UCL – Physics Department

I discussed ionising radiation and cloud chambers with Dr. Gareth Hesketh, an experimental particle physicist at UCL. He discussed with me exactly what is happening when radiation ionises in a cloud chamber. A cloud chamber basically makes the invisible visible – allowing us to see ephemeral puffs of tiny particles that started in outer space and shoot through all of us all the time.

I am interested in the spontaneity of the appearance of the clouds, and their omnipresence. Their existence almost holds a godlike position for me.

I wanted to get my Philip Harris cloud chamber to work – it needs an E.H.T. power supply. Once it is running, I want to use a blue light (not an ordinary light). This is important, Gareth explained, as it makes the particles more visible. He discovered this through experimentation. This blueness reminded me of the aerogel I had looked at earlier on in the day – this extremely light and material made predominantly of oxygen – and the blueness is caused by the same phenomenon that gives colour to our Earth’s atmosphere, namely Raleigh scattering of light. I would like to see if there could be some way of combining the aerogel with this project – its light transparency would match well with the wispiness of the radiation. It is possible, also, that the materials would ‘converge’ for some sort of serendipitous event.


I had been concerned with the safety implications of working with ionising radiation since I started the project. Dr. Hesketh helped to assuage my doubt about using the apparatus – the alpha particles that would be given off don’t go very far, and may not even escape the chamber itself. A piece of paper can be enough to stop them. I recall Cornelia Hesse-Honegger’s paintings depicting mutations she observed in insects living around Chernobyl.


A good way of displaying the tracks, Gareth suggested, was to use a projector next to a tank.

I am going back next Wednesday to have my chamber checked with a Geiger counter and to see some working cloud chambers.