About Me

My photo
I live in Bedford, England. Having retired from teaching; I am now a research student at the University of Bedfordshire researching into Threshold Concepts in the context of A-level Physics. I love reading! I enjoy in particular fiction (mostly great and classic fiction although I also enjoy whodunnits), biography, history and smart thinking. I have also recently become a keen playgoer to London Fringe Theatre. I enjoy mostly classics and I read the playscripts and add those to the blog. I am a member of Bedford Writers' Circle. See their website here: http://bedford-writers.co.uk/ Follow me on twitter: @daja57

Thursday, 14 July 2016

The Fly in the Cathedral" by Brian Cathcart

From its very beginning, relating the 1909 discovery of Rutherford alpha particle scattering in which a final year undergraduate named Ernest Marsden saw something that contradicted all previous theories of the atom, Cathcart manages to capture both the tedium of live research science (Marsden has to follow a procedure including sitting in a darkened room for 20 minutes before taking observations; when he sees the 'wrong' thing he spends a week checking and rechecking every part of his apparatus before becoming certain of his results) and the excitement of discovery.

From there, Cathcart explains how Ernest Walton arrived at the old Cavendish laboratory in Cambridge where the world famous Rutherford resided (I had lectures there when an undergraduate in a lecture theatre which James Clerk Maxwell designed but most of the building at the time had been sealed off because it had been contaminated by the experiments of Rutherford and his team). This was 1927 when the laboratory was not as fertile as the glory days before the first world war and there was a certain pressure on all involved to make more ground-breaking discoveries. But to attack the nucleus would need particles moving extraordinarily fast so that they could overcome the electrostatic repulsion of the nucleus, so Walton, working with John Cockcroft, started to build a particle accelerator. Given that the National Grid was in its infancy, using transformers to up ac to the hundreds of thousands of volts they believed they needed and then building rectifiers and vacuum tubes capable of standing these high voltages without either bursting or electrocuting the experimenters (Walton had to crawl across a wooden floor to approach the wworkign apparatus) was a formidable technical challenge made possible mostly by Cockcroft who, having served with distinction in the war,  had previously worked with Metropolitan Vickers the electrical engineering company in Manchester (where my wife's gradnfather worked).

A number of other experimenters in the US were working on the same ideas, notably Tuve using a static generator designed by his friend Van der Graaf, and Tuve's childhood friend Ernest Lawrence who was building a cyclotron. Nuclear disintegration was also being studied by Joliot and Curie (the daughter) in Madame Curie's lab in Paris, and by Otto Hahn and Lise Meitner in Berlin.

And the quantum theorists were kicking off. The 1920s were the glory days of Rutherford's old buddy Nils Bohr in Copenhagen, and Werner Heisenberg and Max Schrodinger in Germany. Louis de Broglie's 1924 theory of wave particle duality was being discussed and an amazingly enterprising Russian named Gamow turned up one day at Bohr's lab in Copenhagen. Bohr was busy and Gamow was given an appointment in a few days time but after he explained he only had money to survive a single day the secretary took pity on him and he saw Bohr that afternoon who immediately arranged for him to stay. Gamow then worked out that wave function particles could penetrate the nucleus at much lower energies.

But Walton and Cockcroft toiled at their apparatus, evacuating tubes that leaked and sealing the leaks with Bank of England sealing wax (they later found that plasticine did a better job) for several years.

At this stage everyone knew that the atoms was composed of electrons orbiting (in set orbits) a very tiny nucleus which had protons in it. But the nucleus must also have either neutrons (Rutherford's theory) or electrons. The electrons were the favoured theory because beta radiation involves electrons leaving the nucleus; neutrons were purely speculative and scarcely mentioned in polite circles. So when Curie and Joliot discovered radiation flowing from a beryllium target that had been bombarded with radiation from polonium, everyone assumed that the neutral rays must be gamma rays even though they packed much more of a punch than seemed possible for gamma rays. But Chadwick, Rutherford's deputy at the Cavendish, revived the neutron theory and showed that they radiation was a stream of neutrons. This was in February 1932. Almost immediately a grumpy Rutherford told Cockcroft and Walton that they had better stop tinkering with their apparatus in an attempt to improve it and use it to fire protons at something. They set up a lithium target, fired the protons in and immediately discovered, still using the scintillation technique that Marsden had used, alpha particles.

Over the next few weeks they frantically repeated their results and worked out the implications whilst sworn to secrecy (Walton told his girlfriend, Cockcroft his wife, Rutherford told Bohr). The disintegration was caused because the protons were absorbed into the lithium nucleus which then spolit into two alpha particles. This was happening at a far lower energy than they had expected, partly because protons do the 'quantum tunnelling' described by Gamow at significantly lower energies than alpha particles but also because the quantum tunnelling is a probabilistic effect and they were generating millions more protons than had been available with the old techniques of relying on radium sources to emit alpha particles. Another 'problem' was that the alpha particles had higher energies that the energies of the incoming protons but this was resolved when it was realised that two alpha particles have a lower mass than a lithium nucleus and a proton and than this mass loss was being converted into energy through Einstein's most famous equation: E=mc2. They had split the nucleus.

This is a wonderful tale of impoverished graduate students in a worldwide fraternity working with string and sealing wax to do cutting edge research. Cathcart writes brilliantly, the tale fairly bowls along, and gives full play to the human stories behind the geeks.  The excitement of the times is vividly captured as is the hard work necessary and the oddness of the characters.

This is a fabulous book. It appears to be out of print. Why??????

July 2016; 274 pages

Another brilliant book about this time is The Strangest Man by Graham Farmelo which tells the story of quantum theorist Paul Dirac.

No comments:

Post a Comment