By Chris Hogg
BBC News, Tokyo
Imagine what it is like to know that as a child you were doused in radioactive fallout.
Keiko Ogura was a young girl when the bomb was dropped
It fell on your clothes and on your skin. It was in the water you drank, the scraps of food you could find. It entered the fabric of the buildings you were sheltering in.
What hidden damage was done in your earliest days?
For those who were in Hiroshima on 6 August 1945 it is a fear they live with constantly.
This is not history for them. It is an everyday concern.
Keiko Ogura was a little girl living in the suburbs of Hiroshima when the bomb was dropped.
"I don't have scars," she says, "but I do have nightmares."
Like thousands of other survivors - the hibakusha, as they are known in Japan - Keiko Ogura was given regular check ups by the Atomic Bomb Casualty Commission in the first few months after the bomb was dropped.
After the war, the Americans provided medical care for those affected. This also enabled scientists to study the effects of radioactive exposure on people.
"Several times the car came and took me to the research centre where they examined me," she said.
"I always had this fear. Is there anything on my body? It was a fear of the invisible. I had a little anaemia, so immediately I asked myself, is that anything to do with the bomb? And then I thought about my future, will I be able to have children normally?"
Keiko Ogura's fears are not unusual. You hear similar stories from others who were exposed to the fallout as children.
The people who were put through the terrible events of August 1945, and their offspring, are more closely monitored than almost anyone else by doctors and scientists.
"This is the only place where we can research the effect of radiation on the human body," said Dr Saeko Fujiwara, at the Radiation Effects Research Foundation.
"We study the relation between the level of exposure and that of radiation. Ours is the only major epidemiological study that can do this. That's why we're unique," she said.
Hiroshima research has helped set safety levels, Charles Waldren says
That study has helped scientists to draw up the guidelines for safe exposure to radiation that is used around the world in the nuclear industry, for example.
Charles Waldren, an American who is the foundation's chief scientist, believes that almost half a million radiation workers in the US and at least that many in Europe have benefited.
"Our research allows people to continue to work at a level of exposure which is considered safe for the general welfare," he said. "I think risk estimates from radiation used in every country in the world come from our data."
But the close monitoring of Hiroshima's citizens, those who were exposed to the blast and their children and grandchildren, is not just a matter of scientific curiosity.
There is real concern about the survivors as they get older. The average age of the hibakushas is 72.
When they were exposed to the radiation, they suffered damage to their genes, with those closest to the centre of the explosion the worst affected.
In many cases their genes repaired themselves. It is possible that those repairs were imperfect, making it more likely that they will develop cancer in later life.
There is an urgency to find new treatments, Kenji Kamiya says
"Radiation induces genome damage," said Professor Kenji Kamiya, the director of the research institute for radiation, biology and medicine at Hiroshima University.
"In some people that isn't fixed correctly. So 60 years later they have problems. The highest risk for A-bomb victims developing cancer is among the youngest who were exposed to the blast. These people are now approaching an age where they would be more likely to develop a cancer anyway," he said.
Science does have some answers, but much more work is needed.
"We are trying to develop new genome technology and new methods for diagnosis and treatment," Professor Kamiya said. "Re-generative medicine offers the possibility of repairing cell damage."
The number of cancer cases among the survivors will continue to rise in the next few years, perhaps peaking in the 2020s.
"That's why we have to rush to develop new treatments for these patients," he said.
Sixty years after the bomb was dropped, science is still working hard to find ways to cope with its after-effects.
And for survivors like Keiko Ogura, that means little chance in the short-term that her anxieties will go away.