Hi all
I am sooo frustrated with our cloud chamber. it is fairly old but the light works and the source can be detected on our IEC geiger counter so all should be good.
Well, we have never had it work and we tried again today and it still doesn't work!!!
The students made their own chambers using the ANSTO cloud chamber experiment and using our school sources and we still get anything.
HELP!!! it drives me made when I cant get things to work that seem simple.
cloud chamber
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bigmack
- Posts: 816
- Joined: 15 Dec 2015, 10:49
- Job Title: Lab Technician
- School: FCAC
- State/Location: QLD
Re: cloud chamber
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
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
Re: cloud chamber
Thank you for such a great explanation
-
bigmack
- Posts: 816
- Joined: 15 Dec 2015, 10:49
- Job Title: Lab Technician
- School: FCAC
- State/Location: QLD
Re: cloud chamber
Thanks Sunray18
At my other school I found two of these Silform Diffusion Cloud Chambers in almost usable condition ....but they looked like they haven't been used in years . The radiation sources were nowhere to be seen .
One box still had the original 90V battery in it but it was dead flat and some very faded instructions ...I scanned them but its hard to read in places .
Anyway...I hope this may help others with the same equipment to identify what they have .I would suggest giving it a go if you have all the bits needed. The battery issue may be a problem unless you have a Bench power supply that can do around 90-400 volts .
The other issue is getting hold of Dry Ice or Liquid nitrogen
I would be concerned a bout the Risk of it toppling over and the liquid Nitrogen spilling . So I would find a way to hold it securely
At my other school I found two of these Silform Diffusion Cloud Chambers in almost usable condition ....but they looked like they haven't been used in years . The radiation sources were nowhere to be seen .
One box still had the original 90V battery in it but it was dead flat and some very faded instructions ...I scanned them but its hard to read in places .
Anyway...I hope this may help others with the same equipment to identify what they have .I would suggest giving it a go if you have all the bits needed. The battery issue may be a problem unless you have a Bench power supply that can do around 90-400 volts .
The other issue is getting hold of Dry Ice or Liquid nitrogen
I would be concerned a bout the Risk of it toppling over and the liquid Nitrogen spilling . So I would find a way to hold it securely
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