What ills do we risk from radiation to which we are exposed naturally, by choice, or by accident? The question looms large in the aftermath of the meltdown of fuel rods from nuclear reactors at the Fukushima Daiichi power plant in Japan.

Months later, hot spots continue to release radiation as workers at the plant struggle to quench the fuel. Tens of thousands of people have been evacuated and many who remain or who dream of returning worry about their fates.

Radiation released during the Fukushima accident and during the disaster 25 years earlier was detected worldwide. But a detectable amount of radiation does not necessarily pose a risk above background levels. Radiation risks vary with the type, the amount, and the route of exposure.

In this video UCSF physician-scientists and other UC researchers discuss sources of in everyday life, the risks posed by the Fukushima accident and lessons from Chernobyl, and even significant risks from radiation exposure that can arise from some medical imaging exams — CT scanning protocols often used to detect cancer and other serious illnesses.