In July 1945, as J. Robert Oppenheimer and other Manhattan Project researchers prepared to test their new atomic bomb in a New Mexico desert, they knew little about how the mega-weapon would operate.
On July 16, when the plutonium-implosion device was placed atop a hundred-foot metal tower in a test code-named “Trinity,” the resulting explosion was more powerful than expected. The irradiated mushroom cloud also ended up several times higher in the atmosphere than expected: about 50,000 to 70,000 feet. Where it will go is anyone’s guess.
A new study, released Thursday prior to submission to a scientific journal for peer review, shows that the cloud and its fallout were farther away than anyone thought at the Manhattan Project in 1945. Using state-of-the-art modeling software and recently discovered 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 the detonation.
“This is a big 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 analyzed the fallout from all 93 aboveground US atomic tests in Nevada and created a map depicting the cumulative deposition of radioactive material across the contiguous US (The team also hopes to study US tests in the Pacific Ocean in the future).
It’s difficult to calculate how much of Trinity’s effects remain at the original deposition sites across the country, said Susan Alzner, an author of the study and the co-founder of shift7, an organization that coordinated the study’s research. The study records the deposition since it originally hit the ground in 1945.
“It’s a frozen-in-time image,” he said.
The findings could be cited by advocates seeking to increase the number of people eligible for federal government compensation for potential radiation exposure from atmospheric nuclear explosions.
The drift of the Trinity cloud was monitored by physicists and doctors of the Manhattan Project, but they underestimated its reach.
“They know there are radioactive dangers, but they think about the extreme danger in the areas around the immediate explosion site,” said Alex Wellerstein, a nuclear historian at the Stevens Institute of Technology in New Jersey. They have little understanding, he said, of how radioactive materials can embed themselves in ecosystems, both near and far. “They don’t really think about the effects of low doses on large populations, which is exactly what the problem is with the fallout.”
At the time, Dr. Stafford L. Warren, a Manhattan Project physician specializing in nuclear medicine, to Lt. Gen. Leslie Groves, head of the Manhattan Project, said that the Trinity cloud “remained high in the northeast corner of the site for several hours.” Soon, he added, “different levels were seen moving in different directions.” Dr. assured Warren told General Groves that an assessment of the fallout reach could be conducted later on horseback.
In the decades that followed, a lack of valuable data plagued assessments and attempted studies of the Trinity test outcome. The US did not have a national monitoring station in place in 1945 to monitor the fallout, Dr. Philippe. Additionally, important historical weather and atmospheric data are only available from 1948 onwards. The remodeling fallout from the Nevada tests — beginning in 1951 — was easier, but Trinity remained frustratingly difficult to reassess.
“The data sets for the Nevada trials and the available data that we could potentially find for Trinity are not comparable,” Ms. Alzner. “You can’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 an extensive background in fallout modeling and was an author of a similar project in 2021 which documented the effects from French nuclear tests.
A breakthrough came in March, when Ms. Alzner and Megan Smith, another co-founder of shift7 and former chief technology officer of the United States in the Obama administration, at 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 had just a week earlier released historical data that recorded weather patterns reaching 30,000 feet or higher above the Earth’s surface.
“For the first time, we have the most accurate hour-by-hour reconstruction of the 1940 weather, anywhere in the world,” said Dr. Compo, who was a co-author on the study. “Every single event that puts something in the air, whatever it is, can now be tracked, through time.”
Using new data and software developed by NOAA, Dr. Philippe the downfall of the Trinity. And while the study’s authors acknowledge the limitations and uncertainties within their calculations, they maintain that “our estimates are likely to remain conservative.”
“This is a very comprehensive, well-executed study,” said MV Ramana, professor and Simons chair in disarmament, global and human security at the University of British Columbia, who was not involved in the study. Dr. was not surprised. Ramana on the findings of the study about the Trinity. “I expect the old estimates are underestimating what was actually deposited,” he said.
The results show that New Mexico was severely affected by the Trinity collapse. Calculations by Dr. Philippe and his colleagues trace the cloud’s trajectory as it spreads mainly over northeastern New Mexico and a patch of cloud that rotates south and west of ground zero over the next few days. The researchers wrote that there are “locations in New Mexico where radionuclide deposition has reached levels equivalent to Nevada.”
The downfall of Trinity, said Dr. Philippe, accounts for 87 percent of the total deposition found throughout New Mexico, which also received deposition from tests above Nevada. The study also found that Socorro County — where the Trinity trial took place — had the fifth highest per-county deposition 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 deadly radioactive fallout — were never eligible for compensation under the 1990 Radiation Exposure Compensation Act (RECA). It awarded more than $2.5 billion in compensation to nuclear workers in much of the Western US and to downwinders located near the Nevada test site who may have developed cancer or other illnesses as a result of radiation exposure.
“Despite the Trinity test taking place in New Mexico, many New Mexicans were left out of the original RECA law and no one has been able to explain why,” said Senator Ben Ray Luján, a New Mexico Democrat. He helped lead efforts in Congress to expand and extend the law, which is currently due to sunset in 2024.
Census data from 1940 show as many as 500,000 people living within a 150 mile radius of the test site. Some families lived as close as 12 miles away, according to Tularosa Basin Downwinders Consortium. But no civilians were warned about the test in advance, and they were not evacuated before or after the test.
“This new information about the Trinity bomb is huge and has been a long time coming,” said Tina Cordova, a co-founder of the consortium. “We are waiting for an affirmation of the stories told by generations of people from Tularosa who witnessed the Trinity bomb and talked about how ash fell from the sky for days afterward.”
The study also documents significant deposits 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, who approaches such re-evaluations of historical fallout with a certain amount of uncertainty, partly because of the age of the data, says there is value in such studies by keeping nuclear history and its legacy in public discourse.
“The extent of America being nuked is still not fully appreciated, to this day, by most Americans, especially younger Americans,” he said.