A Tokyo Electric Power Co. (TEPCO) employee, wearing a protective suit and a mask, walks in front of the No. 1 reactor building at TEPCO’s Fukushima Daiichi nuclear power plant.
Credit: Toru Hanai/Bloomberg

Some of the radioactive material that escaped the Fukushima Daiichi nuclear reactor in 2011 took a form no one was looking for, scientists have discovered. Now they have to figure out what it means for Japan and for future disasters.

Radioactive cesium—specifically, cesium-137—is one of the waste products of nuclear power. It’s also one of the most dangerous substances in a nuclear disaster like Chernobyl or Fukushima.

One reason why is that the type of radiation it emits is particularly damaging to our bodies. Another is that cesium-137 dissolves in water. That means it can spread quickly through the environment and get into the plants, animal and water we […]