At that time the cyclotron in Berkeley was among the first to produce useful amounts of radioactive isotopes which could be used in studies of their effects on living tissue.

Concern was expressed over the safety of Manhattan Project laboratory personnel working with newly isolated plutonium in 1944.

[4] Three teams headed by Hamilton, Louis Hempelmann and Wright Haskell Langham carried out trials, injecting plutonium into 18 unsuspecting human patients and measuring its concentration in excreta.

[5] Hamilton's studies of isotope retention in humans, especially of radioactive strontium and the transuranic elements, were the principal reason for the U.S. Atomic Energy Commission setting of far lower tolerance limits of these substances than had been theorised before trials.

Hamilton wrote that large primates like "chimpanzees ... [should] be substituted for humans in the planned studies on radiation's cognitive effects.

"[6] Eugene Saenger would be the one who carried out these experiments from 1960 to 1971 at the University of Cincinnati, exposing "at least 90 cancer patients to large radiation doses.