Seeing cosmic rays

By Aimee Whitcroft 15/06/2011 4

Like, for real. With the naked eye.

Cosmic ray tracks in a cloud chamber
Cosmic ray tracks in a cloud chamber

Another post courtesy of Josh Bailey*, who has been building cloud chambers and documenting the resulting, well, results. I _meant_ to write on the subject, since it’s so frikkin’ cool, but have been somewhat swamped by other things in which I am involved**.

So! Without further ado:


I always find devices that let you observe some basic, not to mention beautiful property of the universe irresistible. And cloud chambers are the very definition of such devices.

A cloud chamber uses cool alcohol vapour to make visible – in real time, right before your eyes – the trails of the particles (from alpha particles to high energy cosmic rays) that would otherwise invisibly pass you by – or even make their way through you. Particles move through the vapour leaving an ionised (slightly charged) trail – that causes the vapour to condense in a visible streak.

The key operating feature is the cool alcohol vapour that makes the trails visible. There are different cloud chamber designs (that differ in how the vapour is generated, how the trails are illuminated and cleared). The most simple chambers use dry ice to provide the vapour – but the system I’m going to describe here uses a cold water, a heat exchanger and a Peltier cooler.

It is almost as simple as just add water. Cold water is pumped through a heat exchanger, and a Peltier cooler is sandwiched in between the exchanger and a round chamber containing a little isopropyl alcohol, all at ordinary air pressure. The cooler continuously extracts heat from the chamber, causing the alcohol to turn into a vapour. LEDs are situated at the base of the chamber, illuminating the coldest vapour that is just on the point on condensation – ripe for some hapless particle to ionise.

The last remaining feature to describe is a high voltage (modestly high voltage – 1000s of Volts, at a very low current) to sweep away old ions. This is introduced by a metal pin at the top of the chamber, connected to the a high voltage supply.

Pictures here

Video here



* Who appears to be enjoying writing about his…projects :)

** More details on those soon. Just think nerdnite Wellington. And an art exhibition. And, um, a host of other things bubbling away, too :)

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