An estimated 45,000 people died on the day of the Hiroshima explosion. But during the following months, years and decades, the death toll continued to rise - up to an estimated 166,000.

"Even healthy people, seemingly with no injury, no burns, they looked alright - but they became ill all of a sudden with lots of strange symptoms," Matsushima said. "Like high fever, or bleeding from the gums, or many spots on their bodies. And even doctors did not know how to deal with them. People just named them ‘A-bomb diseases’, that is all.”

During the following decades, these diseases would be recognized as forms of radiation sickness.

New fears

Now the crisis at the Fukushima nuclear power plant, caused by damage from the tsunami, is unleashing a new wave of radiation over parts of Japan.

The government has evacuated everyone from a 20-kilometer radius around the plant. In Tokyo - 250 kilometers to the south - parents have been warned not to give tap water to infants, after it was found to contain high levels of a radioactive element.

The survivors of Hiroshima and Nagasaki - the so-called ‘hibakusha’ - have become the major source of information on the effects of radiation exposure.

Professor Masaharu Hoshi of Hiroshima University has been studying the effects of radiation on atomic bomb survivors ('hibakusha') for 30 years.

Professor Masaharu Hoshi of Hiroshima University has spent three decades studying them. He says his biggest fear now is a sudden surge in radiation levels from the Fukushima plant.