needed. In August 1943, Churchill and Roosevelt negotiated the Quebec Agreement, which resulted in a resumption of cooperation between the United States and Great Britain, merging Tube Alloys into the Manhattan Project. John Cockcroft became director of the Montreal Laboratory in 1944. For safety reasons, he decided to build the reactor at the remote Chalk River Laboratories. With an eye on a post-war nuclear program, he had Pontecorvo and Alan Nunn May "debrief" Manhattan Project scientists who visited Canada, in practice spying for Britain. Unfortunately, Nunn May was also a Soviet spy. Pontecorvo's second son was born on 20 March 1944, and was named Tito after the Yugoslavian communist leader. A third son, Antonio, was born in July 1945. With heavy water supplied by the United States, the reactor at Chalk River, known as ZEEP went critical on 5 September 1945. In addition to reactor design, Pontecorvo also looked into cosmic rays, the decay of muons, and what would become his obsession, neutrinos. He wrote 25 papers related to reactor design, although only two were published. He also did some prospecting with his old firm, searching for uranium deposits near Port Radium in the Northwest Territories. Physicists were in great demand after the war ended in August 1945, and Pontecorvo received attractive and lucrative offers from several universities in the United States. Instead, on 21 February 1946, he accepted an offer from Cockcroft to join the British Atomic Energy Research Establishment (AERE). For the time being, he remained at Chalk River for the commissioning of the new NRX reactor in 1947. He was one of four physicists present in the control room when the NRX was started up on the night of 21–22 July 1947. At the time, it had five times the neutron flux of any other reactor, and was the most powerful research reactor in the world. He acquired the nickname "Ramon Novarro" after the actor of that name following an adventure in which he made a trip to Boston with two women, which culminated in Marianne clearing out the bank account and departing for Banff with the children; but they were reconciled. Although he had previously taken steps to become a United States citizen, he instead became a British subject on 7 February 1948. He finally departed Chalk River for the United Kingdom on 24 January 1949. Defection At Harwell, Pontecorvo continued to be involved in reactor