Build Your Own

• Connect the Peltier modules and fan to a power supply 

  • For the two modules used, Steve found that a 8V/ 6A/ 50W supply was sufficient.

  • Having a variable-voltage bench power supply has the advantage of being able to vary the power to see the effect on the base temperature reached by the cold plate. However, a fixed-voltage power supply should be fine, providing it can supply the necessary current.

  • Many amateur astronomers use a 'power tank' to power telescope mounts, cameras, dew heaters, etc, and these should provide plenty of power for the Peltier modules. 

  • If you haven't already got one, fixed-voltage power supplies are reasonably priced – for instance, a 9V/ 6A power supply can be bought for ~£10 – £15. 

• Place a sponge on the inside of the top of the jar 

  • The size of the sponge is not important, but it should be enough to soak up a few ml (cc) of IPA. A circular cosmetic sponge with a diameter less than that of the jar and ~1cm thick is ideal.

  • If using a pickle jar, glue the sponge inside the base of the jar so that it is at the top when the jar is inverted. If using an open-ended glass cylinder then the sponge can be glued to the underside of a felt coaster and the coaster placed onto the top of the cylinder. 

• Pour/spray about 5ml (5cc) of IPA onto the sponge 

  • The sponge should soak up the IPA. If it doesn't then either the sponge is too small or you have gone overboard with the IPA. 

• Place the jar onto the cold plate of the Peltier module 

  • The air in the jar needs to be in good thermal contact with the cold plate to ensure that the IPA vapour gets cooled enough to condense into a liquid. If using a jar with a lid, some thermal paste between the lid and the cold plate will improve the transfer of heat, especially if the lid is not absolutely flat.

  • Placing the jar onto the cold plate without the lid in place makes the heat transfer more efficient. Using an open-ended glass cylinder gives the same results as using a jar without its lid. 

• Place the USB mug-warming coaster onto the top of the jar 

  • This will provide heat to the top of the jar and hence the IPA-soaked sponge inside. Only a modest level of warming to about 30 – 40 °C is required, but some USB coasters get quite hot (above 50 °C). Hence you can either: (i) keep the coaster the right way up so that the heat getting through to the bottom of the coaster warms the jar; or (ii) invert the coaster but use something to separate the hot surface of the coaster from the jar. I used a felt coaster 5mm thick to do this.

  • If your budget doesn't stretch to a USB mug-warming coaster (~ £10) then you can try carefully placing a cup of tea onto the top of the jar. It will probably provide all the heat required, but may need replacing with a fresh cup every once in a while. I call this the "Cuppa Cloud Chamber" option. Try it at your own risk. 

• Plug the Peltier cooling module(s) into a suitable power supply

• Plug the mug-warming coaster into a USB port

  • The time taken for the cloud chamber to reach the optimal conditions for observing particle tracks will depend on the amount of IPA inside the jar and the temperatures at the top and bottom of the jar. As a rough guide, I found that... 

    • Peltier modules will cool from room temperature to –20°C in 5 minutes. 

    • The IPA-soaked sponge will warm from room temperature to 30°C in 10 minutes. 

• Shine some light into the side of the jar 

  • A simple LED torch should be enough. Illuminate the inside of the jar from the side as viewed by the observer(s) or camera. When the IPA starts condensing a mist will appear to form at the bottom of the jar as tiny droplets of IPA drizzle down onto the cold plate. This should be visible after about 5 minutes 

• Wait for cosmic rays 

  • If you can't see any particle tracks then you can never be quite sure whether the right conditions have not yet been reached or whether there are not many cosmic rays or other particles from background radiation passing through your cloud chamber. One way around this dilemma is to place a radioactive source close to, or inside, the cloud chamber. That's not as dramatic as it sounds, as radioactive sources can be acquired without putting you on any government watchlists... 

    • Many naturally occurring minerals contain uranium, thorium or potassium and contribute to background radiation throughout the world. 

    • Some glass objects may have had a few % of uranium compounds added to give them a characteristic greenish colouration. 

    • Tungsten welding rods may have had a few % of thorium added to improve the quality of the welds. 

  • The radiation from any of these sources in close proximity will be more intense than the radiation from cosmic rays and so can be used to confirm whether or not the cloud chamber is working. 

If you want to learn more about Steve's outreach and a demonstration of his cloud chamber, there is a great video you can find below where Steve is giving an outreach talk to the Southport U3A (SoU3A) Astronomy Group on 22 May 2024.