看LA Times說，日本核電站泄露的第一波放射性汙染物最快將於18日抵達美國加州等西海岸上空，有作準備了嗎？

日本核泄漏物即抵美西：三號反應堆用的是鈈，後果不容樂觀

from: LA Times

美國原子能專家指出，從日本核電站泄露的第一波放射性汙染物最快將於18日抵達美國加州等西海岸上空。不過專家認為，輻射物的含量在安全範圍以內。

據 3月16日報道，日本大地震和海嘯引發核電站泄露事故後，世界各地和美國的檢測網絡密切監視核汙染物的動向。從日本核電站泄露的少量核輻射物正隨高空氣流 飛躍太平洋飄向北美大陸。美國環保部管理的核輻射檢測網絡由100個檢測站組成，該網絡每天24小時不間斷地監控全美各地地核輻射情況，此外還有63個聯 合國“全麵禁止核試驗條約組織”管理的監測站在進行同樣的工作。

美國專家說，來自日本的第一波核汙染物最快將在18日出現在美國西海岸上 空，也有可能晚一周左右抵達。以加州南部的洛杉磯為例，距離日本福島大約有8,000公裏。專家說，2006年朝鮮進行核試驗時，大約兩周後核輻射物到達 美國西海岸上空。

美國原子能管理委員會專家16日表示，抵達美國夏威夷、阿拉斯加、西海岸的核輻射物不會達到危險水平，不過第一波核汙染物 過後，美國上空的核輻射物含量很可能會升高，因為日本核電站核泄漏事故在加劇。該委員會已經要求在日本核電站周邊80公裏範圍內的美國公民迅速撤離。

美 國原子能管理委員會的電腦模擬顯示，在福島第一核電站周圍半英裏範圍內，核輻射水平之高足以致命，即使是80公裏處的輻射劑量也超過每人每年正常接收的輻 射量的16倍。不過專家也指出，即使日本核泄漏物在增加，但輻射物在抵達美國上空時已經被大氣層衝散，濃度會大幅下降。

報道最後提到，一個 不容樂觀的情況是，福島核電站的第三號反應堆使用的是核燃料鈈，這是一種對人類健康極度危險的放射性物質，即使是微小的劑量也會導致嚴重後果。

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Small amounts of radiation headed for California, but no health risk seen

http://www.latimes.com/news/science/la-sci-japan-nuclear-usa-20110317,0,1431467.story

Small amounts of radioactive isotopes from the crippled Japanese nuclear power plant are being blown toward North America high in the atmosphere over the Pacific Ocean and will reach California as soon as Friday, according to experts.

A network of sensors in the U.S. and around the world is watching for the first signs of that fallout, though experts said they were confident that the amount of radiation would be well within safe limits.

Operated by the Environmental Protection Agency, the U.S. network known as Radnet is a system of 100 radiation monitors that work 24 hours a day, spread across the country in places such as Anaheim, Bakersfield and Eureka. In addition, a network of 63 sensors is operated by the Comprehensive Test Ban Treaty Organization, an international agency allied with the United Nations.

Atmospheric experts said the material should begin showing up on the West Coast as early as Friday, though it could take up to an additional week for the 5,000-mile trip from Japan to Southern California. Although the organization has told its member countries that the first indication of radiation would hit on Friday, the plume from a North Korean nuclear test in 2006 took about two weeks to travel to North America, U.N. officials said.

The Nuclear Regulatory Commission, which oversees the U.S. nuclear industry, said Wednesday that it did not expect dangerous levels of radioactivity to hit the West Coast, Hawaii, Alaska or U.S. territories in the Pacific. But whatever levels reach the U.S. initially are likely to increase in subsequent days, because radioactive emissions from the damaged Fukushima Daiichi nuclear power plant have grown since the disaster began Friday. The NRC sharply raised its warning to American citizens in Japan, urging them to evacuate an area within 50 miles of the Fukushima complex. Japanese authorities have ordered an evacuation within about 12 miles of the plant.

The NRC released computerized projections showing that within half a mile of the plant, radiation levels were so high that one could receive a fatal dose, and that even 50 miles away one could receive more than 16 times the average annual dose all people are exposed to from natural sources.

Those numbers were sharply higher than ones the NRC released days earlier. But although the Fukushima reactors are leaking more radiation now, experts continued to say that the particles would wash out of the atmosphere before they could reach the U.S.

So far, Tokyo Electric Power Co., which operates the Fukushima facility, and the Japanese government have not released any measurements or estimates of the total amount of radioactivity released by the accident. These numbers would be crucial to better project whether the material could affect other Asian nations, the Pacific islands or even the U.S.

Edwin Lyman, a specialist at the nuclear watchdog group Union of Concerned Scientists, said that although it was true that the more radioactivity released in Japan the more could migrate away from the region, he did not think the U.S. was at serious risk.

"We can never say never," Lyman said. "My judgment is that there will probably be measurable radiation, but except for a few hot spots it is not something we should really worry about."

Lyman said that the NRC's warning Wednesday to Americans in Japan to evacuate 50 miles from the Fukushima reactors was a long-overdue admission that the agency's prior warnings of a 10-mile exclusion zone from U.S. reactors during an emergency was inadequate.

Key federal officials involved in the Radnet monitoring program have so far not disclosed their predictions for U.S. radioactive exposure. The projections are being developed by the National Atmospheric Release Advisory Center operated at the Lawrence Livermore National Laboratory in Northern California. The center, part of the Energy Department, uses sophisticated models on supercomputers to project the movement of radioactive particles and other toxic substances through the atmosphere.