Just about the time we crossed into the no-entry zone surrounding the Fukushima Daiichi nuclear plant, the dosimeter clipped to our car window introduced its soundtrack: Chirp-chirp. Chirp-chirp. Chirp-chirp.

A feral ostrich, which is believed to run away near a ostrich farm, is seen at the Tomioka fishing port , no-entry zone near the crippled Fukushima No. 1 nuclear power plant. (Eiji Kaji/Ymiuri)

The dosimeter was blue, about the size of a pager, and it updated its readings of the airborne radiation levels every 30 seconds. Any reading over 2.50 microsieverts (uSv) per hour triggered the chirp. It was 9:30 a.m. when we entered the no-go zone, flashing a permit to five policemen at a checkpoint, and for the next six hours, the chirping never stopped.

Since the March 11 natural disaster triggered a nuclear crisis, many Japanese have turned into self-taught experts on radiation dangers. They’ve learned about cesium and microsieverts and half-lifes. But even after they’ve mastered the glossary, they discover a more troubling roadblock: When it comes to non-acute exposure, we still don’t really know what levels cause danger. Research conflicts. And most people in Japan, as a fallback, have resorted to the government’s guidelines.

Which are:

* No nuclear plant worker should receive more than 250,000 uSv per year.

* No adult should receive more than 20,000 uSv per year.

Do the math in reverse, dividing 20,000 uSv by 365 days and 24 hours, and you come up with the hourly radiation level that puts you on target for the ordinary-adult limit: 2.28 uSv per hour. The number is arbitrary, of course — who spends his or her life in one spot? — but it also has practical applications, particularly in Fukushima. If your front yard gives off radiation levels of 2.28 uSv/hr, you might want to think about moving.

As we drove deeper into the no-entry zone, curving past beautiful and empty homes with tile roofs, the numbers on our dosimeter started to soar well beyond the safe-guideline level.

3.41 uSv/hr.

7.12 uSv/hr.

12.03 uSv/hr.

32.04 uSv/hr.


Our guide, a local rancher with a permit for the area, stopped his Isuzu SUV. We were about eight or nine miles from the nuclear plant, I’d guess, with thick trees on both sides. The rancher, Masami Yoshizawa, placed the dosimeter on the ground. We waited for new numbers to flash.

71.32 uSv/hr.

That’s 2.5 times the level at the front gate of the nuclear plant.

Stand in that spot for a year, and you’d be exposed to almost 625,000 uSv--36 times the annual maximum.

We gawked at the dosimeter - or at least the two Washington Post reporters did. Yoshizawa told a five-minute story about cattle ranchers, and only once he stopped did we return to his car.

Yoshizawa makes daily trips into this no-entry zone, tending to the contaminated cattle that the government wants him to euthanize. Taking care of the animals has become his mission, and he’s willing to take a health risk. Plus, he’s 57, and his boss, Jun Murata, acknowledged that the ranchers’ lifestyle was less than healthy.

View Photo Gallery: Beyond the crippled Fukushima Daiichi nuclear plant, for at least 12 miles in any direction, the Japanese government maintains a no-entry zone.

“We smoke and drink all the time,’’ Murata said. “Even if we would develop cancer, we wouldn’t know whether it came from radiation or smoking too much.”

Yoshizawa had his body tested for radiation in July, and a doctor told him his levels were on the “high end.” But Yoshizawa didn’t change his daily routine.

But each person calculates his own risks differently. For me, I balanced the desire to write a story from an eerie and important place against the desire to keep my mother worry-free. Yoshizawa, for this trip, also gave me a second radiation measuring tool, like an odometer, that measures cumulative radiation levels. We set it to zero when entering the no-go zone. Six hours later, it said I’d been exposed to just 20 uSv. I wore no mask and no special protective material.

Even within the sealed off 12-mile area around the plant, radiation levels are fickle. In the early afternoon we headed closer to the plant - but levels went down. At one point we were just three miles from the nuclear plant, but hourly readings were roughly 3 uSv.

Monitoring data from Japan’s science ministry paints a similar picture. The data comes from 51 monitoring areas sprinkled within the no-entry zone. One spot four miles from the plant is on pace to get 116,800 microsieverts this year. Another spot five miles from the plant is on pace to get 3,900.

At no point during my time inside the no-go zone did I feel unsafe. But admittedly, that’s more a result of mindset than fact. Still, just to be safe, when I returned to my apartment in Tokyo, I took off my sneakers, dropped them into a plastic bag, and tossed them into a dumpster.

Three days later, I took a 12-hour flight from Tokyo to Washington, D.C, for the start of a vacation.

Because air travel brings with it a dose of cosmic radiation, I was exposed to roughly 100 microsieverts — five times my total exposure in the no-entry zone.

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