Moving and other preliminaries kept Kurchatov busy until early 1943; in January the Navy even ordered him to Murmansk to work on German mines. The State Defense Committee (GKO) officially awarded him authority over the uranium project on February 11, 1943. “At that time it required special permission from the GKO to enter Moscow,” Kaftanov recalls. “We obtained permission for approximately a hundred people and a respective number of apartments and began inviting the chosen specialists.”
Working out of a room at the Moscow Hotel, on Marx Prospekt within sight of the Kremlin, Kurchatov assembled a core team of talents to prepare a feasibility study: theoretical physicists Georgi Flerov, Yuli Khariton and Yakov Zeldovich, experimentalists Isaak Konstantinovich Kikoin and Abram Alikhanov. Kikoin was a specialist in diffusion processes; Alikhanov, the young Academician and cosmic-ray expert, had competed with Kurchatov to head the project. Golovin:
In no hurry to expand his staff, [Kurchatov] tried to determine the main lines of attack and clearly formulate the scientific and engineering task ahead. He made numerous estimates and gave more detailed consideration to the possible ways of achieving a uranium fission chain reaction, carefully discussing them all. The group soon decided to build a [nuclear reactor] powered by [slow] neutron fission and simultaneously to work out means for separating large quantities of uranium isotopes… Kurchatov did not settle for half measures but at once boldly got started on estimates for a uranium bomb whose explosive power would come from fast-neutron fission, though he did not yet have so much as a microgram of pure U-235 and though neither he nor the other members of the group had an inkling as to the possibility of producing… plutonium —
At the beginning of 1943, that is, Igor Kurchatov and his colleagues in the Soviet Union were planning to build a nuclear reactor to prove that a chain reaction was possible in uranium and then to build a uranium bomb using U235 separated laboriously from natural uranium by physical means.
That would be a long, slow, expensive route to a bomb, one that Kurchatov certainly would not have chosen if he had known any shorter, faster and cheaper approach. The Soviet Union had only limited known reserves of uranium ore. It had only a few kilograms of heavy water and no facilities for making more, but a reactor moderated with heavy water would require several tons. It lacked the technology to make large quantities of pure graphite, an alternative to heavy water. It lacked the technology to make uranium metal or uranium hexafluoride. U235 had not yet been separated from U238 in the Soviet Union even at laboratory scale, and separating enough U235 for a bomb — tens of kilograms — would require developing a vast new industrial plant based on one or more new and difficult technologies. The gun bomb that Flerov had proposed and that Kurchatov had in mind would be prodigal of material, requiring several critical masses of U235 in its design.
The Soviet scientists had not yet appreciated that a reactor would transmute a portion of its larger inventory of U238 into a new man-made element heavier and less stable than uranium. Early in 1941, a team of American scientists at Berkeley led by radiochemist Glenn T. Seaborg had transmuted the first millionth of a gram of the new element in the big sixty-inch Berkeley cyclotron; the team had isolated the first sample on March 28, but the discovery was classified and would not be announced until after the war. In 1942, Seaborg had named the new element plutonium. By then, the Americans had determined what the Soviets did not yet know: that plutonium was even more fissionable than U235, with a fission cross section for fast neutrons 3–4 times as large as natural uranium. Since it could be separated chemically from the matrix of natural uranium in which it was bred, and since chemical separation was a far less difficult and therefore less costly process than physical separation, plutonium would probably be a shortcut to a bomb. So the leaders of the American program had come to believe. As a result, the Manhattan Project was now gearing up to breed plutonium in graphite and heavy-water reactors as well as to separate U235 using gaseous diffusion, thermal diffusion and electromagnetic means. A new secret laboratory that would open its doors on a mesa in the northern New Mexico wilderness in April 1943 would begin developing gun designs for both uranium and plutonium.
With its high priority and unlimited resources, the American program could afford to hedge its bets. At that early point in any case it would be prudent to explore alternatives, as Kurchatov also understood — when Ukrainian physicist Anatoli Petrovich Alexandrov asked him why he wanted thermal diffusion explored when there were better methods and it wouldn't be used, Kurchatov shot back, “The Devil knows what will be used. We have to try this way just in case.” But given a choice, a country with fewer resources might do better to give priority to plutonium. As of early 1943, Igor Kurchatov was evidently not aware of the existence of such a choice.
