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New Study Reveals Widespread Impact of 1945 Manhattan Project: Fallout Detected Across 46 U.S. States

In July 1945, the Manhattan Project researchers tested their new atomic bomb in a New Mexico desert. The test, code-named “Trinity,” resulted in a blast much stronger than anticipated, with the irradiated mushroom cloud reaching 50,000 to 70,000 feet into the atmosphere.

New Study Reveals Widespread Impact of 1945 Manhattan Project: Fallout Detected Across 46 U.S. States
Photo by Markus Distelrath on

A new study, yet to be peer-reviewed, reveals that the fallout from the Trinity test (Manhattan Project) reached 46 states, Canada, and Mexico within ten days of detonation. This finding is based on state-of-the-art modeling software and recently uncovered historical weather data.

“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 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.

The study’s authors acknowledge limitations and uncertainties within their calculations, but they maintain that “our estimates likely remain conservatively low.”

The results show that New Mexico was heavily affected by Trinity’s fallout (Manhattan Project). Computations by Philippe and his colleagues show the cloud’s trajectory primarily spreading up over northeast New Mexico and a part of the cloud circling to the south and west of ground zero over the next few days. The researchers wrote that there are “locations in New Mexico where radionuclide deposition reached levels on par with Nevada.”

Trinity test “downwinders” — a term describing people who have lived near nuclear test sites and may have been exposed to deadly radioactive fallout — have never been eligible for compensation under the 1990 Radiation Exposure Compensation Act (RECA).

It has provided over $2.5 billion in payments to nuclear workers in much of the Western U.S. and to downwinders who were located near the Nevada test site and may have developed cancer or other diseases as a result of radiation exposure.”

Despite the Trinity test (Manhattan Project) taking place in New Mexico, many New Mexicans were left out of the original RECA legislation and nobody has ever been able to explain why,” said Sen. Ben Ray Luján, D-N.M. He has helped lead efforts in Congress to expand and extend the legislation, due to sunset in 2024.Census data from 1940 shows that as many as 500,000 people were living within a 150-mile radius of the test site. Some families lived as close as 12 miles away, according to the Tularosa Basin Downwinders Consortium.

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