In this video I'll attempt to build a Cloud Chamber for visualizing subatomic particle trails. These particles come primarily from cosmic rays, which is ambient radiation from outer space. The three main sources of radiation we'll see here are Alpha particles (relatively slow but massive helium nuclei), Beta particles (very fast electrons, but much lower mass than Alpha particles), and Gamma rays (an ultra high energy photon with frequencies in excess of 10^19 Hz, which is about 100,000x the frequency of visible light).

In the chamber, alcohol evaporates from either a reservoir, or more commonly, a fibrous object with large surface area like a sponge / towel. The vapor pressure of the alcohol inside the chamber reaches saturation (like 100% humidity, but with alcohol vapor). When a plate at the bottom of the chamber is cooled, it drives the vapor below the its condensation temperature (same thing as moist air hitting the dew point). However, when this happens, the vapor doesn't immediately condense because it needs a nucleation site, so it's in a semi-unstable state where the moment it contacts something, it'll condense. When a high energy particle flies through, it smashes into the alcohol molecules, creating a nucleation site along its flight path. This leaves behind condensation trails, similiar to a jet aircraft. If the trails are illuminated with an intense light source against a black background, they can be clearly seen with the naked eye.

Alpha particles show up as short, fat trails. Beta particles show as thin lines that often have a dashed/dotted appearance, and Gamma Rays / X Rays show up as thin squiggly lines. Also, the paths of Alpha and Beta particles can be influenced by a magnetic field because they're charged. The charge/mass ratio of the Alpha is too low to cause any noticable deflection, but with a strong enough field, a beta particle can be steered into a spiral path. Unfortunately, I wasn't able to do this in my build, even with a large N52 magnet.

The most dramatic displays occur when a piece of radioactive material is placed in the chamber. In this video, I used an old camera lens containing Thorium-232 as a radiation source.

For this chamber, the plate is cooled to about -25C with a vapor compression system. The compressor, condenser, and filter/dryer come from a used icemaker i bought off eBay for $40, emptied, and backfilled with propane from my grill. The evaporator is a coil of 1/4" copper tubing thermally anchored to an aluminum plate with silicone. With the condenser fan, the whole system uses about 1.6A at 115V, or 172W. This is dramatically more powerful, efficient, and reliable than a peltier cooler based system, but requires some basic brazing and a vacuum pump to empty the refrigerant lines. For alcohol, I use 99% Isopropyl, but Ethanol or Methanol can also be used. I tried acetone for its lower boiling point, but it never produced any visible particle trails.

The application of a vertical electric field with several thousand volts will "sharpen" the picture of the trails by "flushing" residual ions out of the fog layer. However, mine wasn't very effective, probably because I only used a loop around the chamber walls instead of a grid covering the entire upper surface.

Music Used:
Kevin MacLeod - Lobby Time
Serge Pavkin - Cosmic Glow


I also have a patreon now if you want to help support the channel. This makes it a lot easier for me to buy parts and equipment for these projects:

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