In subsequent years he collaborated with the Japanese physicist Yoshio Nishina who was in Copenhagen on an extended research visit and worked on the problem of Compton scattering of a Dirac electron.
Sa mga susunod na taon na siya collaborated sa Japanese pisisista Yoshio Nishina na sa Copenhagen sa isang pinalawak na pananaliksik bisitahin at nagtrabaho sa problema ng Compton scattering ng isang Dirac elektron.