identify it later
- Larger coolers are not necessarily better
- Fragile wires tend to break - avoid bending (might want to buy a spare or two)
- Do -NOT- connect a peltier to power backwards or without a heatsink!
- See the bottom of this page for info on a single-Peltier option

Power Supply #1
- 12v and at least 8 amps (good results between about 11v and 15v)
- Used to power 'bottom' peltier cooler
- part # PS-1512 is a good option for $25

Power Supply #2
- 5 volts and at least 2.5 amps (good results between about 4v and 8v)
- Used to power 'top' peltier cooler
- D-Link JTA0302C power supply on ebay for about $10
- Alternative: Use a PC ATX power supply for both 12v and 5v sources (Google for more info)

CPU Cooler / Fan
- Look for "heat pipes" and a 120mm fan
- Design that can be run "upside down" with good airflow
- The Cooler Master Hyper 212 works well and is cheap (under $30 on ebay)
- Cooler Master V8 works well and looks cool (about $50)
- The Corsair H50 (liquid cooling) works a little better - but is more expensive / complicated (about $70)
- See for other possible coolers

Alternative Single Peltier / Single Power Supply Configuration
- This project can also be built using a single dual-stage peltier cooler
- The 19012-5L31-06CQQ from Custom Thermoelectric ($53) has been tested and works well (order with Moisture Sealing option)
- Requires a 12V power supply capable of 6 amps (5V power supply is not needed)
- Other project details stay the same

Step 2: Stuff You'll Need (Part 2)

Make a Cloud Chamber using Peltier Coolers
Make a Cloud Chamber using Peltier Coolers
Make a Cloud Chamber using Peltier Coolers
Small Plastic Container
- Relatively flat bottom (doesn't need to be perfect)
- Fairly thin plastic (1/16th" or less)
- Good Transparency
- Good results with Rubbermaid Premier 473ml (about $5)

Arctic Silver 5 Thermal Compound
- $10 at Radio Shack for 3.5 grams
- Should probably get 2 tubes (if you're efficient you may get away with 1)
- Arctic Silver "Ceramique" provides good results for less money (22 grams for about $10 at Fry's)
- Other thermal compounds / paste can work
- Have -not- had good luck with Radio Shack's "house brand" thermal paste

- 99% rubbing (isopropyl) alcohol works best ($5 at drug store)
- Denatured ethyl alcohol is another option (hardware store paint section)
- 91% rubbing alcohol can also work (maybe not as well)

Misc. electrical connectors to hook stuff up
- Soldering is another option
- Don't use thin-wired gator clips - they'll melt

LED flashlight (the cheap 9-LED ones work well)

Black Sharpie felt pen

Step 3: Stuff You'll Need (Part 3)

Make a Cloud Chamber using Peltier Coolers
1/4" x 1" nut + bolt (size doesn't really matter)

1" x 1" piece of kitchen sponge

Styrofoam cup (or other static source - a balloon also work well)

Infrared / non-contact thermometer (optional)
- Optimally can read to at least -28f
- Cen-tech Pocket Thermometer goes for about $20 on ebay
- Cheaper ones may give erratic results

Multimeter (optional)
- For verifying power supply polarity / troubleshooting

Step 4: Obtaining a Radioactive Source

Make a Cloud Chamber using Peltier Coolers
There are many easily obtained inexpensive (and legal) radioactive sources available online.

See video samples / discuss radioactive sources at

Certain years of Fiestaware dishes featured a "radioactive red" color that actually contained uranium!

A small chip can make an excellent cheap cloud chamber source - try searching ebay for "fiestaware sample"

Small Autunite samples commonly sell for about $20 on ebay (contains uranium).

Search ebay descriptions for "geiger" and "cpm" to see other possibilities.

Alternately - the cloud chamber can be used without a radiation source to view cosmic rays. They typically appear once every 1-2 minutes.

Take precautions appropriate for your sample! The provider of your specimen may be able to provide further information on its safety.

To be extra safe - use gloves when handling. Wash your hands after if you should touch it.

Step 5: Add Thermal Paste to the Heatsink

Make a Cloud Chamber using Peltier Coolers
Position the CPU cooler with the heatsink surface facing up.

Spread a small amount of Arctic Silver on top of the heatsink using a credit card or thin piece of plastic.

