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Devices used for the experiments
Own produced cloud chamber
The best ways to illustrate atomic tests are the particle detectors. We built the diffusion cloud chamber because it is very easy to build and use, and it has a very good visual aid.
I. The principle function of cloud chamber:
The principle function of the cloud chamber is based on the experience, that steam molecules precipitate on ionised gas ions if it is in an over saturated stream-gas mixture. The alpha particles are known as good ionises on gas molecules, so we can see a small fog-trail on the course of them. With the help of these fog-trails we can make elementary experiments on alpha particles.
II. Necessary components, and sketch:
felt for storing methanol in it
glass cylinder, tube (made of plastic)
a source of alpha-particles
1/2 l thermos bottle, a cold finger
dry ice (an ice made of CO2)
metamid ring (metamid is a type of plastic)
III. Building and using of the equipment:
You should fit the equipment together as it is shown in the sketch. The only problem is the fitting of the glass cylinder with the thermos bottle. I solved this problem with a metamid ring, which should have the follow property:
The metamid ring should be fitted with the thermos bottle, so that the ethanol can't get into the cloud chamber.
Because of the heat-enlargers, there should be a distance of 0,5 mm between the glass cylinder and the thermos bottle.
There should be also a 5-mm hole in the ring, so that we can release the over pressure in the thermos bottle, and that is the same hole, where we bind the direct current to the metal plate at the bottom of the cloud chamber.
At last we paint the ring and the metal-plate black, so that we can reduce the reflection on it.
Put the methanol into the felt, which is fitted to the lid. This evaporated methanol will be our steam molecules. Put to the 3/4 part of the thermos bottle dry ice, and fill it with ethanol, so that you reach the top of the dry ice. Than put the cold finger in it and fit the glass cylinder on the thermos bottle. The source of alpha particles is fixed to the lid. We set the light in the position, where the smallest reflection is, so where you the best see have. If you have iced glass cylinder, you can clean it with a cotton-wool plunged into ethanol. You can see the first fog-trails only 10-15 minutes after the fitting, because it needs time for its terminal equilibrium. After switching the direct current on, that you need to hinder the diffusion of ions outside of the over saturated area. After doing that, you will see 4-5 cm long lines every 0,5-1 second, fluently.
Pictures during the experiments