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I was fascinated to read Steve Barrett’s article in JBAA V134.4 on the construction of an inexpensive cloud chamber and his images of proton, muon and electron tracks. Very impressive!
For only a little bit more expense and construction effort, a magnetic field could be imposed across the chamber. Either a couple of permanent magnets (though large ones are hard to come across these days since the demise of CRT televisions) or hand-wound Helmoltz coils would work well. Such would show very nicely the masses and charges of the passing particle.
Another design of particle detector is well within reach of home or school teacher constructors, though one would need to keep pupils’ fingers at a safe distance. This is a spark detector.
A frame work of insulating rods (perspex is the traditional material) forms a roughly 1 metre cube. At each few millimetres vertically, a row of thin uninsulated wires are stretched horizontally. Alternate layers run left-to-right and front-to back. One set, say the L-R, are grounded. The other layers (so F-B) are at a few kilovolts with respect to the first. HV power supplies are readily available, either from scrapped CRT monitors (essentially free), fly zappers which lure insects with UV light to exactly such a grid (~30 EUR/GBP/USD) or commercial HV PSUs (very expensive).
The voltage gradient, given by the voltage of the wires and their separation, is set so that the air is almost but not quite at breakdown voltage. The ionization caused by passing charged particles produces a very nice long trail and a satisfying *snap*. If you wish to get fancy, the noise could be used to trigger a camera, thereby saving on image storage space.
Such spark chambers work very well indeed, in my experience. In addition, a cubic metre is a much greater collecting volume than a jam jar. They also work for days, weeks or months without attention and need no re-fueling with IPA or the like. In particular, one could attempt to measure diurnal and seasonal variations in cosmic ray intensity.
Paul.
P.S. I had to replace my fly zapper recently because its UV LEDs died. I now have a surplus 4kV PSU …
Steve is a member of one of my societies (Bromsgrove AS). He gave a practical demonstration of his cloud chamber and particle tracks at a monthly meeting several months back. It is very impressive, and great fun to watch. He’s a top speaker too!
Gary
Is anyone building the cloud chamber described in the August Journal? I am having problems with the 12710 Peltier coolers sourced from the link in the cloud chamber paper? My two examples do not draw the 4 amps suggested, but only about the same as a 12706 cooler, around 2.5 amps.
There is an interesting little “Muon Telescope” project here using 4 Geiger detectors in a coincidence detecting array
http://parac.eu/projectmk30.htmCheers
RobinIt’s good fun watching the trails appear. We used recycled dry ice. The website won’t allow me to attach a video to show the trails.
I have built one but made a few modifications. I found that the 1 ohm resistor had to be increased to four ohms with a voltage of 10.5.
Pulls just over 6 amps and cools down to -22c with a room temperature of 25c
Have had to set it to one side for the moment but will work on it again soon.Attachments:
Having replaced the 12710 module with one from a different supplier, my chamber is performing well.
At 8.5 V with a 1 ohm resistor it reaches -25C in about 5 minutes, drawing around 7A.
My conclusion is that there are some mis-labelled modules out there.I have completely rebuilt mine with the main change being a liquid cooled heat sink. Before it would cool to -20c and then the temperature would slowly climb as the heatsink became saturated. With the new heatsink I now get -30c and it holds even with the voltage backed off.
Just need some IPA to see if vapour trails can be seen
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