Hi glenpaul . Just wondering what type you have .
Here's a few things about them I have discovered while trying to get one to work for us .....If, I'm telling you how to suck eggs , sorry ....otherwise I hope it is useful to you or others. I am no expert but this is from my playing with them .
The basic principle is that a chamber has a saturated layer of alcohol .When a particle released from a radio active source moves through this layer it causes the alcohol to condense and a vapour trail is left .The condensed alcohol trail slowly falls to the bottom .
There are two main techniques used to make this saturated alcohol layer .
The first is to use a cold substance such as liquid nitrogen or dry ice to cool the bottom of the chamber to about -30 degC or lower , this causes the alcohol which is evaporating from the felt ring to saturate as vapour but as it is cold it forms a dense layer .
Some school cloud chambers had a thermos flask that was filled with liquid nitrogen while others had an area underneath where you can pack in dry ice . often these have a sponge or spring to keep the block of Dry ice in contact with the bottom of the chamber .
The second method is to use a hand held vacuum pump or large syringe and
Quickly suck the air out of the chamber . The
Sudden drop in pressure causes the alcohol to saturate .
Which ever method is used , there must also be a
Clearing voltage . This is to "mop" up ions in the chamber.
If you do not have a clearing voltage , you will not get any action .There are two usual methods .
One is to use a perspex lid on the chamber and periodically wipe it with a soft cotton cloth .( almost rubbing it in a circular motion like you are polishing it ) It will generate a static charge ........you need to do this say every two or three minuates ......incidentally this works really well .
The other method is to have a "halo" electrode at the top of the chamber and an external power supply usually between 90 and 400 Vdc is applied between this and a plate in the bottom of the chamber . ( this is why some old Cloud chambers used 90 v batteries ......these batteries were commonly available then as they were used in portable valve radios )
For alcohol I have found no difference using Methalated spirits , Iso propal or ethanol.
apply enough to the felt ring to just load it ....you don't want it pooling everywhere .
The Cooled type of cloud chamber are the best type in a classroom as they work continually whereas the vacuum type only work for around a second or two after you pull the plunger ...they can be quite frustrating and as I said you must quickly operate the plunger as slowly operating it you will get no action .
The best sources are Alpha as they have strong defined lines . So When I'm setting it up I use an Alpha source , then when the chamber is operating , switch to the beta as they are harder to see , Our gamma source has never worked particularly well.
And another thing is set it up ,
put the lid on it and don't keep opening it . Every-time you open it , it takes a minute to settle down again .( it takes time in a cooled chamber for the tempurature equalibrium to re-establish ) .
We have frustrated teachers that keep fiddling with it and could never get it to work . So now they get me to set it up in the class and , they talk I do
Incidentally it's becoming popular to use cloud chambers that cool with Peltier devises and heat ex changers like are used in PC processor . Plug'm in and away they go ...( still got to add alcohol ) ...but they are very expensive commercially available .
After not being able to buy dry ice , I consulted google and figured I could convert ours to run on Ice water and electricity .....but I love doing things at home