Spread it thinly and evenly (thinner is better). Cover an area the size of a peltier cooler.

Step 6: Mount the Bottom Peltier Cooler

Make a Cloud Chamber using Peltier Coolers
Place the 12710 peltier cooler on top of the heatsink.

Important: The wires should be facing you and the red wire should be on your right.

This should assure that the peltier is positioned with the cold side up.

Push the peltier down - and move it around slightly to assure good contact with the thermal paste.

Step 7: Connect the Bottom Peltier and Fan to Power

Make a Cloud Chamber using Peltier Coolers
First - Make sure the 12v power supply is unplugged!

Electrically connect the CPU cooler's fan and the peltier to the 12v power supply.

Red goes to positive, black to negative.

Ignore any unused connections for the fan.

Step 8: Test the Fan and Bottom Peltier

Make a Cloud Chamber using Peltier Coolers
These steps need to be performed quickly! If the peltier is connected backwards or is upside down - it'll burn up in a very short period unless it's disconnected.

1. Plug in the 12v power supply (fan should spin up)

2. Quickly touch the top of the peltier (or measure it with a thermometer)

3. Is it warm? UNPLUG THE POWER NOW! (peltier is backwards or upside down)

4. Is it cold? Good! (unplug the power)

Step 9: Spread Thermal Paste, Attach the Second Peltier and Connect it

Make a Cloud Chamber using Peltier Coolers
Thinly spread a small amount of Arctic Silver over the top of the peltier you've already placed on the heatsink.

Place the other peltier (12709) on top of the existing one. Push it down a bit to assure good contact.

Important: The wires should be facing you and the red wire should be on your right.

Connect the top peltier to the 5v power supply (leave power supply unplugged).

Step 10: Test the Top Peltier

Make a Cloud Chamber using Peltier Coolers
Same drill as before - these steps need to be performed quickly!

1. Plug in the 5v power supply

2. Quickly touch the top of the peltier (or measure it with a thermometer)

3. Is it warm? UNPLUG THE POWER NOW! (peltier is backwards or upside down)

4. Is it cold? Good! (unplug the power)

Step 11: Test Both Peltiers Simultaneously

Make a Cloud Chamber using Peltier Coolers
Plug in the 5v and 12v power supplies.

Marvel at how cold the top peltier gets!

If you have a thermometer - hopefully it reads -18f or colder!

If not - something might be wrong - or it could just be your thermometer isn't that accurate (this is common).

Unplug both power supplies. If any condensation has formed on the top peltier - wipe it off.

Step 12: Black Out the Bottom of the Cloud Chamber

Make a Cloud Chamber using Peltier Coolers
Use the Sharpie to black out the -outside- bottom of the plastic container.

This will help the vapor trails appear more clearly.

Step 13: Attach the Sponge to the Container's Top

Drill a hole in the top of the container for the bolt.

Poke a small hole in the sponge using a pencil.

Use the nut and bolt to attach the sponge to the inside top of the container.

Don't worry about the seal not being perfect. A small leak at the top of the chamber won't hurt performance.

Step 14: Apply Thermal Compound to the Top Peltier

Make a Cloud Chamber using Peltier Coolers
Apply Arctic Silver to the top of the top peltier.

This time - apply it fairly liberally. Use enough so that good contact can be made with the bottom of the container (accounting for any imperfections like raised text).

Yes - normally less is better with thermal paste - but this is an exception.

This may be the point where you have to run to Radio Shack to buy another tube of Arctic Silver.

Step 15: Attach the Container to the Top Peltier Cooler

Make a Cloud Chamber using Peltier Coolers
Place the container on top of the top peltier. Push it down - and squish things around a little.

If it doesn't seem to be making good contact - try adding more Arctic Silver.

Try to make a tight seal - you don't want condensation getting between the container and the peltier.

Step 16: Test Everything with Container Attached / Troubleshooting

Make a Cloud Chamber using Peltier Coolers
Plug both power supplies in.

The bottom of the container should get very could within several minutes minutes.

If you have a thermometer - hopefully it reads -14f or better! (Don't worry if the entire surface doesn't read this cold.)

If so - your cloud chamber is now ready for use!

