Half-Life: The Divided Life of Bruno Pontecorvo, Physicist or Spy by Frank Close Basic Books, 378 pp., $29.99

“I want to die as a great scientist, not as your fucked spy.” These words were spoken in Russian by Bruno Pontecorvo a year before his death in 1993, in reply to a Russian government official who was trying to arrange for a visiting historian to interview him. They come as close as Pontecorvo ever came to confirming the widespread belief that he had been spying for the Soviet Union when he was working at the Canadian nuclear reactor project in the 1940s.

The words vash jebanyi shpion describe the way he did not wish to be remembered. In Half-Life, his new biography of Pontecorvo, the particle physicist Frank Close translates them as “your fucking spy,” which misses the precise meaning. Pontecorvo was certainly aware of the precise meaning of the word when he used it. It describes his emotional reaction to the way he was treated by the Russians as well as by the Western media. It gives us a glimpse of the inner turmoil that he successfully concealed from his family and friends. He was undoubtedly a great scientist. Whether he was a spy is still open to question.

The following facts are not open to question. Pontecorvo was a brilliant young experimental physicist working with Enrico Fermi in Rome in the years 1934–1936. He helped Fermi to start a revolution in nuclear physics using slow neutrons as an experimental tool. The use of slow neutrons made it possible for the first time to produce nuclear transformations involving atoms of all kinds. One of the reactions that slow neutrons produced was the fission of uranium, a discovery that Fermi missed.

In 1936, when Mussolini joined Hitler in persecuting Jews, Pontecorvo, who was from a nonobservant Jewish family, moved to France and worked there with the husband-and-wife team Irène Curie and Frédéric Joliot. Curie and Joliot were prominent and passionate Communists. Pontecorvo joined the Communist Party and remained an apparently sincere believer in communism for the rest of his life. In 1940, when Hitler overran France, he escaped to the US and found a job with the Texas oil company Well Surveys, introducing the technology of neutron logging to the American oil industry. His experimental skills were precisely what were needed to find oil-bearing rock surrounding a drilled borehole.

In 1943 Pontecorvo was invited to join the Canadian nuclear reactor project at Chalk River. He worked there on reactors for six years. His work had nothing to do with bombs but was then classified as secret. In 1949 he moved to the British nuclear energy project at Harwell and continued to do secret work on reactors.

In the summer of 1950 he traveled with his wife Marianne and their three small sons for a holiday in Italy. After some weeks of apparently carefree hiking and…