The crisis at the Fukushima Daiichi nuclear power plant following the earthquake and tsunami in Japan has raised many questions about what kind of radiation is leaking and what the health risks of it are. Kenneth Mossman, Professor of Biomedicine and Biotechnology at the University of Arizona, and radiation physicist Jacqueline Yanch, senior lecturer at Massachusetts Institute of Technology, explain radiation—from nuclear fallout, to airport body scanners, to x-rays and medical treatment.