The DIY Cloud Chamber
The cloud chamber is a simple particle detector that uses a
super-saturated alcohol layer to pick up tracks of ionising
radiation. More background can be found at royalholloway.ac.uk/PPresources.
Materials:
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perspex tank – cheap fish tanks are often suitable – dimensions of 15 x 15 x 30 cm or
similar
rags/felt/cloth that can be soaked in alcohol
alcohol (isopropanol is suitable)
black metal sheet to fit the bottom of the tank
insulated box to place tank in
dry ice
strong light source – e.g. old projector
Method:
1. Attach the cloth that will act as the alcohol reservoir around the inside of the tank.
Beware, the alcohol may degrade some glues. Silicone sealant could be used for
this.
2. The metal sheet must fit tightly around the top of the chamber (in place of the lid if
using a fish tank, for example). Colouring it black, or covering it in black tape is
essential for increasing the visibility of any particle tracks.
3. Construct an insulated box (any foam insulation or similar should be suitable) for the
dry ice to sit in.
4. To run the chamber, first soak the cloth in the chosen alcohol.
5. Drip some more alcohol on to the side of the metal sheet that will be inside the
chamber and then place it on the chamber. Seal the edges thoroughly using duct
tape or similar, this is important to prevent air flow at the edges interfering with the
saturated alcohol layer.
6. Upend the chamber so the alcohol reservoir is at the top and place it on a layer of
dry ice in the insulated box.
7. It will take ~10-15 minutes for an appropriate temperature gradient to form and
tracks to appear.
8. Have a play! Given the wide range of designs and materials possible it is likely that
you may need to iterate your design a few times before you see particle tracks. Key
points are:
 A large temperature gradient between reservoir and metal sheet. Placing the
reservoir too high can adversely affect this.
 Suitable lighting – a strong light source is needed and it may be necessary to
block other light to ensure good visibility.
 Stable atmosphere in the chamber – as there is a temperature gradient, air
will want to move around. Any leaks can disrupt the super-saturated alcohol
layer.
 Viewing angle – particle tracks are often not visible from all angles (top down
for example). Move around and find the best place to see them.
Safety:
Follow the normal safety procedures for using both solvents and dry ice. Take care when
cutting up insulating material as some of these can be dangerous if not using a ventilator.
For any questions, further advice, or more demos, visit
royalholloway.ac.uk/physics/outreach or email physics.outreach@rhul.ac.uk.