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Wednesday 23 May 2001
The Halo at the Centre of the Atom

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Professor Ian J Thompson,
MSc (Massey), PhD (Auckland) C.Phys, F.Inst. P

Professor of Physics
School of Physics and Chemistry

At the centre of every atom is a tiny dense nucleus that makes up most of its mass, and determines what kind of element it is. All the elements that are necessary for life on earth have been formed in stars long ago, and spread out by supernovae explosions to form the ingredients of the earth and other planets.

In order to understand how all these elements are produced, we have in Nuclear Physics to understand not just the elements we find on earth now, but also those varieties of elements that appeared fleetingly in stellar explosions. In the last 20 years, physicists have been able to recreate many of these short-lived varieties, and have discovered many new features not seen in their long-lived cousins.

Most stable nuclei have approximately equal number of protons and neutrons (the protons have a positive charge, while the neutrons form a neutral glue holding the nucleus together). Now, however, we discover that there was once, and are now again in the laboratory, some exotic nuclear varieties with many more neutrons than protons. Sometimes these extra neutrons form a large halo around the protons, in the nucleus at the centre of the atom. We have discovered that the halo is much larger in size than the range of the force which contains it.

I will look especially at some this and other strange properties of nuclear haloes: how we need to use the wave features of modern quantum physics to see how they can even exist at all, how we measure their properties, and what possible use such atoms may have again. 

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