This large and comprehensive collection covers almost all aspects of Mitchell's professional career including his research, some in notebook form, from the early work under Rideal to his final clinical research project started in 1985. The bulk of the material relates to Mitchell's principal research activity--his effort to find a cure for cancer--and documents both his work as a scientist undertaking research into radiotherapeutic techniques and as a doctor treating patients with cancer, especially covering his years in the Department of Radiotherapeutics and Radiotherapeutic Centre, Addenbrooke's Hospital, the Medical School, and his lectures and courses. There is also documentation of Mitchell's extensive service for the Medical Research Council from 1946, sitting on numerous committees and panels to advise on radiation hazards and the medical applications of radiation and attending a number of the British-US-Canadian Tripartite Conferences on the uses of nuclear Energy, and of Mitchell's attendance at the first four United Nations Conferences on the Peaceful Uses of Atomic Power 1955, 1958, 1964, and 1971. Of special interest is material relating to early investigations of the sterilization by radiation of foodstuffs and medicines; extensive records relating to the development of the new Hills Road site for Addenbrooke's Hospital; as well as Medical School files which show the development of the Postgraduate Medical School and the establishment of the pre-graduate Clinical School. Included is comprehensive documentation of the establishment and work of the Anglo-German Medical Society of which Mitchell was a founder-member in 1959 and President of the British Section to 1968. Also represented are the International Union against Cancer, the Ministries of Health and Supply, and the World Health Organization. Correspondents include J.D. Cockcroft and G.C. de Hevesy.