Bruno Pontecorvo, right, with fellow physicist Carlo Franzinetti

The following is an extract from “Half Life, the divided life of Bruno Pontecorvo” the new book by the Oxford University physicist Frank Close, published by Oneworld. Pontecorvo was a prodigiously gifted physicist who, before the Second World War, worked with Enrico Fermi on the phenomenon of “slow neutrons”, work of fundamental significance in advancing the scientific understanding of matter. Pontecorvo went on to become an outstanding scientist in his own right, and during the war was at the heart of the Allied effort to harness nuclear energy. He worked on highly sensitive reactor projects in both Canada and Britain. After the war he settled in Britain, working at the Harwell nuclear research facility in Oxfordshire. Then in the summer of 1950, Pontecorvo and his family vanished.

Listen to Close discussing his book at a Prospect event:

“Did MI5 get back to you after I forwarded them your letter?”

The neat, handwritten note, on House of Lords stationery, was brief and to the point.When I received it, about two years into my research into the enigmatic life of physicist and possible spy, Bruno Pontecorvo, I had no idea that it would lead me to solve the mystery of his sudden disappearance at the height of the Cold War in 1950.

MI5 did get back to me: a file of “lost” papers regarding Pontecorvo had been “found.” The final entry in the MI5 record before Bruno Pontecorvo’s disappearance was a letter received on July 19, 1950, from the British embassy in Washington. The document, marked “SECRET,” appears to have had little impact. No action was taken in London. It would, however, lead to action in the Soviet Union. Once I saw the letter, the kaleidoscope of facts began to settle into a clearer picture.

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In the years immediately after World War II, the British embassy in Washington, DC, was the weak point of Western security. Unknown to the authorities, it played host to three members of the infamous Cambridge Five spy ring. From 1944 to 1948, one of these spies, Donald MacLean, exploited his position as the British representative on the American-British-Canadian council on the sharing of atomic secrets. He was, of course, privy to these secrets, and passed news about development of…

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