The New York Times reports:

In July 1945, as J. Robert Oppenheimer and the other researchers of the Manhattan Project prepared to test their brand-new atomic bomb in a New Mexico desert, they knew relatively little about how that mega-weapon would behave.

On July 16, when the plutonium-implosion device was set off atop a hundred-foot metal tower in a test code-named “Trinity,” the resultant blast was much stronger than anticipated. The irradiated mushroom cloud also went many times higher into the atmosphere than expected: some 50,000 to 70,000 feet. Where it would ultimately go was anyone’s guess.

A new study, released on Thursday ahead of submission to a scientific journal for peer review, shows that the cloud and its fallout went farther than anyone in the Manhattan Project had imagined in 1945. Using state-of-the-art modeling software and recently uncovered historical weather data, the study’s authors say that radioactive fallout from the Trinity test reached 46 states, Canada and Mexico within 10 days of detonation.

“It’s a huge finding and, at the same time, it shouldn’t surprise anyone,” said the study’s lead author, Sébastien Philippe, a researcher and scientist at Princeton University’s Program on Science and Global Security.

The study also reanalyzed fallout from all 93 aboveground U.S. atomic tests in Nevada and created a map depicting composite deposition of radioactive material across the contiguous U.S. (The team also hopes to study U.S. tests over the Pacific Ocean in the future).

How much of Trinity’s fallout still remain at original deposition sites across the country is difficult to calculate, said Susan Alzner, an author of the study and the co-founder of shift7, an organization that coordinated the study’s research. The study documents deposition as it originally hit the ground in 1945.

“It’s a frozen-in-time image,” she said.

The findings could be cited by advocates aiming to increase the number of people eligible for compensation by the federal government for potential exposure to radiation from atmospheric nuclear explosions.

The drift of the Trinity cloud was monitored by Manhattan Project physicists and doctors, but they underestimated its reach.

“They were aware that there were radioactive hazards, but they were thinking about acute risk in the areas around the immediate detonation site,” Alex Wellerstein, a nuclear historian at the Stevens Institute of Technology in New Jersey, said. They had little understanding, he said, about how the radioactive materials could embed in ecosystems, near and far. “They were not really thinking about effects of low doses on large populations, which is exactly what the fallout problem is.” [Continue reading…]