Dr. Harold Elford Johns was one of the founders of medical physics. Trained in mathematics and physics, rather than medicine, early in his career he taught the practical aspects of radar and radio navigation to air force pilots, and tested aircraft castings with X-rays.

This practical orientation in physics led him to his life's work — the application of radiation in cancer therapy. He embarked on this path at the Physics Department of the University of Saskatchewan, where he established a program in medical physics that focused on X-ray radiation and radioactive isotopes for cancer treatment. The radiation research group worked on the problem of determining the appropriate doses of radiation and controlling the radiation during treatment.

Dr. Johns' most obvious achievement was the development of the cobalt-60 cancer therapy unit in 1951. The cobalt bomb, as it is known, revolutionized the treatment of cancers located deep in the body, where previous radiation therapies had proven ineffective. It has been estimated that seven million people have benefited from cobalt-60 therapy worldwide.