Cows that consume feed, grass or water contaminated with radioactive iodine-131 can concentrate the element in their milk. Peter Elvidge/ hide caption

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Mike Barlow has been installing geothermal systems for 20 years. But he says a 30 percent federal tax credit is increasing the popularity of the systems for families with modest houses. Elizabeth Shogren/NPR hide caption

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Tokyo Electric Power Co. Chairman Tsunehisa Katsumata (second from right) and other executives bow prior to a press conference at the company's headquarters in Tokyo on Wednesday. Kazuhiro Nogi/AFP/Getty Images hide caption

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In 1992, 28,800 rubber ducks were lost at sea. What happened to them is the subject of Donovan Hohn's book Moby-Duck. Jose Gil/ hide caption

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Cooling towers from the Limerick Generating Station, a nuclear power plant in Pottstown, Pa., sit near a neighborhood. Environmentalists agree that in light of Japan's nuclear crisis, the U.S. should examine existing nuclear plants for safety risks. Stan Honda/AFP/Getty Images hide caption

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Japan Self-Defence Force officers in radiation protection suits hold a blue sheet over workers who were exposed this week to high levels of radiation at the Fukushima Dai-ichi plant. Jiji Press/AFP/Getty Images hide caption

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Nighthawks are known for their repeated "peent" call as they hunt for flying insects. Bill Bouton/Flickr hide caption

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This computer model shows how a plume of radioactive iodine-131 could spread in the atmosphere. ZAMG hide caption

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Japanese Buddhist monk Tanaka Tokuun, who was evacuated from Fukushima prefecture, looks over an instrument measuring radiation levels at a hotel on March 17. Buddhika Weerasinghe/Getty Images hide caption

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Keiji Nagashima has been farming spinach in Ibaraki prefecture for 25 years but will be destroying this year's crop because of fears of radiation exposure. "I can't have a life without the spinach," he says. Richard Harris/NPR hide caption

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