Probing the Nucleus
The Fly in the Cathedral: How a Group of Cambridge Scientists
Won the International Race to Split the Atom. Brian
Cathcart. xii + 308 pp. Farrar, Straus and Giroux, 2004. $25.
Popular histories of 20th-century physics tend to present the
revolution of quantum mechanics as having been more or less
completed by the late 1920s. This portrayal obscures the problems
that still plagued several areas of physics at the time, including
what would come to be known as nuclear physics. The Fly in the
Cathedral, by reporter-turned-science-writer Brian Cathcart,
highlights these difficulties, some of which were solved by
experiment in 1932, a celebrated year in physics.
Cathcart begins with the 1909 experiment that led Ernest Rutherford
to the nuclear model of the atom, in which almost all of the atom's
mass is concentrated in the middle; the nucleus is the tiny
"fly" in the cavernous "cathedral" of the atom.
Cathcart then jumps ahead to the problems besetting the nuclear
model in the late 1920s: reconciling atomic structure with quantum
mechanics and figuring out how protons and electrons, which at the
time were both presumed to be constituents of the nucleus,
cohabited. Cathcart focuses on the Cavendish Lab at the University
of Cambridge and in particular on John Cockcroft and Ernest Walton.
Cockcroft and Walton built a high-voltage particle accelerator to
give protons enough energy to penetrate the electrical barrier of
the nucleus and serve as a nuclear probe. In 1932 they found that
lithium nuclei bombarded with protons were splitting into two helium
nuclei, with an energy release equal to that calculated by
Einstein's famous equation, E=mc2. In
addition to producing the first artificial disintegration of an
atom, the Cockcroft-Walton experiment demonstrated the scientific
value of the particle accelerator, which went on to become the
primary tool (along with detectors) for nuclear and then particle
physics. It also won the two men the Nobel Prize for physics in 1951.
Cathcart is very good at sketching personalities. However, like many
writers of popular science, he does not always make clear where the
historical record leaves off and speculation begins, and he skirts
technical details, relying instead on an array of metaphors and
analogies. But he also highlights the driving force of scientific
curiosity, a feature often neglected in more scholarly work, and he
captures well the vexations of lab research—the tedious
breaking down and reassembling of balky apparatus, the patient
pursuit of vacuum leaks and background effects. He relies heavily on
the abundant reminiscences of the historical actors, although he
does take advantage of the recent opening of Walton's personal
papers too. Cathcart also highlights the role of George Gamow, whose
theory of quantum tunneling underpinned the experimental efforts to
sneak protons through the energy barrier. Finally, as the book's
subtitle indicates, Cathcart captures the sense of international
competition, in this case the race to high energy against Merle Tuve
at the Carnegie Institution, Charles Lauritsen at Caltech and
especially Ernest Lawrence at the University of California,
Berkeley. Why did the Cavendish get there first? Cathcart's answer:
the lab's preoccupation with the nucleus, starting with Rutherford
and expressed also in James Chadwick's discovery of the neutron.
But there is another reason the Cavendish won this race. A mythology
has grown up around the Cavendish approach to
experimentation—namely, that with hands-on inventiveness and
economy its scientists jury-rigged experiments out of string and
sealing wax, which then produced groundbreaking research. Cathcart's
narrative, if not the book's flyleaf, makes clear that Cavendish
scientists were far from "the last true gentlemen
scientists" tinkering on tabletops. On the contrary, their
equipment filled entire custom-built labs and depended on industrial
engineering expertise, and they tapped government funding and
developed organizational skills. As Cathcart notes, the
Metropolitan-Vickers firm (known as Metro-Vick) supplied
transformers, vacuum pumps and a new type of plasticine, and
Cockcroft himself had previously worked for Metro-Vick, as had other
Cavendish physicists; Cathcart could also have observed that the BTH
Company provided thyratrons for electronic particle counters. The
string-and-sealing-wax mythology has obscured the fact that the
Cavendish outpaced its American counterparts, including Berkeley, in
the initial integration of academic physics and industrial
engineering, or what came to be known as big science.
If this book is not about jury-rigging gentleman scientists, neither
is it exactly about the "greatest scientific discovery of the
age," as newspapers called it. The discovery of the neutron,
announced by Chadwick at the Cavendish scant months before the
Cockcroft-Walton results and also described briefly by Cathcart, was
probably more important to nuclear science: It made possible a
quantum field theory of a nucleus composed of protons and neutrons,
and it provided experimentalists with a new tool for provoking
nuclear disintegrations, because the neutron is not repelled by the
positive charge of the nucleus.
Cathcart rightly notes that it was not scientists but rather
journalists who seized on the Cockcroft-Walton results as the
"splitting of the atom" and hence as the first step toward
limitless energy, whether peaceful or not. Never mind that their
experiment had produced a number of discrete events, not a chain
reaction, and moreover that it consumed more energy than it
released. Cathcart has previously written on the British atomic-bomb
program, and he notes here that "Modern perceptions of what was
achieved in the Cavendish laboratory in 1932 are inevitably coloured
by the atomic bombs and the Cold War that followed." He denies
that the Cavendish physicists were driven by dreams of bombs or
reactors—and anyway, he notes, the neutron likewise proved
more crucial to the eventual detection and development of atomic
fission. But if this book is not about the last gentleman
scientists, or the central experiment of the age, or even the
initial step on the path to Hiroshima, it does show how intellectual
curiosity led physicists simultaneously into the nucleus, into new
partnerships with industry and into new modes of research.
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