In 1970, surgeons in Paris implanted the first nuclear-powered pacemaker, and over the next five years, at least 1,400 additional people received the devices, mostly in France and the United States. Encased in titanium, the batteries for these devices contained a radioactive isotope—typically about a tenth of a gram of plutonium-238—and could operate for decades without maintenance. The invention provided relief to a population of people who previously needed surgery every few years to change ou...