Cloud Chamber Failure

Question

Me and my friend are trying to build a working cloud chamber to find muons. We’ve built the chamber more than six times, and only the first one worked.

In our latest cloud chamber we used a big plastic box (15x15x20cm), felt to absorb the isopropyl alcohol, and we put the plastic box onto an iron surface that was put on the dry ice. We tried to seal the cloud chamber with hot glue, plasticine, and rubber… It kinda worked for the first 30 seconds and that’s it. Any speculation what’s wrong with our chamber? is it not sealed enough? or maybe something with the amount of the alcohol? we put at least 10ml of isopropyl alcohol on the 15x15cm piece of felt.

Image of the cloud chamber:

Answer 1

I am struggling with making a cloud chamber myself. But the essence of a cloud chamber is a temperature difference. This has to do with the fact that the amount of moisture air can contain is dependent on the temperature. The top should be relatively warm so that the air can contain a lot of evaporated alcohol. And the bottom should be relatively cold so that it cannot hold much alcohol and thus condensates.

The problem in your cloud chamber could be that just the bottom is really cold but the top is not warm enough. This way the whole chamber just gets really cold and then there is no temperature difference. This could also be an explanation of why it only works in the first few seconds. Becasue at first the temperature of the top of the/whole chamber is room temperatuur. But then it quickly cools down. I assume that the big bowl on top is where you put warm water in? It might be that the plastic is not conducting the warmth enough to the filt. Plastic is not a good warmth conductor. You first have the plastic bottom of the bowl and then the plastic of the top of the chamber. That are two layers of plastic the warmth need to go through.

As a possibe fix I would try to put a metal bowl of hot water on top (for example a big frypan). Besides that, the filt really needs to be soaked with alcohol. (First get rid of the surplus alcohol before you put it on the dry ice). I also recommend using a really pure isopropanol (I have 99.9%). I would also recommend using a black (metal for conductivity) bottom plate, because it makes the trails more visible.

Answer 2

I'm a little bit late in my answer. I'm building a cloud chamber myself. There are several details you have to pay attention to. First there is the temperature gradient between the upper part and the lower part of the chamber. You are using dry ice, which can make the bottom temperature very low, this could prevent the upper part of the chamber from reaching a sufficently high temperature, therefore the alcohol doesn't evaporate: a temperature of about 30 to 40°C could do. To do this you could use heating elements or resistors connected in series inside the sponge you are putting your alcohol in, using the joule effect.

Moreover a thing that worked for me is to include a high voltage source. You could use the circuit of an electrical fly swatter, which - in my case - could generate 3-4 kV (1-2kV should work just fine). In most of these circuits you can find a button that activates the high voltage generator: to make the potential difference constant you could short the button terminals. The output of the high voltage circuit have to be connected to a metal mesh/grid on the upper part of your cloud chamber and to the plate (if it is a copper or aluminium plate) on the lower part. This generates a relatively strong electric field which makes a huge difference. In my experience it changed from seeing nothing to seeing the characteristic particles traces of the background radiation.

Hope that helped!