Trinity Nuclear Test fallout reached 46 states, Canada and Mexico, study results

In July 1945, as J. Robert Oppenheimer and the other Manhattan Project researchers prepared to test their newest atomic bomb in a New Mexico desert, they knew relatively little about how that megaweapon would perform.

On July 16, when the plutonium implosion device was detonated atop a 100-foot metal tower in a test dubbed “Trinity,” the resulting explosion was much larger than expected. The irradiated mushroom cloud also went many times higher into the atmosphere than expected: 50,000 to 70,000 feet. No one knows where it would have gone in the end.

TO new study, released Thursday before submission to a scientific journal for peer review, it shows that the cloud and its fallout have gone farther than anyone else on the Manhattan Project had imagined in 1945. Using state-of-the-art modeling software and recently discovered historical meteorological data, the study authors say radioactive fallout from the Trinity test reached 46 states, Canada and Mexico within 10 days of the detonation.

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

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

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

“It’s an image frozen in time,” he said.

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

The drift of the Trinity cloud has been monitored by physicists and doctors of the Manhattan Project, but they underestimated its extent.

“They were aware there were radioactive risks, but they were thinking about an acute risk in the areas around the immediate detonation site,” said Alex Wellerstein, a nuclear historian at Stevens Institute of Technology in New Jersey. They had little understanding, he said, of how radioactive materials could become embedded in ecosystems, near and far. “They weren’t really thinking about the effects of low doses on large populations, which is exactly the problem with fallout.”

At the time, Dr. Stafford L. Warren, a Manhattan Project physician specializing in nuclear medicine, reported to Lt. Gen. Leslie Groves, leader of the Manhattan Project, that the Trinity cloud “stood towering over the northeast corner of the site for several hours.” Soon, he added, “we saw various levels moving in different directions.” Dr. Warren assured General Groves that an assessment of the extent of the fallout could be undertaken later on horseback.

In the decades since, a lack of crucial data has plagued evaluations and attempts to study the fallout from the Trinity test. The United States did not have national monitoring stations in 1945 to track fallout, said Dr. Philippe. Furthermore, essential historical meteorological and atmospheric data was only available from 1948 onwards. Remodeling the fallout from the Nevada tests, starting in 1951, was easier, but Trinity remained frustratingly difficult to reanalyze.

“The datasets for the Nevada tests and the available data that we could possibly find for Trinity weren’t comparable,” Ms. Alzner said. “You couldn’t put them on the same map. We decided to keep pushing.”

Determined to fill in the gaps, the team began the study about 18 months ago. Dr. Philippe has extensive experience in fallout modeling and was the author of a similar project in 2021 which documented the effects of French nuclear tests.

A breakthrough came in March when Ms Alzner and Megan Smith, another co-founder of shift7 and a former US chief technology officer in the Obama administration, contacted the National Oceanic and Atmospheric Administration. There, Gilbert P. Compo, a senior research scientist at the University of Colorado and the NOAA Physical Sciences Laboratory, told the team that the European Center for Medium-Range Weather Forecasts just a week earlier had released historical data establishing weather patterns that extended 30,000 feet or more above the Earth’s surface.

“For the first time, we have the most accurate hourly reconstruction of the time up to 1940, worldwide,” said Dr. Compo, who co-authored the study. “Every single event that throws something off, no matter what, can now be tracked, by the hour.”

Using the new data and software created by NOAA, Dr. Philippe then re-analyzed the fallout from Trinity. And while the study authors acknowledge limitations and uncertainties within their calculations, they argue that “our estimates likely remain conservatively low.”

“It’s a very comprehensive and well-executed study,” said MV Ramana, the Simons Professor and Chair in Disarmament, Global and Human Security at the University of British Columbia, who was not involved in the study. Dr. Ramana was not surprised by the findings of the Trinity study. “I expected the old estimates to understate what was actually filed,” he said.

The findings show that New Mexico has been hit hard by the fallout from Trinity. Calculations by Dr. Philippe and his colleagues show the trajectory of the cloud spreading primarily over northeastern New Mexico and a portion of the cloud circling south and west of zero point over the next several days. The researchers wrote that there are “places in New Mexico where radionuclide deposition has reached levels on par with Nevada.”

Trinity’s fallout, Dr. Philippe says, represents 87 percent of the total deposition found throughout New Mexico, which also received deposition from Nevada surface tests. The study also found that Socorro County, where the Trinity test took place, has the fifth-highest deposition per county of all counties in the United States.

Trinity test “downwinders” – a term describing people who lived near nuclear test sites and may have been exposed to lethal radioactive fallout – were never eligible for compensation under the 1990 Radiation Exposure Compensation Act (RECA). It has provided payments of more than $2.5 billion to nuclear workers across much of the western United States and downwinders who were near the Nevada test site and who may have developed cancer or other illnesses from radiation exposure.

“Despite the ongoing Trinity test in New Mexico, many New Mexicans were excluded from the original RECA legislation, and no one has ever been able to explain why,” said Senator Ben Ray Luján, a Democrat from New Mexico. He helped lead congressional efforts to expand and extend the legislation, currently scheduled for sunset in 2024.

The 1940 census data show that up to 500,000 people were live within a 150 mile radius of the test site. Some families lived as far apart as 12 miles, according to the Tularosa Basin Downwinders Consortium. Yet no civilians were warned in advance of the test and were not evacuated before or after the test.

“This new information about the Trinity bomb is monumental and will take a long time,” said Tina Cordova, co-founder of the consortium. “We waited for an affirmation of the stories told by generations of Tularosa people who witnessed the Trinity bomb and talked about how ash fell from the sky for days afterward.”

The study also documents significant deposition in Nevada, Utah, Wyoming, Colorado, Arizona and Idaho, as well as dozens of federally recognized tribal lands, potentially strengthening the case for people seeking expanded compensation in those areas.

Although Dr. Wellerstein said he approaches such historical fallout reanalyses with a certain amount of uncertainty, in part due to the age of the data, he said such studies have value in keeping nuclear history and its legacy in the public discourse.

“The extent to which America has bombed itself is still not fully appreciated, to this day, by most Americans, especially young Americans,” he said.