In 1900, the predominant model of the atom was a plum pudding.
Electrons, discovered in 1897, were thought to be like plums speckled through a mysteriously electrified, spherical atomic sponge. Then in 1909, a student of Ernest Rutherford bombarded a gold target with particles and a few of them rebounded, causing scintillations on the glass screen of his microscope. The atomic nucleus had been discovered: it was as if, said Rutherford, "you fired a 15in shell at a piece of tissue paper and it came back and hit you". The plum pudding model went out the window.
But how to penetrate the nucleus? What made it so massive? What forces held it together? In other words, how might scientists catch and dissect "the fly in the cathedral", as the nucleus became known.
Brian Cathcart's book is the story of the period between 1909 and 1932, when the nucleus was split by John Cockcroft and Ernest Walton working in Rutherford's Cavendish Laboratory at Cambridge; and Einstein's famous equation relating energy and mass received conclusive experimental confirmation.
The Fly in the Cathedral is a happy blend of theoretical and experimental physics and technology with the personalities of the ten or so major contributors to the "splitting of the atom". Although Cathcart is a former journalist who admits never having had a physics lesson, he is plainly in love with his subject, and his affection shines throughout, especially in his ability to dramatise the trials and tribulations of experimental physicists. Without his ever using the silly, giveaway word "boffin", one comes to feel how "apparatus tended to be personal... not just a tool but also something to be nursed and cajoled over months and even years, and to be admired and shown off when it did its job". Perhaps it helps to share his fascination, and, like this reviewer, to have lived with such work; but I would guess the book will also appeal to those interested more in the ground-breaking results than in the tortuous process of getting there.
The incidental details are often surprising and thought-provoking. In Walton's first lodgings in Cambridge, in 19, the only electric fitting was a light, for which he had to pay extra. A telephone exchange was not installed in the Cavendish, the UK's leading academic laboratory, until 1932, only a few weeks before the breakthrough experiment. As an iron rule, work had to stop at 6pm sharp, when the technicians pulled the plugs and threw the switches; Cockcroft and Walton needed special dispensation from Rutherford to work late.
Perhaps the most significant revelation is of the chanciness of scientific research. Cockcroft, Walton and Rutherford were astonished that the nucleus could be split using potential differences of a mere 125,000 volts. In the late 1920s, physicists were convinced it would require energies nearer to a million electron-volts, and robust power supplies to generate them. This meant that the Cavendish team's later, more powerful apparatus was unnecessary. Furthermore, if Cockcroft and Walton had thought to put a scintillation screen beside their lithium target in 1930, they would have detected splitting with their original apparatus.
Again, Chadwick's simultaneous discovery of the neutron, inspired by a French paper written by the Curies, was possible only because he happened to have obtained some polonium from the US and a particle counter of sufficient sophistication from a colleague.
Occasionally, Cathcart betrays his non-scientific background. The explanation of quantum theory in terms of "continuous" milk (waves) and "discontinuous" eggs (quanta) is strained; and voltage does not "pass" between electrodes. But overall, his book is a remarkable achievement, eminently readable for non-scientists.
Andrew Robinson is literary editor, The Times Higher .
The Fly in the Cathedral: How a Small Group of Cambridge Scientists Won the Race to Split the Atom
Author - Brian Cathcart
Publisher - Viking
Pages - 308
Price - £14.99
ISBN - 0 670 88321 2
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