EarthTech's Fusor
Search for Recoil Proton Tracks in a Diffusion-Type Cloud Chamber - 22MAR99
A diffusion-type cloud chamber is a continuously active chamber developed by Langsdorf in 1939. A heated vapor source is located at the top of the chamber and the floor of the chamber is chilled significantly. A vertical temperature gradient will result and there will be a certain zone in which the vapor is sufficiently supersaturated that condensation will take place on ions.
This photo shows a diffusion-type cloud chamber mounted beside our fusor. The cloud chamber consists of a clear plastic container inverted over a black-painted Al plate, which is cooled from below by a slab of dry ice (pressed up against the plate with a piece of spring steel). A layer of felt has been glued into the bottom of the plastic container (which is on top now) and this felt is saturated with isopropyl alcohol to serve as the vapor source. It is heated simply by the ambient.
About 15-20 minutes after closing up the chamber and installing the dry ice, the chamber becomes active. For some reason, the active layer in this chamber is quite shallow, about 1/2" deep right at the bottom.
This chamber is sensitive to natural radiation. During a 10 minute period, I counted 7 tracks that were sufficiently long and distinct that I might be tempted to consider them recoil proton tracks had the fusor been running.
During another 10 minute period with the fusor running nearly continuously, I counted 45 such tracks!
Proton recoils from 2.5 MeV neutrons can have any energy from 0 to 2.5 MeV and the average should be about 1.25 MeV. A 1.25 Mev proton has a range of about 3 cm in air so we should expect tracks in the cloud chamber about that long.
This photo shows the bottom of the cloud chamber, under illumination from the side, with a millimeter ruler lying in it for scale. The major numbered divisions are centimeters.
Following are several photos of tracks that I think are made by recoil protons. By the way, the source of the protons is hydrogen atoms in either the black paint or the clear plastic container. In this photo the track is very dense and bright. It is about 2-3 cm long.
The next two photos (below) show longer, more diffuse tracks. If the proton gets the full 2.5 MeV, it can make a 10 cm track. Also, if the proton actually flies thru the chamber above the active layer, the ions it produces can drift downward into the active layer and create a diffuse-looking track.
This last photo (below) shows a thready little track (lower center) about 3 cm long. Apparently it originated in the black paint on the right and rose at a very slight angle as it progressed to the left. At the extreme left end of the track you can see the reflection of the track in the bottom of the chamber, which is quite reflective as it is covered with a layer of liquid alcohol. Other lines, which look a little like tracks in this photo, are just scratches on the plastic.
