Wednesday, July 23, 2008

The man who made science modern

kw: book reviews, nonfiction, science, physics, biographies

When someone asked Paul Langevin, whose room at Cavendish Laboratory was next to Rutherford's, if they were friends, he replied, "One can hardly speak of being friendly with a force of nature." The remark supplied the title for a new book by Richard Reeves: A Force of Nature: The Frontier Genius of Ernest Rutherford. The book is not simply a biography; Rutherford has many biographers, most notably David Wilson with Rutherford, Simple Genius. This volume focuses on Rutherford's 1909 discovery of the atomic nucleus and that of particle-induced fission in 1923.

Along the way, Rutherford's life is covered in a brief way, from his boyhood in New Zealand, winning a scholarship to Cambridge in 1895, to professorships in Montreal and Manchester. He was a rare scientist who was an able administrator and promoter of science. Indeed, many of his students became Nobelists, and he introduced, almost unwillingly, the era of large machinery such as particle accelerators. The largest machines of human invention today are particle accelerators that cover several square miles of territory.

It started with a few milligrams of radium, a wisp of gold foil, and a lead block with a slitted hole, all enclosed in a vacuum chamber the size of a hatbox, holding a detection screen and a viewing microscope. Rutherford or an assistant had to sit in the dark for a half hour or so before looking through the microscope to see tiny specks of light produced when an alpha particle, having passed through the foil, or scattered at some angle, struck the screen.

When the foil was a lighter metal, the scattering seemed to be confined to a very narrow band around the image of the slit one would see if the foil were not there. But heavier metals such as gold and platinum produced a wider band and occasional sparkles further away. At one point, realizing these off-center sparkles were telling him something, Rutherford asked for the apparatus to be modified so they could look for scattering at all angles. It was found that a few particles were scattered right back in the direction from which they had come.

Rutherford later remarked that it was "as if you fired a fifteen-inch shell at a piece of tissue paper and it came back and hit you." Alpha particles are heavy and fast. Atoms were then thought to consist of a rather smooth mix of positively- and negatively-charged "somethings" that somehow avoided destroying one another. This experiment indicated that there was something heavy at the center of each atom, containing most of its mass, and that this central mass had a diameter smaller than 10-11cm (now known to be of the order of 10-13cm). In the case of gold, this Nucleus with its 79 positive charges had a long reach and scattered the alpha particles away from quite a distance, in terms of its own size.

Rutherford was a great experimenter (something in which I stand in awe, as I am a rather poor one). He was nearly the last of the "sealing wax and string" workers. Some of the students he inspired became the first room-full-of-big-machines experimenters.

Two of them were John Cockcroft and Ernest Walton. I'd wondered about them since using a Cockcroft-Walton accelerator when I was a physics senior. This image of Walton in his protective cage almost inside the first such accelerator shows what one had to do to avoid being impaled on a bolt of artificial lightning! No matter how you produce it, a large static charge with a potential of half a million volts or so can jump a few feet and fry you just as quickly as your bug zapper destroys a mosquito. At such levels, you don't get electrocuted, you get annihilated! In spite of the risks, Rutherford's "boys" were the first to split a Lithium atom by whacking it with fast protons. Though circular machines soon took over the race to greater energies, a C-W accelerator is a powerful tool even today for certain experiments...and this one is the 1923 model.

Through and behind it all, it was Rutherford's drive and personality that inspired and drove student after student to invent whole new branches of science; he was not just a giant of science but a maker of giants. We need more like him.

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