of a number of neutrons emitted from a source". He also worked on several official bodies connected with nuclear physics, and arranged the Atom Train, a major travelling exhibition for schools on civil nuclear energy. At St Bartholomew's, Rotblat worked on the effects of radiation on living organisms, especially on ageing and fertility. This led him to an interest in nuclear fallout, especially strontium-90 and the safe limits of ionising radiation. In 1955, he demonstrated that the contamination caused by the fallout after the Castle Bravo nuclear test at Bikini Atoll by the United States had been far greater than that stated officially. Until then the official line had been that the growth in the strength of atomic bombs was not accompanied by an equivalent growth in radioactivity released. Japanese scientists who had collected data from a fishing vessel, the Lucky Dragon, which had inadvertently been exposed to fallout, disagreed with this. Rotblat was able to deduce that the bomb had three stages and showed that the fission phase at the end of the explosion increased the amount of radioactivity by forty times. His paper was taken up by the media and contributed to the public debate that resulted in the ending of atmospheric tests by the Partial Nuclear Test Ban Treaty. Peace work Rotblat believed that scientists should always be concerned with the ethical consequences of their work. He became one of the most prominent critics of the nuclear arms race, was the youngest signatory of the Russell–Einstein Manifesto in 1955, and chaired the press conference that launched it. After the positive coverage of the manifesto, Cyrus Eaton offered to fund the influential Pugwash Conferences on Science and World Affairs, an international organisation that brought together scholars and public figures to work toward reducing the danger of armed conflict and to seek solutions to global security threats, particularly those related to nuclear warfare. With Bertrand Russell and others, Rotblat organised the first of these in 1957 and continued to work within their framework until his death. In 1958, Rotblat joined the executive committee of the newly launched Campaign for Nuclear Disarmament (CND). Despite the Iron Curtain and the Cold War, he advocated establishing links between scientists from the West and East. For this reason, the Pugwash conferences were viewed with suspicion. Initially the British government thought them little more than "Communist front gatherings". However, he persuaded John Cockcroft, a