Astronauts face radiation threat on long Mars trip

LOS ANGELES (AP) — Astronauts traveling to and from Mars would be bombarded with as much cosmic radiation as they'd get from a full-body CT scan about once a week for a year, researchers reported Thursday.

That dose is enough to raise their cancer risk by about 3 percent, but experts caution that there are many uncertainties about the space environment's effects on the body.

As plans for deep space exploration ramp up, radiation is a big concern — from high-energy galactic cosmic rays spewed by distant supernova explosions to sporadic bursts of charged particles hurled by the sun. Earth's magnetic field helps to deflect much of that harmful radiation.

NASA aims to send a crew to orbit the red planet by the mid-2030s. Private outfits like Inspiration Mars — backed by NASA engineer-turned-space tourist Dennis Tito — are seeking volunteers for a Mars flight.

There have been previous efforts to gauge the radiation risk for future Mars travelers, but the best estimate is coming from NASA's Curiosity mission. Tucked inside the rover when it launched in 2011 was a radiation sensor that took readings during the 8 1/2-month cruise to Mars.

From those figures, scientists calculated a spacefarer's radiation exposure for a quicker six-month voyage in a similarly shielded spacecraft. Roundtrip: about 662 millisieverts. That's a sizable chunk of an astronaut's career cap of 1,000 millisieverts which many international space agencies use to limit the accumulated radiation dosage in space. NASA's threshold varies slightly depending on age and gender.

The dose is similar to getting a full-body CT scan every five or six days, said lead researcher Cary Zeitlin of the Southwest Research Institute in Boulder, Colo.

The estimate is just for zipping there and back; it doesn't include time spent on the Martian surface, which would add to an astronaut's exposure. How much more would depend on length of stay and available shelter.

"You'd like the radiation exposure to be lower, but it is what it is," said Dr. Norm Thagard, the first American to fly on the Russian space station Mir, who had no role in the research. "Given the importance of such a mission, the mission should be done."

The analysis appears in Friday's issue of the journal Science. The amount of radiation likely won't change unless there's a rocket engine that can speed up the interplanetary ride, researchers said.

"You want to get there as quickly as possible" to reduce radiation exposure, said Don Hassler, scientist in charge of the radiation instrument aboard Curiosity.

The radiation dose on a Mars trip would be higher than what crew members cocooned inside the International Space Station typically face — about 200 millisieverts per year. By contrast, people on Earth are typically exposed to about 3 millisieverts a year.

Curiosity flew to Mars during a period of low to moderate solar activity. A manned mission that launches during a solar flare or storm would encounter more radiation. Researchers said astronauts may want to take cover in a safe room aboard the spacecraft when the sun is active, but thicker walls may not keep out energetic cosmic rays and may increase launch costs.

Radiation health experts said there are still many unknowns about deep space travel.

"I think any cancer-related risk estimate at this point would be no more than a rough guesstimate," David Brenner, an expert on radiation-induced cancer at Columbia University, said in an email.

Thagard, the former NASA astronaut, said he was exposed to 120 millisieverts during his 115 days in low-Earth orbit aboard Mir. Despite the potential health risks, Thagard said there likely won't be a shortage of astronauts willing to hop on a Mars flight.

Since landing near the Martian equator last summer, Curiosity has continued to track radiation as it rolls across the dusty surface toward its eventual mountain destination. The rover has turned up the best evidence yet of an ancient watery Mars. A separate study published in Science detailed the existence of more than 500 rounded pebbles near its crater landing site — the result of being shaped by long-ago flowing water.

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Radiation level halts Fukushima cleanup

The new system is supposed to absorb cesium from the highly-contaminated water at the crippled plant.The company had just implements the new cleanup system Friday night The new system is seen as a key part of TEPCO's plan to handle the nuclear crisisIt is supposed to absorb cesium from the water

(CNN) -- Tokyo Electric Power Co. said Saturday that it has temporarily halted the operation of a new cleanup system aimed at cleaning radioactive water in the Fukushima Daiichi nuclear power plant because of higher than expected radiation levels.

The company had just implemented the new cleanup system Friday night, and the system was seen as a key part of TEPCO's plan to handle the nuclear crisis.

The new system is supposed to absorb cesium from the highly-contaminated water.

This apparent setback comes a little more than three months into the crisis at Fukushima Daiichi, the worst nuclear accident since the 1986 Chernobyl disaster.

