Between 1945 and 1947, 18 people were injected with plutonium, six with uranium, five with polonium, and at least one with americium by the Manhattan Project medical team. Only one of the subjects signed a consent form. The rest had no idea what was being injected into them. Reports show that many of the low-level physicians themselves were unaware of the exact substance they were injecting into patients.
These human subjects were essentially used as guinea pigs and calibration devices.
It was very important, you see. They needed to understand the dangers facing Manhattan Project workers and how to protect them. They were, of course, developing a weapon to eviscerate over 100,000 Japanese civilians. There is even evidence that Oppenheimer himself approved shipments of plutonium and uranium to be used for medical research.
During these experiments, the follow-up research was not thorough. Samples were contaminated or destroyed in transport on multiple occasions, and the ethical issues involved were essentially ignored.
The physicians involved knew that the procedures had no therapeutic benefits and would be detrimental in the long run if the patients lived. Human experimentation was justified because it was claimed that the patients were terminally ill; however, this was not true in all cases. Repeated errors in diagnosis, procedure, documentation, and research were made.
This was not known to the public until 30 years ago. US government covered up most of these radiation mishaps until 1993, when Clinton ordered a change of policy. Federal agencies then made available records dealing with human radiation experiments.