graphite pile was, and is, located, and where a small-scale heavy water pile had also been constructed.” Nunn May visited Chicago again in late August, Groves wrote, “conferring with officials of the Chicago Laboratory on the construction and operation of the Argonne pile and the proposed Montreal pile.” On a third and last visit, Groves writes, for the entire month of October 1944, “he carried on extensive work in collaboration with our scientists in a highly secret and important new field.” By then, Groves concluded, “May had spent more time and acquired more knowledge at the Argonne than any other British physicist.” Groves barred further visits because he felt Nunn May, as a member of the British Mission, knew as much as he ought to know about “later developments.”
The “highly secret” work in which Nunn May participated concerned making an atomic bomb using an isotope of uranium, U233, which is even rarer than U235 but which can be transmuted from thorium, element 90, a soft, silvery radioactive metal discovered in Sweden in 1829 and available for refining from monazite sand, of which there were major deposits in Brazil and North and South Carolina. If U233 proved to be bomb material, it could be bred from thorium in a nuclear reactor much as plutonium was being bred from U238, and like plutonium it could then be chemically separated from its parent matrix much more easily than U235 could be physically separated from U238.[16] Nunn May worked with the American experimental physicist Herbert Anderson in October 1944 trying to determine U233's cross sections for fission. The two physicists used foils of U233 for their cross-section measurements, foils that were extremely rare at the time because the U233 had to be transmuted laboriously in a cyclotron.
Groves thought Nunn May at Argonne had probably learned about the important phenomenon of reactor poisoning, discovered during the startup of the first big production reactor at Hanford late in September 1944. There is Soviet evidence from the postwar period that the British physicist either did not know of reactor poisoning or did not communicate the information to Soviet intelligence. Other significant Nunn May contributions, however, were yet to come.
Bruno Pontecorvo, handsome as a movie star, was an Italian protege of Enrico Fermi, one of Fermi's young, vigorous Rome group which had systematically worked its way through the periodic table in the mid-1950s bombarding the elements with neutrons to identify artificial radioactivities and had barely missed discovering nuclear fission. Pontecorvo, who was Jewish, had escaped France at the time of the German invasion and had found passage through Lisbon to New York. He joined the Anglo-Canadian research group in Montreal in 1943. He was an exceptional physicist, and made himself an expert on heavy-water reactors.
Donald Maclean arrived in New York on May 6,1944. He was married now, to an American woman named Melinda; his wife was pregnant with their second child and traveled with him. “He is six foot tall,” she had described him in a letter to her mother in 1940, when he was courting her in France, “blonde with beautiful blue eyes, altogether a beautiful man.” But even then Maclean was drinking too much, partly in response to the stress of his double life; if he had to have a “drinking orgy,” Melinda wrote him at that time in concern, “why don't you have it at home — so at least you will be able to get safely to bed?” Harry Gold and Klaus Fuchs also found release in periodic bouts of heavy drinking.
Maclean had served as third secretary at the British Embassy in Paris from September 1938 until the fall of France, in the midst of which he and Melinda had married; they had escaped to England on a tramp steamer. Back in London in wartime, Maclean was stuck in the Foreign Office General Department, bored with matters of shipping, supply and economic warfare, until he left for the United States. Throughout the war he continued his work of espionage. His control, Anatoli Gorsky, attache and then second secretary at the Soviet Embassy in London, also controlled Anthony Blunt. Blunt had found his way into MI5, the British FBI. In 1940, Maclean met twice with Kim Philby, who had lost contact with his Soviet control. Maclean arranged a renewed connection. Philby, who had worked as a freelance correspondent in Spain during the Spanish Civil War, was beginning his remarkable career in British counterintelligence as a propaganda expert for the Special Operations Executive (SOE), the British counterpart to the US Office of Strategic Services (OSS), the predecessor to the Central Intelligence Agency. By the time Maclean left for the US, Blunt had become responsible for the security of the various governments in exile in London. Philby directed the Iberian section of the counterespionage branch of MI6, the British CIA.
