The Fly in the Cathedral: How a Group of Cambridge Scientists Won the International Race to Split the Atom

Natural History, June, 2005 by Laurence A. Marschall

The Fly in the Cathedral: How a Group of Cambridge Scientists Won the International Race to Split the Atom by Brian Cathcart Farrar, Straus and Giroux, 2005; $25.00

For a man who admits he never took a class in physics, Brian Cathcart certainly knows how to turn great science into arresting drama. The scene is the Cavendish Laboratory in Cambridge, England, in the late 1920s. Scientists, just beginning to unlock the secrets of the atom, had been astonished almost two decades earlier by the discovery that matter is mostly empty space; orbiting the nucleus of each atom, like a system of miniature moons, is a cloud of electrons, particles with negative electric charge.

The seminal figure who had first proposed the existence of a dense atomic nucleus was Ernest Rutherford, an inventive, New Zealand-born physicist. In 1909, while at the University of Manchester, he devised a plan to bombard gold atoms with alpha particles, or positively charged bits of matter emitted by the radioactive element radium, and then watch what happened to the alpha particles after they penetrated the material: How often did they hit something solid, and how often did they pass straight through? Day after day, a student in Rutherford's laboratory stared through his eyepiece, tallying the faint flashes of fight that signaled the arrival of an alpha particle recoiling off something very dense in the gold atoms--the nuclei.

By the late 1920s, most of the mass of the atom was known to reside in the positively charged nucleus at its center, a kernel a hundred thousand times smaller than the atom itself. It had been tough going to probe this far into the atom, yet the success of the efforts, it seemed, only deepened the mystery: Was the nucleus a single particle or, like a nested Russian doll, was it only the threshold of further nanoworlds within?

Rutherford knew that alpha particles, which readily pierced the atom's cloud of electrons, didn't have enough energy to penetrate and pry apart the nucleus. Since the probe particles bore a positive charge, just like the nucleus, the probe and the nucleus repelled each other. What was needed, Rutherford realized, was a way of accelerating the particles to ultrahigh speeds, so that they would slam through the electric barrier that walled off the nucleus from like-charged intruders.

Rutherford assigned the task to two young Cavendish Laboratory physicists, Ernest T.S. Walton and John D. Cockcroft--the heroes of Cathcart's story. Although atoms are minuscule, Rutherford's proteges knew that any device that could shoot particles into an atomic nucleus had to be physically huge: the charged particles would have to be propelled by special guns powered not by black powder but by millions of volts of electricity. As their research progressed, Cockcroft and Walton's laboratory began to fill up with industrial-strength transformers and pumps that might have looked more at home in a Manchester mill than on the venerable Cambridge campus.

Cathcart's drama is leavened by colorful characters popping in and out of the narrative, most notably the Russian-born American physicist George Gamow. A practical jokester and raconteur, Gamow not only played Falstaff to the Cavendish crew, but he also made the crucial calculations of the voltage needed to crack the nucleus. And the team's race for scientific glory had all the usual obstacles: equipment breakdowns, blind alleys, competition from other groups of physicists. The struggle reached its climax in April 1932, when, after several years of repeated experiments, high-voltage protons from Cockcroft and Walton's accelerator penetrated the nuclei of lithium atoms, splitting the nuclei in two. "The Atom Split," the newspapers proclaimed--and the rest is history.

Cockcroft and Walton won the 1951 Nobel Prize in physics, a recognition not only of a great leap in understanding nature, but also of a fundamental change in the research enterprise. Gone are the days when you could investigate the atom on a tabletop. The mysteries of the atomic nucleus are now being explored by accelerators that encircle areas as large as Swiss cantons, with annual worldwide budgets of many billions of dollars. In nature, it turns out, the smaller the subject, the harder and costlier it is to study.

LAURENCE A. MARSCHALL, author of The Supernova Story, is W.K.T. Sahm Professor of Physics at Gettysburg, College in Pennsylvania. He is the 2005 winner of the Education prize of the American Astronomical Society.