By Hamish Johnston

Olivia Donovan of Halifax, Nova Scotia sent us a link to this video she made about how to make a diffusion cloud chamber from simple household items.

My favourite bit is when Olivia (age 15) demonstrates how to remove a radioactive piece of americium from a smoke detector. “Try not to point it directly at you,” she advises.

The americium provides the charged particles, which are detected in the chamber when they cause droplets to condense out of a super-saturated vapour of isopropyl alcohol. The chamber is cooled using an “air duster” – a can of compressed difluoroethane – and in the video Donovan shows how a few blasts of difluoroethane can cool a thermocouple to –45 °C.

It’s a lovely little experiment, and amazing to think that it can be done at home.