For the last half of the 20th century cobalt-60 units were the mainstay of radiation treatments for cancer. This book describes the development of the first cobalt -60 unit in the United States and the man behind it, Leonard Grimmett. Conceptually conceived before World War II it only became possible because of the development of nuclear reactors during the war. The initial idea was to replace the radium in the contemporary units of the time with cobalt-60, but with the realization that the reactors could produce much more cobalt-60 than originally thought the design of the cobalt-60 unit was drastically changed to take advantage that the application of the inverse square law to cancer radiation treatments would make. Although Grimmett conceived of and published his ideas first, the Canadians built the first units because of the capability of their reactor to produce more suitable cobalt-60 sources. The story tells how Grimmett and the other people involved came together at the time that the U S Atomic Energy Agency was pushing the use of radioactivity in medicine. But Grimmett died suddenly before his unit could be built and very little information about him was known until recently when various documents have come to light, allowing the full story to be told.