See photo gallery USS Ronald Regan in Japan

ABOARD THE USS RONALD REAGAN >> When U.S. Navy helicopters returned from a humanitarian mission on the first weekend following Japan’s earthquake and tsunami, Lt. j.g. James Powell felt a slight unease.

Powell, the radiation health officer aboard the USS Ronald Reagan, knew there was a chance the choppers could have been exposed to radiation from the damaged Fukushima Dai-ichi nuclear power plant as they ferried relief aid to northeastern Japan, and even though "the Japanese had told us we’d be fine," he still wanted to be sure.

"I was kind of nervous about it," the 30-year-old nuclear engineer said. "So I said, ‘Let’s just go check them, just in case. … Let’s just go check it out.’"

That was Sunday, March 13 — two days after the earthquake and tsunami had hit the coast and one day after the first explosion from the nuclear plant.

Thus began three days of mostly sleepless nights for Powell as he and others worked to contain contamination to the $4.5 billion nuclear-powered aircraft carrier and calm the nerves of its crew of about 4,500.

Powell’s first examination showed a level of radiation on the nose of a helicopter 50 times higher than the ship’s standard. Further checks showed that helicopter crew members themselves were coming in contaminated.

"I’d never seen it on a nuclear-powered ship before, I’d never seen any skin contamination, never seen any sort of contamination anywhere that it wasn’t supposed to be," Powell said Wednesday in an interview with The Associated Press on the deck of the carrier as sailors cleaned the expansive surface to try to strip it of any residual radioactivity.

While the checks of helicopter crews were being done, air samples were "coming back hot," Powell said of the situation on March 13.

The level of contamination in the air made it difficult to conduct accurate checks on people, so Powell took over the ship’s barber shop — a poorly ventilated space that protected the air inside and kept the contamination level low enough to conduct accurate "frisks," or tests.

Meanwhile, the ship itself was taking evasive action, trying to move out of the area of the radioactive plume. After about two hours, it succeeded, Powell said.

"And then after that, we just started checking out the helicopters, checking out all the people, put them all in this little tiny room," he said. "It was kind of scary."

Powell was quick to point out that contamination levels were never anywhere close to what could be considered dangerous, emphasizing that no one on the ship was exposed to even half the radiation from a chest X-ray. "I would say not even a tenth," he added.

For Powell, the main challenge was all the uncertainty.

"I knew that we were OK as far as what we had hit, but it’s just like, ‘What the hell happened and what’s gonna happen again?’" he said.

Soon the ship’s entire reactor department got involved, setting up a central area, or "brain," with computers to funnel information to a single spot in a conference room, he said.

"We weren’t panicking or freaking out," Powell said of himself and other officers familiar with the effects of radiation. "We were just trying to get a handle on what we had."

The cheery third-generation Navy man from Austin, Texas, studied nuclear engineering and physics at Rensselaer Polytechnic Institute in Troy, New York. His knowledge of radiation and how it works gave him a keen edge over most of the Reagan’s crew members not familiar with the frightening prospect of radioactive contamination.

Keeping a smile on his face was important as he worked to assuage the fears of the crew, who were seeing news reports about contamination that were scaring them and their families back home, he said.

Keeping "the human side" under control was important, Powell said.

Petty Officer 1st Class Kathy Duke of Zuni, New Mexico, said the crew’s lack of experience with such a situation was a source of unease.

"I was a little bit afraid," she said. "I didn’t know — OK, radiation. Nobody’s ever gone through this at all."

Even people who had been in the Navy more than 15 years said they were experiencing this for the first time, Duke said.

At one point, the carrier’s commanding officer announced that there was some radiation in the ship’s drinking water supply, and "I know everybody went down to the vending machines to grab (a) bottle of water," Duke said.

"So I know everybody got a little bit scared," said Duke, who in charge of moving ordnance through the carrier’s hanger bay and sending it up to the flight deck to be loaded onto aircraft.

Cmdr. Ron Rutan, the Reagan’s chief engineer who supervised the swabbing of the deck and other surface areas, said such a cleanup was unprecedented.

"I don’t know of any aircraft carrier that’s ever been contaminated like this," he said.

Powell, the radiation officer, said that he only got two hours of sleep from Sunday until Wednesday. By then, things had calmed down significantly.

That doesn’t mean, however, that the ship has lowered its vigilance. Visitors coming aboard even nine days later were thoroughly checked, as are crews still coming back from relief missions.

The mass cleanup of the ship’s surface Wednesday was considered largely successful, although commanding officer Capt. Thom Burke, in an announcement over the vessel’s public address system the next day, said that some "hot spots" remained.

Powell said he learned some valuable lessons — including how to set up mass decontamination stations — so that things will go smoother in the unlikely event that such an experience happens again.

He also learned something else.

"I know how to deal with 4,500 people freaking out," he said.