The Modern Alchemist: Cloud Chamber

Behind the Scenes of the 2012 Christmas Lectures

2 footnotes:

The birth of Helium atoms.

On the last day of recording the 2012 Christmas Lectures Dr Peter Wothers illustrates the properties of Air with a beautiful demo from his final Lecture.

The Cloud Chamber shows the natural radiation in the atmosphere. When the charged alpha particles and smaller beta particles fire through the alcohol-heavy atmosphere in the chamber they cause little droplets to form leaving cloud-like trails.

When Dr Wothers introduces a sample of the artificially-produced radioactive metal Americium into the chamber the alpha particles emitted (with their two protons and two neutrons) grab electrons and form Helium atoms.




Dr Peter Wothers
Royal Institution, London
Filmed in:
The Theatre

The Roayl Institution

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cc_by-nc-sa License: Creative Commons




So here we are on the last day of the recording for the Christmas Lectures, but I thought I'd take an opportunity to point this out because it's so beautiful. This is a really stunning cloud chamber, and the tracks that you can see here show just the natural radiation in the atmosphere around us.

So if we actually have a look in here, you can see sometimes there are thicker tracks which are big heavy alpha particles. Sometimes they're little wispy ones, which are beta particles. But all of these, they're all working in the same way. So the atmosphere in here contains a lot vapour of alcohol. And it's sort of more than it should have. And when these charged particles fire through the atmosphere in here, they cause little droplets to form, and those are the clouds that you're seeing.

So this is a similar sort of thing to when you get a track behind an airplane. There's a lot of moisture in the atmosphere and it's just the exhaust, just helping those drops of moisture to form together and leave that cloud.

And this is a tiny little sample of the element called Americium. And this is used in smoke detectors. So you've probably got some of this in your home, at least you should have.

So this is an artificially produced metal. And as soon as this is introduced, look at that. What we're seeing here are tracks from the alpha particles emitted from this radioactive source. And these alpha particles, with their two protons, two neutrons, and they grab electrons and form Helium atoms. So what you're seeing here are the birth of Helium atoms.


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