In the USSR Pontecorvo was welcomed with honours and given a number of privileges reserved only to the Soviet nomenklatura. He worked until his death in what is now the Joint Institute for Nuclear Research (JINR) in Dubna, concentrating entirely on theoretical studies of high energy particles and continuing his research on neutrinos and decay of muons. In recognition of his research he was awarded the Stalin Prize in 1953, membership in the Communist Party of the Soviet Union in 1955 and the Soviet Academy of Sciences in 1958, and two Orders of Lenin. He was awarded the Lenin Prize in 1964 for his work on the weak interaction. He began a lifelong affair with Rodam Amiredzhibi, the wife of poet Mikhail Arkadyevich Svetlov, in 1950. In 1955, he appeared in public at a press conference where he explained to the world the motivations of his choice to leave the West and work in the Soviet Union. As a result, the United Kingdom revoked his British citizenship on 24 May 1955. Pontecorvo was not permitted to leave the Soviet Union for many years; his first trip abroad being in 1978 when he travelled to Italy for celebrations of Amaldi's 70th birthday. Thereafter, he made frequent trips to Italy, and occasional visits to other countries. France refused to allow him to visit in 1982 and 1984, but relented in 1989.