Maclean shipped for America to work at the British Embassy in Washington as a member of the joint Anglo- American secretariat of the Combined Policy Committee (CPC). The CPC had been established at the 1943 Quebec Conference between Winston Churchill and Franklin Roosevelt to facilitate British, US and Canadian collaboration on the atomic bomb. One of its first results was the transfer to the United States of the group of British scientists that included Klaus Fuchs. Another result, which James Chadwick had recommended, would be the development of the Chalk River heavy-water reactor.
Under the CDC, a subordinate body known as the Combined Development Trust (CDT) had taken over work that General Groves had begun late in 1942 buying up rights to corner the world market in high-grade uranium and thorium ores. For Groves, ore was fundamental. Control the supply of high-grade ore, he believed, and other countries, the Soviet Union in particular, could not build atomic bombs. Groves's organization, code-named the Murray Hill Area, had reviewed some 67,000 volumes, more than half in foreign languages, reporting occurrences of uranium ores, had developed the first lightweight, portable Geiger counters for field investigation, had sent out geologists to explore ore fields in the US and abroad and had completed fifty-six geological reports covering more than fifty countries. Groves reported to Secretary of War Henry Stimson on behalf of the CDT in late November 1944 that the US and Britain would control more than 90 percent of the world supply of high-grade uranium ore if Belgium gave them exclusive rights to the output of its Shinkolobwe mine in the Belgian Congo. Before the end of the war, the Belgians agreed. The Soviet Union, the Murray Hill Area investigators had concluded, had only “medium-grade ore. [A] few hundred tons’ production. Potential possibilities could be great.”
Donald Maclean was in position to communicate such high-level policy information to the Soviet Union. By the time he transferred to Washington, the NKVD had assigned atomic-bomb espionage first priority; Maclean made contact with Anatoli Yatzkov, and would frequently travel to New York to deliver information. If Stalin needed evidence that the nations that called themselves his allies were colluding against him to deny him nuclear weapons while they built up an arsenal, Donald Maclean could supply it. Someone did; a discussion of “the question of the existence and reserves of uranium deposits” and who controlled them turned up in a general NKVD review of Anglo-American bomb development that went to Beria on February 28,1945.
Nor was the Soviet Union the only country interested in knowing more about American work on the atomic bomb. The work had started in Britain, the British were US allies and had shared their secrets freely, but it was US policy to restrict and compartmentalize British access to American research and development. Thus, for example, General Groves refused to authorize revealing to scientists in Canada the process that Glenn Seaborg and his coworkers at the University of Chicago had developed for separating and purifying plutonium. “As a gesture in their direction,” the official Manhattan Project history reports, straight-faced, “Groves agreed to permit a limited amount of irradiated uranium in the form of slugs from [Oak Ridge] to go to Montreal so that the group there could work out independently the methods of plutonium separation and purification.” Similarly, Fuchs had not been told that a full- scale gaseous-diffusion plant was under construction in Tennessee.
But the British had decided, probably before their scientific team left England, that they would have to develop their own atomic bomb after the war. John Anderson, who directed British Tube Alloys Research, said as much to the scientists on his staff in January 1944. “We simply could not acquiesce in an American monopoly on this development,” postwar British Foreign Minister Ernest Bevin would write. Churchill told Roosevelt of the British decision in February 1945, which raises the interesting question of the extent to which US political leaders tacitly endorsed the British project. When Rudolf Peierls moved to Los Alamos to direct the British group there, James Chadwick asked Peierls to keep him informed:
I therefore wrote letters at regular intervals in which I summarized, to the best of my knowledge, what was going on. I was a little doubtful about the appropriateness of this, because no secret information was supposed to be sent out from the laboratory without special permission…
Then one day Richard Tolman, a distinguished elder statesman of physics who assisted Groves… asked to see me, as he had a message from Groves. When he started, “I understand you have been writing letters to Chadwick about the work of the laboratory,” I felt that here my chickens were coming home to roost. But he continued, “General Groves finds that Chadwick is often better informed than he is, and wondered if he could have copies of your letters.” He added that, if these letters referred also to purely domestic problems of the British group I could of course omit the relevant passages from the copies for Groves. This made it clear that the intention was
