YOU CAN BUILD A MACHINE THAT MAKES RADIOACTIVITY VISIBLE - LABS PAY 2,600 DOLLARS FOR THEIRS
A desktop instrument that makes individual particles of radiation visible as white vapor trails, built from CPU cooling hardware and isopropyl alcohol for under 100 dollars.
by Curious Scientist
ScienceWorkshop
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- ●●●○○
- time
- a weekend
- license
- license not specified
- repo
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●●●○○ · a weekend · license not specified · 0 stars · repo
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COMPAREE VERDICT
A cloud chamber is one of the most direct physics demonstrations you can build: you watch individual alpha and beta particles draw trails through supersaturated alcohol vapor, the same principle that won C.T.R. Wilson the 1927 Nobel Prize. Curious Scientist's build uses stacked Peltier coolers on a CPU water-cooling loop to chill the chamber floor to about -30°C, creating the temperature gradient needed for tracks to form. His blog post walks through the assembly with photos and a parts list that comes in under 100 dollars if you source carefully. Frank Prins documented a more refined version with printable enclosure parts and a complete BOM that runs closer to EUR 500, released as CC0. Both builds work, both show live footage of tracks, and both are missing the same thing: a proper wiring diagram. You will be reverse-engineering the high-voltage grid (usually from a bug zapper) and the Peltier power supply from photos and text. The single hardest part is not the assembly — it is getting the vapor density right, which takes trial runs with different alcohol volumes and temperatures. If you have never stacked Peltiers or tuned a supersaturated vapor, budget an extra evening. The reward is an instrument that makes the invisible visible, live, on your desk.
IN THE REPO
NOT IN THE REPO
- —Curious Scientist's blog post shows the build process with photos and a parts list, but no CAD files or technical drawings.
- —Frank Prins's alternative build includes a detailed BOM (~EUR 500) and STL files for 3D-printed parts, licensed CC0 (public domain).
- —Both builds document Peltier stacking, cooling loop assembly, and voltage supply setup. Neither provides circuit diagrams.
- —The radioactive sources shown (americium smoke detector element, thorium mineral) are legal check sources in most jurisdictions, but sourcing rules vary by country.
- —No firmware or code — this is a purely physical instrument.
- —Commercial lab chambers (e.g. PHYWE) cost around $2,600; both documented DIY versions come in well below $500 including all parts.
Can I build this?
Build at your own risk. Projects involve tools, electronics and sometimes mains voltage — follow the creator’s safety notes.
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Videos
Curious Scientist's video shows the chamber running with visible tracks from a thorium source. No spoken walkthrough, but live footage of the instrument in operation.
Gallery
Start here
Navigation into the creator’s own docs — we don’t rewrite the guide, we route you to the source.
- 1.Read both build guides (Curious Scientist's post is the $100 version. Frank Prins's post (prinsfrank.nl) is the refined EUR 500 version with printables. Pick one based on your budget and whether you want to 3D print an enclosure.)
- 2.Source the Peltier modules and cooling loop first(These are the long-lead items. TEC1-12706 modules are common, but check the wattage and voltage match your power supply. A used CPU all-in-one cooler (120mm radiator) works if it still holds pressure.)
- 3.Verify local legality of radioactive check sources before buying(Americium-241 from ionization smoke detectors and thorium minerals (e.g. from geology suppliers) are legal in many places, but rules vary. Research your jurisdiction before ordering.)
- 4.Test the Peltier stack on the bench before final assembly(Wire the modules in series or parallel (depending on your power supply voltage), apply thermal paste, mount to a heatsink, and verify you get sub-zero temperatures with a thermometer. Reverse polarity will heat instead of cool.)
Resources
Documentation, files and community threads for this build — we link straight to the original sources and never rehost the creator’s files.
KNOWN ISSUES
- Peltier polarity: wiring them backwards turns them into heaters. Test on the bench with a thermometer before sealing the chamber.
- Vapor tuning takes multiple tries. Too little alcohol and no tracks form; too much and the chamber fogs opaque. Start with the volumes in the blog posts and adjust from there.
- High-voltage bug zapper boards are not standardized. The one you buy may have different mounting holes or output voltage than the one in the photos. Plan to improvise the enclosure or grid mount.
- Water-cooling loops can leak. Test the pump and radiator assembly outside the final enclosure with plain water before committing to the chamber build.
- Radioactive source strength varies. A weak source (old americium button, low-activity mineral) will show fewer tracks. If you see nothing after an hour, the source may be too weak or the vapor density wrong.
- The chamber floor (black felt soaked in alcohol) must stay very cold. If the Peltier stack cannot pull the floor below -25°C, tracks will be faint or absent. Verify temperatures before blaming the source.
Is this safe to run indoors?
Yes, with normal precautions. The radioactive sources shown emit alpha and beta particles that travel only millimeters in air and are stopped by the chamber walls. The high-voltage grid is low-current and enclosed. The main hazard is isopropyl vapor during assembly and refilling — do that in a ventilated space away from ignition sources. During operation the chamber is sealed.
Can I use a different cooling method instead of Peltiers?
Dry ice works and is simpler (no power supply, no stacking), but it is consumable and you need a source. Peltiers let you run the chamber continuously without resupply. Liquid nitrogen is overkill and adds handling complexity.
What am I actually seeing in the vapor?
Alpha particles (helium nuclei) leave thick, short tracks. Beta particles (electrons) leave thin, erratic tracks. Cosmic ray muons occasionally leave long, straight trails. You cannot see gamma rays directly because they do not ionize the vapor strongly enough.
How long does the alcohol last?
The felt floor holds a few milliliters and that evaporates over hours. You will refill every few sessions. Keep a squeeze bottle of 99% isopropyl nearby.
Can I use this to measure radiation levels?
No. A cloud chamber is qualitative — it shows that radiation is present and lets you see particle types, but it does not count rate or dose. For quantitative measurement you need a Geiger counter or scintillation detector.
Community builds
No community builds yet — be the first, we feature the best ones.
Discussion1
FROM THE COMPAREE TEAM
Both builds show live tracks from thorium minerals and americium sources, and neither required a clean room or lab-grade parts. What would you point yours at first — a vintage watch dial, a piece of uranium glass, or just cosmic rays?
Curious Scientist
Curious Scientist documents electronics and physics builds on his blog and YouTube channel, with a focus on instruments that make invisible phenomena visible. His Peltier cloud chamber was built as a demonstration of accessible physics hardware. Frank Prins's CC0 alternative build refined the design with printable parts and a detailed BOM.
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DISCLAIMER
- Comparee is not the author of the projects featured here. All rights to each project belong to its creator — every page links to the original source, and we never host creators’ files.
- Information is provided without warranty and may become outdated as projects evolve. Prices are indicative bands only — always check the creator’s parts list for current costs.
- Building and operating any project is at your own responsibility. Protective equipment, safe workshop practice and compliance with local regulations are the builder’s responsibility.
CompareeTEAM3d agoedited
Practical notes from our verification: both the Curious Scientist and Frank Prins builds are documented on personal blogs, not in a repository — the files are there, but scattered across blog posts and photo captions rather than in a single archive. The Curious Scientist video (giRq-82LA08) shows the chamber running but has no voiceover; all the learning happens in the blog text. The single biggest variable is not the hardware — it is tuning the alcohol vapor density, which takes trial runs and is barely mentioned in either guide. If you have never run a Peltier below -20°C or worked with supersaturated vapor, budget an extra evening for iteration. The high-voltage grid improves track sharpness but is not strictly required; you can see faint tracks without it if your vapor is dense enough.