Then he saw the accumulated NKVD espionage. “He said he still had a lot to clear up,” Molotov remembers. “I decided then to provide him with our intelligence data. Our intelligence agents had done very important work. Kurchatov spent several days in my Kremlin office looking through this data… I asked him, ‘So what do you think of this?’ I myself understood none of it, but I knew the material had come from good, reliable sources. He said, ‘The materials are magnificent. They add exactly what we have been missing.’”
On March 7, 1943, Kurchatov finished drafting a fourteen-page review for Mikhail Pervukhin of the documents and transmissions that Moscow Center had collected. He only refers to British material — most of it probably passed by Klaus Fuchs — which almost certainly means that no American technical information had yet come in. But the British knew enough, and Kurchatov learned enough, to transform the Soviet program.
“Having reviewed the material,” Kurchatov began directly, “I came to the conclusion that it is of immense value for our science and our country. Its value cannot be overestimated.”
The material “shows what serious and intensive research and development work on the uranium problem has been undertaken in England,” Kurchatov explained. It also, he wrote, “provides some quite important reference points for our research, informing us of new scientific and technical approaches and enabling us to skip labor- intensive phases of development.”
Kurchatov judged at that point that the most valuable information in the espionage material dealt with isotope separation. The Anglo-American preference for gaseous diffusion as a means of separating U235 from U238 was unexpected, he explained; the Soviet scientists had believed the centrifuge approach to be much more promising. The espionage material “made us include diffusion experiments in our plans along with centrifuge.”
Next Kurchatov went through the theoretical work on diffusion, “a very detailed study.” Fuchs and Peierls had done that study and Fuchs later admitted passing a number of reports on diffusion theory to Alexander and to Sonia. The study provided a complete description of Franz Simon's proposed gaseous-diffusion unit. “Our theoreticians haven't yet checked this extensive work,” Kurchatov reported to Pervukhin, “but as far as I can judge, it is the work of a group of prominent scientists who based their well-founded and laborious calculations on clear physical principles.” The study was so complete, Kurchatov exulted, that it would enable his team “to skip the initial stage” and to move immediately to developing gaseous diffusion in the Soviet Union.
Kurchatov wanted further information on the machinery the British were developing for gaseous diffusion. He included five questions on the subject in this section of the report, clearly intending for Pervukhin to pass them to the NKVD and GRU to guide further espionage. The scientific director of the Soviet program to build an atomic bomb, that is, was not a passive recipient of espionage materials but an active participant in an extensive program of espionage directed against his country's wartime allies, Britain and the United States. On the other hand, they were allies that had decided to exclude his suffering country from a secret joint program to develop a decisive new weapon of war; he surely felt justified.
The material Kurchatov reviewed contained brief analyses of the usefulness of thermal diffusion, centrifuge and mass-spectrographic approaches to isotope separation. Thermal diffusion he discounted as “inefficient because of high energy consumption.” It was, but it would save the American project in 1944 when problems in barrier development delayed start-up of the big gaseous-diffusion plant under construction at Oak Ridge, Tennessee. The British analysis dismissed the centrifuge approach because of the difficulty of making a centrifuge that would hold together at the high rate of rotation necessary for isotope separation. “This conclusion may be challenged,” Kurchatov writes, defending the primary approach of the Soviet program so far. It would not be successfully challenged in the Soviet Union until long after the end of the war.
Kurchatov headed the second section of his March 7, 1943, report “The Problems of Nuclear Explosion and Chain Reaction.” Here were more revelations from espionage, first of all “the statement that it is possible to realize a nuclear chain reaction in a mixture of regular uranium oxide (or metallic uranium) and heavy water. For Soviet scientists this conclusion is unexpected and contradicts the established point of view; we considered it to be proven that without isotope separation it is not possible to achieve a chain reaction with heavy water.”
In 1940, misled by the cross-section estimate that Borst and Harkins had reported in their letter to the
