The development of global networks of radioactivity monitoring, initially established for military surveillance by Cold War superpowers in late 1940s, had a critical turning point in mid 1950s. International controversy on the effects of atmospheric nuclear tests in human health, led the United Nations to establish a Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). The history of this institution, constituted by scientific experts from fifteen nations, shows the different diplomatic strategies and intelligence techniques put in place to control the scientific debate in the committee and its public image, as well as the interactions among scientists that led to the formation of a transnational network with pretensions of objectivity and political independence. The dynamics and networks put in place in this area may have provided a model to later institutions focusing on environmental data collection and the evaluation of its impact on the health of human populations.