Джеймс Глик - Genius - The Life and Science of Richard Feynman

“ Keep hanging on, ” he wrote. “ Nothing is certain. We lead a charmed life. ”

In the midst of their private turmoil came V-E day and then Richard’s twenty-seventh birthday. Arline had prepared another mail-order surprise: the laboratory was flooded with newspapers—handed about and tacked to wal s—proclaiming with banner headlines, “Entire Nation Celebrates Birth of R. P. Feynman!” The war in Europe, having provided so many of the scientists with their moral purpose, had now ended. The bloody circle was closing in the Pacific. They needed no threat of a German or Japanese bomb to urge them onward. Uranium was arriving. There would be one test—one last experiment.

At the Mayo Clinic in Minnesota another kind of experiment was under way, the first clinical trial of

streptomycin, a substance that had been discovered nearly two years before, in August 1943. The population participating in the trial: two patients. Both had been near death from tuberculosis when the experiment began in the fal of 1944; both were improving rapidly. Even so, it was not until the next August that the Mayo trial had expanded to as many as thirty patients. The doctors could see lesions healing and lungs clearing. A year after that, the study of streptomycin as an antitubercular agent had become the most extensive research project ever devoted to a drug and a disease. Researchers were treating more than one thousand patients. In 1947 streptomycin was released to the public.

Streptomycin’s discovery, like penicil in’s a few years earlier, had been delayed by medicine’s slow embrace of the scientific method. Physicians had just begun to comprehend the power of control ed experiments repeated thousands of times. The use of statistics to uncover any but the grossest phenomena remained alien. The doctor who first isolated the culture he named Streptomyces griseus , by cultivating some organisms swabbed from the throat of a chicken, had seen the same microbes in a soil sample in 1915 and had recognized even then that they had a tendency to kil disease-causing bacteria. A generation had to pass before medicine systematized its study of such microbes, by screening them, culturing them, and measuring their antibiotic strengths in careful y labeled rows of test tubes.

Nuclear Fear

In its infancy, too, was the branch of science that would have to devote itself to the safety, short-term and long-term, of humans in the presence of nuclear radiation. The sense of miasmic dread that would become part of the cultural response to radioactivity lay in the future. The Manhattan Project’s researchers handled their heavy new substances with a breeziness that bordered on the cavalier. Workers handling plutonium were supposed to wear coveral s, gloves, and a respirator. Even so, some were overexposed. The prototype reactors leaked radioactive material. Scientists occasional y ignored or misread their radiation badges. Critical-mass experiments always flirted with danger, and by later standards the safety precautions were flimsy. Experimentalists assembled perfect shining cubes of uranium into near-critical masses by hand. One man, Harry Daghlian, working alone at night, let slip one cube too many, frantical y grabbed at the mound to halt the chain reaction, saw the shimmering blue aura of ionization in the air, and died two weeks later of radiation poisoning.

Later Louis Slotin used a screwdriver to prop up a radioactive block and lost his life when the screwdriver slipped. Like so many of these worldly scientists he had performed a faulty kind of risk assessment, unconsciously mis-multiplying a low probability of accident (one in a hundred? one in twenty?) by a high cost (nearly infinite).

To make measurements of a fast reaction, the

experimenters designed a test nicknamed the dragon experiment after a cool y ominous comment of Feynman’s that they would be “tickling the tail of a sleeping dragon.” It required someone to drop a slug of uranium hydride through a closely machined ring of the same substance.

Gravity would be the agent in achieving supercriticality, and gravity, it was hoped, would carry the slug on through to a safe ending. Feynman himself proposed a safer experiment that would have used an absorber made of boron to turn a supercritical material into a subcritical one.

By measuring how rapidly the neutron multiplication died out, it would have been possible to calculate the multiplication rate that would have existed without boron.

The arithmetical inference would have served as a shield. It was dubbed the Feynman experiment, and it was not carried out. Time was too short.

Los Alamos hardly posed the most serious new safety chal enges, for al its subsequent visibility. These belonged to the vast new factory cities—Oak Ridge, Tennessee, and Hanford, Washington—where plants thrown up across thousands of acres now manufactured uranium and plutonium in bulk. Compounds and solutions of these substances were accumulating in metal barrels, glass bottles, and cardboard boxes piled on the cement floors of storerooms. Uranium was combined with oxygen or chlorine and either dissolved in water or kept dry. Workers moved these substances from centrifuges or drying furnaces into cans and hoppers. Much later, large epidemiological studies would overcome obstacles posed

by government secrecy and disinformation to show that low-level radiation caused more harm than anyone had imagined. Yet the authorities at the processing plants were overlooking not only this possibility but also a more immediate and calculable threat: the possibility of a runaway, explosive chain reaction.

Feynman had seemed to be everywhere at once as the pace of work accelerated in 1944 and 1945. At Tel er’s request he gave a series of lectures on the central issues of bomb design and assembly: the critical-mass calculations for both metal and hydride; the differences between reactions in pile, water boiler, and gadget; how to compute the effects of various tamper materials in reflecting neutrons back into the reactions; how to convert the pure theoretical calculations into the practical realities of the gun method and the implosion method. He became responsible for calculating the way the efficiency of a uranium bomb would depend on the concentration of uranium 235 and for estimating safe amounts of radioactive materials under a variety of conditions. When Bethe had to assign theorists to G Division (Weapon Physics Division—G for gadget) he assigned Feynman to four different groups. Furthermore, he let Oppenheimer know that, as far as the implosion itself was concerned, “It is expected that a considerable fraction of the new work coming in wil be carried out by group T-4

(Feynman).” Meanwhile, though Feynman was official y only a consultant to the group handling computation by IBM

machines, Bethe decreed that Feynman would now have

“complete authority.”

At Oak Ridge, where the first batches of enriched uranium were accumulating, a few officials began to consider some of the problems that might arise. One letter that made its way to Los Alamos from Oak Ridge opened,

“Dear Sir, At the present time no provisions have been made in the 9207 Area for stopping reactions resulting from the bringing together by accident of an unsafe quantity of material… .” Would it make sense, asked the writer—a plant superintendent with the Tennessee Eastman Corporation—to instal some kind of advanced fire-extinguishing

equipment,

possibly

using

special

chemicals? Oppenheimer recognized the peril waiting in such questions. He brought in Tel er and Emilio Segrè, head of the experimental division’s radioactivity group.

Segrè paid an inspection visit, other theorists were assigned, and final y the problem was turned over to Feynman, with his expertise in critical-mass calculations.