RAY SUAREZ: Sunday will mark a year since the massive earthquake and tsunami struck Japan. The pair of tragic events killed as many as 20,000 people, and led to the partial meltdown of three nuclear reactors at the Fukushima plants.
The Japanese government is expected to be cleaning up radiation for years, and nearly 90,000 residents in an evacuation zone had to leave their homes, likely forever.
NewsHour science correspondent Miles O'Brien recently returned to the area for a series of reports one year later.
Here's the first.
MILES O'BRIEN: Okay. And then the hood up?
MILES O'BRIEN: Near of edge of the Fukushima exclusion zone, the area deemed too hot for human habitation, we geared up for the trip inside.
Tyvek overalls with hoods, booties and masks, coverage from head to toe.
I'm wearing this suit not to protect myself against gamma radiation, but to ensure that any contamination which I pick up while I'm inside the exclusion zone doesn't stay with me when I leave.
We carried a pass that got us through the heavily guarded checkpoint, 20 kilometers, or 12 miles, from the Fukushima Daiichi nuclear power plant. We were traveling with scientists from the University of Tokyo, driving through abandoned cities and towns that once bustled with life, silent now, except for the menacing crescendo of our Geiger counter. It is an eerie post-apocalyptic scene.
At the Manami Elementary School in Naraha, life stood still at 2:46 on the afternoon of March 11, 2011. The blackboards are filled with untaught lessons, book bags left behind, shoes still in the cubbies. The scientists were gathering detailed readings, trying to assess the full extent of the radiation contamination nearly one year after the Fukushima nuclear meltdown.
MILES O'BRIEN: What was it like inside?
WOMAN: It was 0.2 something.
MILES O'BRIEN: Yes, it was 0.5.
The results were mixed. Inside, radiation contamination was relatively low, but out in the playground, too high for kids to play.
"If it's decontaminated, I think the school can open," said scientist Akira Sugiyama.
We visited another school in the city of Namie, a private preschool. There were hot spots, to be sure, but, overall, the readings were relatively low.
I asked the principal, Hitomi Uchimi, whether she wanted to come back.
"To be honest, I have mixed feelings," she told me. "I want to be back and at the same time, I think it's difficult. This area may read low radiation, but the mountains are reading high."
The hydrogen explosions at the nuclear plant a year ago launched radioactive isotopes into the air. They were blown by the wind, then fell with the dew and precipitation. As a result, the footprint of cesium-137, the most prevalent and persistent radioactive fallout, does not match the neat circles of the mandatory and voluntary evacuation zones, 20 and 30 kilometers from the plant.
There are plenty of hot spots outside those circles and some clean spots within, until you get close to the plant.
This is the town of Okuma. We're on Highway 6. We are about a kilometer from the Fukushima Daiichi plant, getting particularly high readings, 34 microsieverts per hour. This is an area where it is hard to imagine they will be remediating and repopulating any time soon.
The readings were 15 times what is considered permissible for radiation workers, 300 times more than the acceptable dose for average citizens. But if that standard were enforced here, it would prompt a dramatically larger evacuation. And that's not going to happen.
So the Japan government has said the standard for radiation workers, 20 millisieverts a year, will apply to everyone for now.
TATSUHIKO KODAMA, University of Tokyo: More than one million residents are living in high radioactivity area now.
MILES O'BRIEN: Tatsuhiko Kodama is a physician, professor and head of the Radioisotope Center at the University of Tokyo. He's also become a YouTube sensation in Japan after this angry testimony before a committee at the parliament.
TATSUHIKO KODAMA (through translator): I am shaking with anger!
MILES O'BRIEN: He believes Tokyo has been slow to respond to the crisis, has withheld information, and has tried to downplay the concern. In fact, the government has been all over the map on what it deems allowable radiation levels for average citizens, at one time saying 33 millisieverts a year would be okay at a school playground.
They were saying higher levels than you would expect for a radiation worker for somebody in kindergarten.
TATSUHIKO KODAMA (through translator): So that was so crazy decision. So, I cannot believe what government is talking about.
MILES O'BRIEN: Given their history, they do not have to look far to get the most accurate scientific data on radiation exposition and its long-term effects on human beings. After all, the atomic age began here.
I went to Hiroshima to learn more about the famous Radiation Effects Research Foundation. Sitting high above a now thriving city, this joint Japan and U.S. project has tracked and studied 94,000 survivors of the Hiroshima and Nagasaki atomic bomb attacks since 1947.
EVAN DOUPLE, Radiation Effects Research Foundation: This is a very exceptionally rare and unique opportunity.
MILES O'BRIEN: Evan Douple is the associate director of research here. He took me on a tour. In liquid nitrogen and 65 deep freezers, scientists here store thousands of blood, urine and other biological samples from bomb survivors and a large control group of their contemporaries who were unexposed.
Is there an aberration here?
MILES O'BRIEN: Researchers analyze stem cells and abnormal chromosomes, looking for signs of damage that can only be explained by exposure to radiation. And they conduct thorough medical exams on a large group of survivors every other year.
They have published now about 1,000 peer-reviewed studies and have found conclusive proof that radiation causes an increase in the rate of leukemia a few years after exposure and, over time, more solid cancers as well.
But below 100 millisieverts, no one here, after all these years, can detect any adverse effects.
EVAN DOUPLE: Extrapolating down, where we tend to have most of our survivors, because radiation is not such a strong mutagen, it becomes more and more difficult to show significance. So, as an epidemiology study, it's a big challenge to try to show effects that are significant at low doses.
MILES O'BRIEN: Scientists are now devising ways to study the people of Fukushima Prefecture, but it will be a challenge to connect the dots. While it is relatively easy to calculate the radiation dose that an atomic bomb survivor received in one instant, determining it for those who receive a very low dose for a very long time is much more of a guessing game.
It's a big job, isn't it?
KAZUO SAKAI, National institute of Radiological Sciences: It is. The target people is more than two million. So -- and that will be a very difficult, very challenging, challenging work.
MILES O'BRIEN: Kazuo Sakai is a radiation biologist with Japan's National Institute of Radiological Sciences. He says a gradual radiation dose is not as harmful as an instantaneous one.
KAZUO SAKAI: When you reduce dose rate, so the effect is becoming smaller and smaller.
MILES O'BRIEN: The body heals, doesn't it?
KAZUO SAKAI: Yes.
MILES O'BRIEN: If you get it all in one shot, it is much more of a shock, right?
KAZUO SAKAI: Yeah, you are right.
MILES O'BRIEN: Right?
KAZUO SAKAI: Yeah.
MILES O'BRIEN: Sakai says six workers at the Fukushima Daiichi plant sustained doses in excess of 250 millisieverts, but none have developed acute radiation sickness.
As for the general population, so far no sign of illnesses. At this hospital in Minamisoma, a city that straddles the 20 kilometer exclusion zone, residents line up all day to be tested for radiation exposure. So far, they have scanned 10,000 people. About half had detectable amounts of cesium-137, but all at levels far below the threshold for concern.
"It was unfortunate that people were exposed to radiation, but the radiation level is very low," says the hospital director, Yukio Kanazawa. "That's our conclusion."
At the conclusion of my journey into the hot zone, I too got a thorough check -- fortunately, no cause for concern.
Did I pass? No problem?
MAN: No problem.
MILES O'BRIEN: It was the end of a sad visit. There may be no proof that living with low levels of radiation contamination can make you sick, but the absence of evidence is not enough to wipe away the evidence of absence. And the emboldened wild boar will likely have free rein here for decades to come.