One of three operating reactors at the plant melted down after the March 11 earthquake and tsunami, and the other two suffered extensive damage to their radioactive cores.

Though no deaths have been attributed to the accident, the resulting contamination has forced authorities to evacuate more than 100,000 people from towns surrounding the plant.

In addition, restrictions on various agricultural and fisheries products have devastated Japanese farmers and fishermen since the disaster began, though some of those bans have been lifted in recent weeks.

CNN

Japan adds to list of radiation hot spots

Katsunobu Sakurai, Minamisoma city mayor of Fukushima prefecture, speaks before the press in Tokyo on Thursday.Three of the four are in the Ryozenmachi areaA fourth spot is in the Haramachi neighborhoodThe four new areas are outside the evacuation zone

Tokyo (CNN) -- Four new areas in northern Japan have been added to the list of places affected by radiation originating from the Fukushima Daiichi nuclear plant, authorities said Friday.

Three of the four are in the Ryozenmachi area, including about 180 households some 50 kilometers (31 miles) from the Fukushima plant, said Takayuki Sato, a Date city official

Government data of the three hot spots showed an estimated radiation level between 20.1 to 20.8 millisieverts per year.

By comparison, the average resident of an industrialized country receives a dose of about 3 millisieverts per year.

The fourth spot is in the Haramachi neighborhood of Minamisoma, 33 kilometers away from the plant but outside of the area where the government has ordered targeted evacuations.

The four new areas are outside the evacuation zone.

Officials have been battling a nuclear crisis at the Fukushima plant following an earthquake and subsequent tsunami on March 11.

CNN

Japan bans green tea on radiation fears

An aerial view of the damaged Fukushima Daiichi nuclear plant.Radioactive cesium levels prompt new action by JapanGreen tea, plums are among the latest bansTokyo Electric hopes to wind down the crisis by January

Tokyo (CNN) -- Japan has slapped new restrictions on green tea and plums from areas around the Fukushima Daiichi nuclear power plant because of lingering radioactive contamination from the ongoing disaster there.

The latest government bans were prompted by the discovery of radioactive cesium-137 and -134 at concentrations higher than Japanese standards allow, Chief Cabinet Secretary Yukio Edano told reporters Thursday.

Both are nuclear waste products: cesium-137 has a half-life of 30 years, while cesium-134 has a two-year half-life.

The government has now forbidden the shipment of both fresh and dried green tea -- normally touted for its health benefits -- from Ibaraki Prefecture, southwest of the plant; from six towns in Chiba Prefecture and six towns in Kanagawa Prefecture, near Tokyo; and two in Fukushima Prefecture, where the crippled plant is located.

In addition, Edano said, the government has banned the shipment of plums from three towns in Fukushima.

The moves come nearly three months into the crisis at Fukushima Daiichi, the worst nuclear accident since the 1986 Chernobyl disaster. One of three operating reactors at the plant melted down after the March 11 earthquake and tsunami, and the other two suffered extensive damage to their radioactive cores.

Though no deaths have been attributed to the accident, the resulting contamination has forced authorities to evacuate more than 100,000 people from towns surrounding the plant. In addition, restrictions on various agricultural and fisheries products have devastated Japanese farmers and fishermen since the disaster began, though some of those bans have been lifted in recent weeks.

The plant's owner, the Tokyo Electric Power Co., has laid out a timetable for restoring normal cooling systems and fully shutting down the reactors by January. But Prime Minister Naoto Kan cautioned that people may not be allowed to return home immediately, "even if these prospects are realized."

"We might have to continue monitoring, and we need to maybe decontaminate," said Kan, whose government survived a no-confidence vote Thursday spurred by complaints about his handling of the twin crises. "And for that, there may be some more time needed."

The disaster has spurred Japan to rethink its commitment to nuclear energy and tighten safety standards for existing plants. A preliminary report from the International Atomic Energy Agency concluded this week that Japan underestimated the risks its nuclear installations faced from tsunamis, like the one that swamped the Fukushima Daiichi plant and knocked out its cooling systems.

But the U.N. nuclear watchdog agency declared the country's response to the disaster "exemplary," praising Tokyo Electric's operators for their "brave and sometimes novel" efforts to contain the crisis.

CNN's Junko Ogura contributed to this report.

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