Open source expansion cloud chamber

Visualizes tracks of ionizing particles

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An expansion cloud chamber works by saturating the air in a chamber with isopropyl alcohol vapor. Dropping the pressure in the chamber suddenly, causes super-saturation. Cloud will form wherever electric charges are. Unwanted charges in the chamber are eliminated by an electrostatic clearing field. Alcohol droplets then forms on the tracks of charge recently left by ionizing particles. An advantage of the expansion cloud chamber is, that you don't need try ice like for a diffusion cloud chamber. The disadvantage is that it is transient in operation. It only shows a snap-shot of the tracks and can only be operated a few times per minute.

The expansion cloud chamber was invented by Charles Thomson Rees Wilson (1869–1959) and he received the Nobel Prize in physics for it in 1927.

Original Wilson cloud chamber (source):

Beside many other applications, Wilson cloud chambers have been used for cosmic ray research. War-built V2 rocket with a nitrogen gas operated Wilson cloud chamber:

From July 1948 edition of Popular Science

Following figures show the general design of the expansion cloud chamber:

Additionally a high voltage power supply is needed. Next figure shows the schematic of a Villard cascade voltage multiplier. Please note, the transformer T1 is operated in the opposite way as usual.

The cloud chamber needs a fan-shaped light beam. Therefore a line laser is suitable. Several years ago I built a few cloud chambers and experimented with different light sources. A line laser provides a fan-shaped light beam and excellent visibility of the tracks due its spectrum. You can check out this video I made in 2010 to see an expansion cloud chamber with line laser illumination in action.


This project is released under the MIT license.

View all 9 components

  • Expansion chamber prototype

    M. Bindhammer07/24/2016 at 08:07 0 comments

    Here are some impressions of the prototype:

  • Radioactive sources

    M. Bindhammer05/31/2016 at 17:00 0 comments

    1. Uraninite

    Try to buy Uraninite (formerly pitchblende) at a mineral show. I bought some pieces of Uraninite from the famous formerly Russian uranium mine of Hartenstein, Saxony, Germany, at an internet mineral show. Uraninite contains up to 88% uranium. Uranium is weakly radioactive because all its isotopes are unstable. Below video shows the radiation measurement with a GAMMA-SCOUT Geiger counter.

    2. 241-Am

    The most common Americium isotope 241Am can be obtained from an ionization smoke alarm. The isotope has has a half-life of 432.2 years. 241Am decays mainly via alpha decay, with a weak gamma ray product:

    Next figure shows a dismantled Ei100L smoke alarm. The red, round structure at the right is the ionization chamber.

    The washer shaped part in the middle of the lower electrode of the ionization chamber contains the 241Am. It has an activity of 33kBq.

    Do not touch it directly! Always use tweezers or pliers. If alpha-emitting radionuclides do enter the body, alpha radiation is the most destructive form of ionizing radiation. A large enough dose can cause any or all of the symptoms of radiation poisoning.

    Trimmed 241Am source soldered onto the brass disc described here. Make sure, the alpha particle emitting side points to the center of the brass disc.

  • PCB design

    M. Bindhammer05/28/2016 at 13:28 0 comments

    First vision of the high voltage and laser power supply PCB:

    I didn't add ground planes due to the high voltage.

    Blank PCB:

    Populated PCB:






    C1, C2

    Electrolytic capacitor, 10μF, 63V, lead space 2.5mm



    Ceramic capacitor, 1μF, 16V, ±10%, 0805



    Electrolytic capacitor, 33μF, 63V, lead space 2.5mm



    Ceramic capacitor, 10nF, 16V, ±10%, 0805



    Ceramic capacitor, 100nF, 16V, ±10%, 0805



    Ceramic capacitor, 10nF, 16V, ±10%, 0805


    C8, C9, C10, C11, C12

    Ceramic capacitor, 100nF, 1000V, ±10%, 2220


    D1, D2, D3, D4, D5

    SM4007, DO-213AB



    DC power jack, PJ-202A



    Timer NE 555 D SMD, SO-8



    PCB mount screw terminal, 2 pins, lead space 3.5mm



    PCB toggle switch, 5236AB, lead space 4.7mm



    N-FET BUZ71, TO-220



    Resistor 12kΩ, 1%, 0.125W, 0805



    Resistor 4.7kΩ, 1%, 0.125, 0805



    PCB transformer, 6V/230V, 1VA



    800mA low-dropout linear regulator LM1117MPX-5.0, SOT-223



    1A low dropout regulator for 5V to 3.3V conversion LM3940IMP-3.3, SOT-223

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Enjoy this project?



lantramnamcodon wrote 07/20/2016 at 05:30 point

we should add the microwave module to there.and why don't we make some Natri-iodine vacuum?

  Are you sure? yes | no

lantramnamcodon wrote 06/22/2016 at 16:21 point

i every like some projects like this.i want to make an antiparticle sensor.i already hear about the diagram of it and i hope you will join with me.

  Are you sure? yes | no

M. Bindhammer wrote 07/23/2016 at 19:03 point

Sorry, dude, I do not know what you're talking about.

  Are you sure? yes | no

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