Radium–the Benchmark for Alpha Emitters

States have handled plutonium. Of those workers, only about fifty, all from the nuclear-weapons complex, have been exposed to plutonium at levels above the maximum permissible dose. Because so few people have high-dose exposures, we have little direct information about the risk of plutonium in man. This leads to the ironic situation that the better we protect our workers, the less we know about their risk. What then do we use to base our decisions about the risk of plutonium and the precautions we need to take to safeguard workers against that risk? Much of our understanding of the health risk posed by plutonium is based on another element, radium. Like plutonium, radium is an alpha-emitting radioisotope, but it is created naturally as a decay product, or daughter, of uranium. As described below, thousands of people were exposed to radium before 1932, and the effects of the many high-dose exposures became apparent after just a few years. That grievous situation none-the-less provided scientists with a group of people who were exposed internally to an alpha-emitting radioisotope, and who could be observed, evaluated, and studied. In 1944, the risk associated with the new manmade element plutonium was therefore estimated by scaling the risks associated with radium. That initial estimate was soon modified to take into account new animal data on the comparative toxicity and distribution in the bone of radium versus plutonium. But even today, much of our understanding of the risk of plutonium to humans and much of the public's perceptions about the dangers of radioactive materials are grounded in the story of radium.