From The Royal Institution.

Some atoms are radioactive, waiting to explode. Eric Rogers discusses how we study this and its uses in his fourth Christmas Lecture.

Watch all the lectures in this series here: https://youtube.com/playlist?list=PLbnrZHfNEDZzOq1zfje2o8Y_nIrHmdtbX&si=Q6s4EbX1BAGz-KlO
Watch our newest Christmas lectures here: https://www.youtube.com/playlist?list=PLbnrZHfNEDZyQJZLPMjwEoOLdkFBLU2m1

This was recorded on 4 Dec 1979.

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This year marks 200 years of the Royal Institution Christmas Lectures — a world famous series showcasing science, curiosity, and mind-blowing demos, and started by the legendary Michael Faraday himself.

To celebrate, we’re unlocking the archive. Every Saturday, we’ll upload a classic lecture to our YouTube channel — some not seen since they aired on TV. Sign up as a Science Supporter and get early access here:
https://www.youtube.com/channel/UCYeF244yNGuFefuFKqxIAXw/join

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From the 1979 programme notes:
Most atoms are stable, carbon, hydrogen, oxygen, gold and many others. They stay the same from now to doomsday – except for swapping loose electrons in chemical compounds or in making ions.

But some atoms are radioactive, waiting to explode and hurl out a small ‘chip’ thus becoming quite a different atom – an atom of a different chemical element. The ‘chip’ flies out with so much energy that it knocks electrons off hundreds of atoms in the surrounding air — using electrical forces as it flies past. That was how radioactivity was discovered, by the ionization it causes.

And that is how it can sometimes hurt, or cure, your body, by making ions. See a radioactive sample making ions that are driven by an electric field, in a tiny measurable current. Watch three ‘mystery experiments’ which prepare for radioactive measurements. See Geiger counters respond to three kinds of ‘chips’ from different radioactive materials – alpha particles (heavy but speedy), beta particles (just high-speed electrons), gamma rays (fastest of all, very short X-rays).

Watch a stream of beta particles pulled into orbit by a magnetic field. The ions formed in wet air by flying ‘chips’ attract water molecules electrically and thus form starters for water drops in a cloud. A cloud chamber makes use of that and lets us see the track of a ‘chip’ as a thin line of tiny water drops. See a cloud chamber in action, then look at photographs of special events in it. Those show the clearest evidence for nuclear atoms. The tiny explosions of radioactive atoms seem to happen by pure chance, at random.

But if we have a vast quantity of them the tale of random events smooths out to a steady rate. If we start with a large stockpile, a Geiger counter will show many explosions each minute, then fewer as time goes on — fewer because the stockpile has grown smaller. After a certain time the stockpile has dwindled down to half what we started with, and we call that time the half-life of that radioactive material.

That law of decay, with a constant half-life, is characteristic of all radioactive materials; and it is essential for people to understand it before they discuss dangers and values of nuclear power. So we shall offer illustrations and show a real example of radioactive decay.
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About the 1979 CHRISTMAS LECTURES
Except for clever suggestions, our knowledge of atoms is very young compared with our older scientific knowledge. Some of it is a few centuries old but much of it is only one century old at most. There are two reasons for that late development. First: since atoms are (as we now know) far too small to be seen, all our experimental gathering of knowledge has to be indirect. Although we now know a great deal about atoms, and about the still smaller parts of atoms, we still have to describe them by imaginative pictures which we call models.

Second: even to build such knowledge indirectly, new apparatus had to be developed, such as vacuum pumps and electronic supplies for high voltage. The aid of a vast new technology was needed.

Nowadays when one learns what has been discovered about atoms one has to learn by hearsay, one has to accept the indirect methods and swallow the picturing by imaginative models. Then a keen listener must long for some experimental support or illustrations. That is what these lectures will offer in their ‘circus of experiments’. The circus cannot cover all our new knowledge of atoms but it will, we trust, give visitors a feeling of friendly first-hand acquaintance, a contribution of confidence and understanding as well as a delight in seeing experiments.

Find out more about the CHRISTMAS LECTURES here: https://www.rigb.org/christmas-lectures