Thermoelectric diffusion cloud chamber

Welcome to this page which will give you some technical informations about the Cloudylabs Cloud Chamber !



The LCD screen shows the temperature of the cooling liquid. The switchs control the lighting and the high voltage. The interaction surface is white due to the crystallisation of  humidity of air on the cold surface : if we put alcohol, we will see some particles

Back of the machine. Only a power plug is needed. High voltage, lighting, cooling system, NdFeB magnet (optional) are inside the machine. Only alcohol is needed to view the particles


How it works 

8 high performance thermoelectric cooler are put on a heat exchanger. The Peltiers are cools by water which flows in the exchanger and the energy is released in radiators with fans. The watercooling system is a closed loop, so there is no waste of water.

The high voltage is provided by a multiplier circuit (2 outputs are available 1500 and 2500V, which are choosen depending the observations conditions). The next picture shows the difference with or without electric field in the chamber : it serve to have thinier condensation trails.


Left : no electric field. Right : Electric field is ON


Intensity and potential of the high voltage. The current is circuit-limited at 50 uA  (a 2M resistor is also present to strengthen the security)


Features of the Cloudylabs cloud chamber

Magnetic field

A cloud chamber without magnetic field shows little interest. This one was built to put a strong magnetic field in the interaction surface. The Lorentz force will deflect the lightly charged particles, such as electron and positon, according to their charges (electron will deflect to left and positon to right, but this depend on the direction of magnetic field !). The particles will describe « circles » where R is the radius of curvature. By mesuring R, you can rougly estimate the energy of the particle as you know it’s mass and the intensity of the magnetic field (R=mv/Bq and E=m02c4+p2c2).

The magnetic field is useful to detect the gamma annihilitation process (or pair creation). Without magnetic field, it’s impossible to say that we are looking at 2 differently charged particle (remenber that the pair creation process occurs only when the energy of the gamma is at last of 1.02 MeV, cosmic radiations will provide this energy). The next picture, taken in the cloud chamber, show what a pair creation look likes.

Left : an alpha particle is not subject to the magnetic field because this particle is too heavy to be deflected by the present field, but the electron is deflected (if they have energy < 1MeV which is often the case). Magnetic field can also discriminate muons from electron : Muons are 207 times heavier than electron so they are not subject to deflection (only if they have very low energy). Right : pair creation (gamma annihilation)

The magnetic field is provided in the chamber with a Neodymium magnet which can have the maximum size (inch) of : 2.75″x6.5″ thickness 1.75″.

Location of the magnet in the chamber (under the interaction surface, without disturbing it). Example of magnet used for the previous picture (4″x2″x1″). In the chamber the intensity of the magnetic field is about 140 mT with this magnet



Glass chamber, lighting

The walls of the chamber are in glass which is scratchproof and easily cleanable (the electric field tends to attire dust). The density is heavier than plastic so there is (a little!) more chance to observe spallation from neutron or proton interacting in the wall. I observed this elastic proton-proton scattering years ago in a V2 air cooled cloud chamber (see below).

Elastic proton scattering. Click for more !

The lighting is provided by 80 leds (cold emission spectrum) to have an homogeneous illumination. It’s possible so switch off the lighting to show the fluorescence of radioactive sources like radium, tritium, autunite or uranium oxydes.

2 connections (lighting and high voltage) needs to be plugged when the experience begin.

This is the top of the chamber where you can put alcohol (about 2 mL can run the experience for 30 minutes, see the next movie for example)

Size of the machine

About the volume of a laptop computer. Dimension of the chamber is 16.5″ x 13.5″, Height : 13″. The electrical power is 650W at 220V.


Summary of functions

Storage and handling of the machine with it’s custom box (4 truckles are present)


  • Comfort of use : No need of dry ice or external system (tap water for example). A 220V power plug is only needed (it’s possible to make a 110V input on request). The 8 thermoelectric elements can reveal the particles in 30 seconds-1 min after turning on the machine. The active area is 16 x 8 cm (6.3″x 3.1″). All the other thermoelectric cloud chamber available on internet needs at last 10 min to show the first particles because they use few thermolectric elements and are cooled by air which is less efficient than water.
  • Building :  It’s easy to put any type of radioactive source in the chamber. You can add a Neodymium magnet which will provide a strong magnetic field because the magnet is only 1 inch away from the interaction surface ! The glass chamber is perfect for photography or retransmission of the events with a camera. You can see the particles from the top of the chamber.  The operation of maintenances (each machine need one) are easy because all the part are accessible. All electrical circuit are simplified to maximum to avoid the risk of failure with time.
  • Originality : Conceived and built by an ardent-passionate lover of cloud chamber for 4 years, after seeing a big one (a Phywe PJ45, 25.000€) in action during my nuclear studies at University.

Some drawbacks :

  • After few weeks of use, the thermal pastes on the interfaces need to be changed for a fresh one. Thermal paste is supplied in quantity with the machine. Check montly if there is enough cooling liquid in the pump tank.

  • The quality of observation and rapidity of etablisment of the equilibrium depend on your environment : avoid dusty place, wind stream, or warm room (>30°C).


Availability :/


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