importance.” He was surprised at the high probability for spontaneous fission in Pu240; it was “very important to receive additional information on these matters.”
The espionage material included a table of U235 and Pu239 fission cross sections for fast neutrons at various energies. “This table,” Kurchatov noted, “makes it possible to define reliable figures for the critical mass of the atomic bomb” and confirmed that “the formula given for the critical radius may be correct within 2 percent, as the text indicates.”
Kurchatov was puzzled at the accuracy of the cross-section measurements, since it implied that the US had access to large amounts of U235 and pluto-nium — which suggests that he was not yet aware that the Manhattan Project was now producing uranium and plutonium in kilogram quantities.
The larger part of the document concerned implosion, “about which,” Kurchatov wrote, “we have learned only recently and work on which we have only begun.” Yatzkov's eagerness to learn more from David Greenglass and then from Harry Gold about HE lenses presumably emanated from Moscow Center. “But already,” Kurchatov added, “the advantages of this method over the gun method are clear.”
Kurchatov briefly summarized the basics of implosion that the espionage document discussed. “All this is very valuable,” he went on, “but most essential are the indications of the conditions necessary to achieve a symmetric explosion. The material describes the interesting phenomena of irregularities in the detonation wave” — these were the troublesome jets which Fuchs had studied that formed where detonation waves collided and intersected — “and describes how these irregularities may be avoided by the proper distribution of detonators and by using interlayers of explosives with different actions” — “interlayers” meaning explosive lenses. “This part of the material also deals with important questions of techniques of experimenting with explosives and the optics of explosive phenomena.”
“Since research on implosion has not advanced much here,” Kurchatov concluded, “it is not possible yet to formulate questions [to guide espionage]. This can be done after serious analysis of the material.” Kurchatov suggested that a portion of the top secret text — “from page 6 to the end except for page 22” — should be shown to “Professor Khariton.” To a limited extent, then, Yuli Khariton was aware from at least spring 1945 that espionage was supplying significant input into the Soviet program.
Kurchatov's desire in mid-March for “several grams of highly-enriched uranium” was partly satisfied a month later when Alan Nunn May passed Lieutenant Angelov, in Nunn May's words, “a slightly enriched sample [of U235] in a small glass tube [consisting] of about a milligram of oxide.” Unlike Fuchs, Nunn May was willing to accept compensation; Angelov gave him two bottles of whiskey — a scarce luxury in wartime — and two hundred dollars.
The Red Army offensive against Berlin began in mid-April. Marshal Georgi Konstantinovich Zhukov directed the battle as he had directed the battles of Moscow and Stalingrad, and described it at a press conference immediately afterward:
I attacked along the
The great offensive was launched at 4 a.m. on April 16, and we devised some novel features: to help the tanks find their way, we used searchlights, 200 of them. These powerful searchlights not only helped the tanks, but also blinded the enemy, who could not aim properly at our tanks.
Very soon we broke through…
American and Soviet troops joined hands at Torgau, one hundred kilometers due south of Potsdam, a few days before Adolf Hitler's suicide on April 30. The Nazi dictator's personal staff burned his body in the garden of the
The day Berlin fell, a team of Soviet industrial managers and physicists flew in to Templehof airfield to explore German atomic-bomb research. Lieutenant General Avrami Pavlovich Zavenyagin, deputy director of the NKVD and the developer of the vast Magnitogorsk Steel Combine, led a group that included Lev Artsimovich, Isaak Kikoin and Yuli Khariton. The team established its headquarters in Berlin-Griinau. “A remnant of [German] scientists remained in Berlin and willingly talked to us,” Khariton recalls. “From these discussions it was clear to us that German progress along these lines had been slight. Kikoin and I told Zavenyagin what we'd gathered, and told him it would be prudent to find out whether the Germans had accumulated any stockpiles of uranium… It was entirely likely that uranium supplies in Belgium had been seized and taken out by the Germans. Zavenyagin approved of our idea and put an automobile at our disposal.”
In fact, a mixed British-American strike force led by Lieutenant Colonel John Lansdale, Jr., who was Groves's liaison officer with the British, had moved into what would soon be Soviet-occupied eastern Germany on April 17 to strip a Stassfurt factory of what Lansdale believed to be all the remaining Belgian Congo ore in Germany, 1,100 tons stored above ground in broken barrels. “The plant was a mess,” Lansdale reported to Groves, “both from our bombings and from looting by the French workmen… By the evening of 19th April we had a large crew busily engaged in repacking the material and that night the movement of the material to [the railhead] started.” Groves sent US Army Chief of Staff George Marshall a memorandum confirming the recovery on April 23. The Manhattan Project commander noted that in 1940 the German Army had confiscated “about 1200 tons of uranium ore” in Belgium, described Lansdale's operation, and concluded that “the capture of this material, which was the bulk of uranium supplies available in Europe, would seem to remove definitely any possibility of the Germans making use of an atomic bomb in this war.”
Now, two weeks later, the Soviet team was scouring the same ground. “Through our discussions with the German scientists,” says Khariton, “we discovered that there was a certain building in Berlin… where a card catalogue was kept with records of everything the Germans had plundered in the countries they'd occupied.” Such was Nazi greed that the card catalogue filled the six-story building. The catalogue staff refused to cooperate with the Soviet expedition. “After prolonged and excruciating attempts to get our bearings,” Khariton continues, “we managed to determine that there was in fact uranium oxide, but we couldn't come up with its location.” Then other, more cooperative Germans directed them to affiliated card catalogues in other cities. They went from city to city; eventually they found the uranium-oxide reference in a warehouse card catalogue. “But it turned out that some military personnel must have shipped it as a pigment — uranium oxide is, after all, bright yellow in color.” Finally they learned that a quantity of oxide had been sent to a tannery west of Berlin. The Soviet commander of that district told the physicists that the tannery was on American-occupied territory, but Khariton claims the tannery “turned out to be on our territory, right on the border with the American occupation zone”:
The tannery was in the control of an antifascist group. It was made up of workshops and warehouses, some of which were crammed with sheepskins, raw material awaiting production. In one of these last warehouses we came across a fair number of small wooden barrels. There was a scrap of cardboard on one of them with an inscription, U3Os. We sighed with relief. We informed Zavenyagin of our excursion, and arrangements were made for shipping the uranium oxide to the Soviet Union. The net quantity was in the vicinity of 130 tons.
Between the American team rushing to remove uranium ore from Soviet-occupied territory and the Soviet team rushing to remove the remaining ore from “right on the border” of American-occupied territory, the two operations accounted for all the Belgian Congo stock in Germany and about half the existing world supply. The American requisition became U235 for Little Boy; the Russian requisition, Kurchatov later told Khariton, “hastened the startup of the first [Soviet] industrial reactor for obtaining plutonium by about a year.” Such parallels seem enigmatic, but in fact the two bomb programs ran in parallel because the raw materials, the processing and the technology depended upon universal physical fundamentals that both sides could determine independently. At that basic level, there never was any “secret” of how to make an atomic bomb. Knowledge derived from espionage could only speed up the process, not determine it, and in fact every nation that has attempted to build an atomic weapon in the half-century since the discovery of nuclear fission has succeeded on the first try.
