This dissertation is a social and technical history of radioactivity research in the 1920s, and of the emergence of nuclear physics in the 1930s. It is concerned with the production, circulation and certification of practice and knowledge in these fields of scientific research.

By 1914, the study of radioactivity was confined to a few centres - Paris, Berlin, Manchester and Vienna - possessing relatively large quantities of radium. The politics and organisation of this relatively closed network were irrevocably altered by the First World War. The election of Ernest Rutherford to the Cavendish Chair of Experimental Physics at Cambridge in 1919 brought radioactivity research, and a programme of Imperial physics, to the Cavendish Laboratory. Rutherford’s programme of research, based on his speculative nuclear model of the atom (1911), sought to map the internal topography of the atomic nucleus by means of scintillation counting experiments. Rutherford’s work on artificial disintegration, combined with F.W. Aston’s elucidation of the isotopes of the light elements by means of the mass-spectrograph, brought about a profound change in physicists’ and chemists’ views of atomic architecture.

In the early 1920s, as laboratories in Europe recovered from the war, the work of the Cavendish Laboratory was unchallenged. During the 1920s, as other laboratories entered the field of nuclear research, however, a series of controversies brought into question the reliability of the scintillation technique and the integrity of all experimental results based upon it. The foundational data yielded by the mass-spectrograph, too, were contested, occasioning a ‘crisis of certitude’ in radioactivity research, and prompting a redistribution of trust into alternative sources of experimental evidence - electronic (Geiger) counters and cloud chambers. The crediting of these techniques (which proved to be as problematic as those they ostensibly replaced) opened up new kinds of problems to experimental investigation.

In virtue of the new kinds of skills now required in the laboratory, a re-definition of the investigative community accompanied technical innovation. In the wake of a prolonged controversy between Cambridge and Vienna, a conference was convened at the Cavendish Laboratory in 1928, as a direct result of which researchers in several other European laboratories (including Maurice de Broglie and the Joliot-Curies in Paris, Bothe in Berlin and Pose at Halle) entered the field of nuclear research, multiplying the number of sites at which the new techniques were deployed. Theoretical physicists like George Gamow, too, began to apply the novel methods of wave mechanics to nuclear problems, gradually transforming the bounds of the possible and the plausible in nuclear research.

A reconfigured network of embodied practice gradually crystallised around the development of these material and conceptual technologies. This network - including laboratories and researchers in Cambridge, Paris, Berlin, Rome, Vienna, New York, Berkeley and Washington D.C. - embodied the emergent discipline of ‘nuclear physics.’ Chadwick’s disclosure of the ‘neutron’ in 1932 using the new experimental techniques ratified this social and technical re-alignment. The emergence of Nuclear Physics as a recognised discipline by 1934 was thus the simultaneous certification of a new regime of practice, a new sociopolitical network of laboratories and a new ontology.