If you aren't getting this cold:

- Don't place too much faith in your thermometer - if you're getting significantly below 0f - it may make sense to proceed and see if things work

- This article originally suggested Tec1-12709's top and bottom - this will work - but using a Tec1-12710 on the bottom works better. If you're using two Tec1-12709's and having poor results - you may want to switch out the bottom one with the CP1-12710.

- Check your thermal paste application - this is probably the most common issue. The layers between the peltiers and the heatsink should be thin. The final layer between the top peltier and the chamber may need to be fairly thick to make good contact. As a last resort - you may find that removing all thermal paste using alcohol - and then re-applying solves the issue.

- Are the peltier coolers and container all centered over the middle of the heatsink?

- Is your heatsink getting even a little warm? If so - it may not be good enough.

- If your heatsink is getting warm - one option is to remove the fan - and place it in a container of cold water (maybe even with ice). This will provide extremely effective cooling - at least until the water warms up.

- Verify your electrical connections are good (warm wires indicate they are too thin).

- Try applying a small amount of weight / pressure to the top of the chamber - this might help close up any gaps in the thermal paste.

- Re-test the peltiers. You can also check them against their specified resistance values using your multimeter (they shouldn't read any higher than 4 ohms).

- Try waiting a few hours - some thermal pastes will "set up" and become more conductive over time

Step 17: Using the Chamber

Make a Cloud Chamber using Peltier Coolers
Make a Cloud Chamber using Peltier Coolers
Place your radioactive sample inside the cloud chamber.

Add about 1 teaspoon of alcohol to the sponge.

Put the top on the container.

Plug in both power supplies.

Hold the LED flashlight behind the chamber.

Within a minute or two you should be able to see a fine mist covering the bottom 1/8th inch or so of the container.

Try changing your viewing angle / flashlight position to best see the mist.

Rub the styrofoam cup (or other static thingy such as a balloon) in your hair - then place it over the container.

Within 2-10 minutes - you should start seeing vapor trails from the radiation!

IMPORTANT: "Recharge" the styofoam cup / balloon (rubbing it in your hair) periodically. Try removing it / repositioning it to see what provides the best visibility of radiation trails. This is key to being able to see alpha particles!

If you don't see trails - revisit the troubleshooting section in step 16.

Performance may improve as things cool.

Step 18: Tips

Make a Cloud Chamber using Peltier Coolers
Important: Periodically check to make sure the peltiers / chamber aren't sliding away from the center of the heatsink (this is bad). Gently reposition them if this happens.

Without a radiation source - you'll be able to see cosmic rays every few minutes. Definitely try this!

Get help / share your cloud chamber with others at

It's possible to run the chamber with the top slightly off (or with a hole cut in it) for direct viewing. This can be great for shooting photos and video.

If you're not getting trails - or they seem to vanish quickly - try re-applying a static source (styrofoam cup / etc) as mentioned in the prior step. This is key to getting good results!

If you like playing with high voltage - you can try attaching a 1kv or higher DC source to the screw on top of the chamber. This will provide the same ion-clearing / performance-boosting effect the styrofoam cup does - but is way cooler because it's high voltage.

If too much alcohol builds up on the bottom of the container - it may hurt performance (wick it up with a paper towel).

If your sample becomes wet with alcohol - some radiation will get blocked (again - a paper towel can solve this issue). This is a very common issue with small Americium samples.

The rubbing alcohol on the sponge should last a long time - but if you stop seeing trails - it may be time to add more.

If you only see trails / mist over a small portion of the container - you may want to try applying more thermal paste between the container and top peltier.

Other directional light sources besides LEDs (like spotlights) can also provide good lighting results. Standard incandescent or florescent bulbs may even work at certain angles (especially if in a desk lamp or other fixture)- experiment!

To improve viewing contrast - black out the -inside- of the container with the black permanent marker. The downside of this is that eventually the alcohol will dissolve the ink - making a bit of a mess.

Depending on a number of variables you may find that increasing / decreasing the voltage for either cooler may improve results.

However - do -not- try running the top peltier at 12v instead of 5v. It won't work (at least not well) - trust me.

(The quick explanation is that each peltier needs to pump all the heat pumped by the one above it -plus- any heat the upper peltier generated itself. Since peltiers are not very efficient - this head adds up pretty quickly - and becomes a problem. Trying to stack two peltiers running at the same total power level will result in -less- cooling than a single peltier at the same power.)


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