Despite the restrictions on knowledge and materials of the Anglo-American nuclear monopoly in the early Cold War, Norway and the Netherlands managed to build and operate a joint nuclear reactor by July 1951. They were the first countries to do so after the Great Powers. Their success was largely due to the combination of the strategic materials of heavy water (Norway) and uranium (the Netherlands). Nonetheless, they had to overcome significant political and technical obstacles. In that process a number of specific nuclear secrets played a central role. This case is used to study how and why knowledge circulation was impeded by secrecy. Specifically, I will explore four different secrets that illustrate how the Netherlands and Norway, being outside the British and American secrecy regimes, chafed against those regimes. Knowledge circulation was enabled through relations within networks that were at the same time scientific, diplomatic, and personal. I will identify three main factors that affected the mobility of information: the availability of strategic nuclear materials, the scientists’ individual interactions, and national interests.

The composition of the aurora borealis became a subject of scientific interest with the introduction of spectroscopy, but for a long time the aurora refused to reveal its secrets. After fifty years of research, the origin of the dominant green line of wavelength 5577 ÅÅ was still a mystery. Only in 1912 did progress finally begin to occur in the understanding of the aurora, a field of research which appealed in particular to Norwegian scientists. Prominent among them was Lars Vegard (1880––1963), who in 1923 suggested a new picture of the upper atmosphere and an explanation of the green line in terms of excitations of frozen nitrogen dust particles. Although apparently confirmed by cryogenic experiments, Vegard's theory was challenged by the Canadian physicist John McLellan (1867––1935) who in 1925, together with his postdoctoral student Gordon Shrum (1896––1985), reproduced the line in experiments with helium-oxygen mixtures. This is the story of how the enigma of the green auroral line was finally resolved and explained by the quantum theory of atoms, namely as a transition between two metastable states of oxygen. It is also the story of two of the period's leading specialists in auroral spectroscopy, their rivalry, and different approaches to the study of the northern light.