Cahn left Cambridge in 1947 to take up a research post at Harwell Atomic Energy Research Establishment with a salary that enabled him to get married. He completed his doctoral research without supervision, Orowan rarely wrote up the work of his doctoral students and Cahn finally wrote it up alone in 1949. At Harwell, Robert continued his researches into the process of "deformation twinning" Crystal twinning where he demonstrated a new type of twinning in uranium crystals. However, as the only person undertaking fundamental research,at Harwell, Cahn felt isolated and in 1951 he moved to Birmingham to the Department of his father in law, Daniel Hanson. Here he supervised research students concentrating on twinning, intermetallics and the formation of crystal nuclei during recrystallisation. These themes remained the centre of Cahn's attention for the remainder of his academic life.