Atomic Physicist

By Richard Rhodes

If the 19th century was the century of chemistry, the 20th was the century of physics. The burgeoning science supported such transforming applications as medical imaging, nuclear reactors, atom and hydrogen bombs, radio and television, transistors, computers and lasers. Physical knowledge increased so rapidly after 1900 that theory and experiment soon divided into separate specialties. Enrico Fermi, a supremely self-assured Italian American born in Rome in 1901, was the last great physicist to bridge the gap. His theory of beta decay introduced the last of the four basic forces known in nature (gravity, electromagnetism and, operating within the nucleus of the atom, the strong force and Fermi's "weak force"). He also co-invented and designed the first man-made nuclear reactor, starting it up in a historic secret experiment at the University of Chicago on Dec. 2, 1942. In the famous code that an administrator used to report the success of the experiment by open phone to Washington, Fermi was "the Italian navigator" who had "landed in the new world."

He had personally landed in the new world four years earlier, with a newly minted Nobel Prize gold medal in his pocket, pre-eminent among a distillation of outstanding scientists who immigrated to the U.S. in the 1930s to escape anti-Semitic persecution in Hitler's Germany and Mussolini's Italy--in Fermi's case, of his Jewish wife Laura.

A dark, compact man with mischievous gray-blue eyes, Fermi was the son of a civil servant, an administrator with the Italian national railroad. He discovered physics at 14, when he was left bereft by the death of his cherished older brother Giulio during minor throat surgery. Einstein characterized his own commitment to science as a flight from the I and the we to the it. Physics may have offered Enrico more consolatory certitudes than religion. Browsing through the bookstalls in Rome's Campo dei Fiori, the grieving boy found two antique volumes of elementary physics, carried them home and read them through, sometimes correcting the mathematics. Later, he told his older sister Maria that he had not even noticed they were written in Latin.

He progressed so quickly, guided by an engineer who was a family friend, that his competition essay for university admission was judged worthy of a doctoral examination. By 1920 he was teaching his teachers at the University of Pisa; he worked out his first theory of permanent value to physics while still an undergraduate. His only setback was a period of postdoctoral study in Germany in 1923 among such talents as Wolfgang Pauli and Werner Heisenberg, when his gifts went unrecognized. He disliked pretension, preferring simplicity and concreteness, and the philosophic German style may have repelled him. "Not a philosopher," the American theorist J. Robert Oppenheimer later sketched him. "Passion for clarity. He was simply unable to let things be foggy. Since they always are, this kept him pretty active." He won appointment as professor of theoretical physics at the University of Rome at 25 and quickly assembled a small group of first-class young talents for his self-appointed task of reviving Italian physics. Judging him infallible, they nicknamed him "the Pope."

The Pope and his team almost found nuclear fission in 1934 in the course of experiments in which, looking for radioactive transformations, they systematically bombarded one element after another with the newly discovered neutron. They missed by the thickness of the sheet of foil in which they wrapped their uranium sample; the foil blocked the fission fragments that their instruments would otherwise have recorded. It was a blessing in disguise. If fission had come to light in the mid-1930s, while the democracies still slept, Nazi Germany would have won a long lead toward building an atom bomb. In compensation, Fermi made the most important discovery of his life, that slowing neutrons by passing them through a light-element "moderator" such as paraffin increased their effectiveness, a finding that would allow releasing nuclear energy in a reactor.

If Hitler had not hounded Jewish scientists out of Europe, the Anglo-American atom bomb program sparked by the discovery of fission late in 1938 would have found itself shorthanded. Most Allied physicists had already been put to work developing radar and the proximity fuse, inventions of more immediate value. Fermi and his fellow emigres--Hungarians Leo Szilard, Eugene Wigner, John von Neumann and Edward Teller, German Hans Bethe--formed the heart of the bomb squad. In 1939, still officially enemy aliens, Fermi and Szilard co-invented the nuclear reactor at Columbia University, sketching out a three-dimensional lattice of uranium slugs dropped into holes in black, greasy blocks of graphite moderator, with sliding neutron-absorbing cadmium control rods to regulate the chain reaction. Fermi, still mastering English, dubbed this elegantly simple machine a "pile."

The work moved to the University of Chicago when the Manhattan Project consolidated its operations there, culminating in the assembly of the first full-scale pile, CP-1, on a doubles squash court under the stands of the university football field in late 1942. Built up in layers inside wooden framing, it took the shape of a doorknob the size of a two-car garage--a flattened graphite ellipsoid 25 ft. wide and 20 ft. high, weighing nearly 100 tons. Dec. 2 dawned to below-zero cold. That morning the State Department announced that 2 million Jews had perished in Europe and 5 million more were in danger; American boys and Japanese were dying at Guadalcanal. It was cold inside the squash court, and the crowd of scientists who assembled on the balcony kept on their overcoats.

Fermi proceeded imperturbably through the experiment, confident of the estimates he had charted with his pocket slide rule. At 11:30 a.m., as was his custom, he stopped for lunch. The pile went critical in midafternoon with the full withdrawal of the control rods, and Fermi allowed himself a grin. He had proved the science of a chain reaction in uranium; from then on, building a bomb was mere engineering. He shut the pile down after 28 minutes of operation. Wigner had thought to buy a celebratory fiasco of Chianti, which supplied a toast. "For some time we had known that we were about to unlock a giant," Wigner would write. "Still, we could not escape an eerie feeling when we knew we had actually done it."

From that first small pile grew production reactors that bred plutonium for the first atom bombs. Moving to Los Alamos in 1944, Fermi was on hand in the New Mexican desert for the first test of the brutal new weapon in July 1945. He estimated its explosive yield with a characteristically simple experiment, dropping scraps of paper in the predawn stillness and again when the blast wind arrived and comparing their displacement.

Fermi died prematurely of stomach cancer in Chicago in 1954. He had argued against U.S. development of the hydrogen bomb when that project was debated in 1949, calling it "a weapon which in practical effect is almost one of genocide." His counsel went unheeded, and the U.S.-Soviet arms race that ensued put the world at mortal risk. But the discovery of how to release nuclear energy, in which he played so crucial a part, had long-term beneficial results: the development of an essentially unlimited new source of energy and the forestalling, perhaps permanently, of world-scale war.

Richard Rhodes is the Pulitzer-prizewinning author of The Making of the Atomic Bomb