In July 1945, as J. Robert Oppenheimer and the other Manhattan Project researchers prepared to test their brand new atomic bomb in a New Mexico desert, they knew relatively little about how that megaweapon would behave.
On July 16, when the plutonium implosion device was launched atop a thirty-foot metal tower in a test codenamed “Trinity,” the resulting blast was much stronger than expected. The irradiated mushroom cloud also entered the atmosphere many times higher than expected: some 50,000 to 70,000 feet. Where it would eventually go was anyone’s guess.
A new study, published Thursday ahead of submission to a scientific journal for peer review, shows that the cloud and its fallout extend farther than anyone in the 1945 Manhattan Project had imagined. Using state-of-the-art modeling software and recently discovered historical weather data, the study authors say 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 Phillippe, a researcher and scientist in Princeton University’s Program on Science and Global Security.
The study also analyzed the fallout from all 93 above-ground US nuclear tests in Nevada and created a map showing the composite deposition of radioactive material in the contiguous US (the team hopes to study US tests over the Pacific in the future as well).
How much of Trinity’s fallout remains at its original deposit 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 deposit as it originally hit the ground in 1945.
“It’s a frozen-in-time picture,” she said.
The findings can be cited by advocates seeking to increase the number of people eligible for compensation from the federal government for potential exposure to radiation from nuclear explosions in the atmosphere.
The drift of the Trinity cloud has been tracked by Manhattan Project physicists and doctors, but they underestimated its reach.
“They were aware that there were radioactive hazards, but they thought of acute risks in the areas around the immediate blast site,” said Alex Wellerstein, a nuclear historian at the Stevens Institute of Technology in New Jersey. They had little understanding, he said, of how the radioactive materials could settle in ecosystems near and far. “They didn’t really think about the effects of low doses on large populations, which is exactly what the fallout problem is.”
At the time, Dr. Stafford L. Warren, a Manhattan Project physician who specializes in nuclear medicine, told Lt. Gen. Leslie Groves, leader of the Manhattan Project, that the Trinity cloud “remained towering over the northeast corner of the site for several hours.” Soon, he added, “different levels were seen in different directions.” Dr. Warren assured General Groves that an assessment of the range of the radioactive fallout could be made later on horseback.
In the decades that followed, a lack of crucial data has made evaluations and attempted studies of the effects of the Trinity test difficult. The U.S. had no national monitoring stations to monitor radioactive fallout in 1945, said Dr. Philippe. In addition, vital historical weather and atmospheric data were not available until 1948. Remodeling the effects of testing in Nevada—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 potentially find for Trinity were not comparable,” Ms. Alzner said. “You couldn’t put them on the same map. We have decided to continue.”
Determined to fill in the gaps, the team began the study about 18 months ago. Dr. Phillippe has extensive background in precipitation modeling and was an author of a similar project in 2021 that documented the effects of French nuclear tests.
A breakthrough came in March when Ms. Alzner and Megan Smith, another shift7 co-founder and former chief technology officer in the United States Obama administration, contacted the National Oceanic and Atmospheric Administration. There, Gilbert P. Compo, a senior researcher at the University of Colorado and the NOAA Physical Sciences Laboratory, told the team that just a week earlier, the European Center for Medium-Range Weather Forecasts released historical data that charted weather patterns extending to 30,000 feet or higher above the Earth’s surface.
“For the first time, we had the most accurate hourly reconstruction of weather up to 1940, around the world,” said Dr. Compo, who became a co-author of the study. “Any event that puts something in the air, whatever it is, can now be tracked down to the hour.”
Using the new data and software built by NOAA, Dr. Phillippe then repercussions from Trinity again. And while the study authors acknowledge limitations and uncertainties in their calculations, they argue that “our estimates are likely to remain conservatively low.”
“It’s a very comprehensive, well-conducted 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. Ramana was not surprised by the study’s findings on Trinity. “I expected the old estimates to be an underestimation of what was actually deposited,” he said.
The results show that New Mexico was badly affected by the Trinity radioactive fallout. From calculations by Dr. Phillippe and colleagues show that the cloud’s trajectory is mostly spreading over northeastern New Mexico, and that part of the cloud will circle 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 comparable to Nevada.”
The fallout from Trinity, says Dr. Phillippe, is responsible for 87 percent of the total deposit in all of New Mexico, which also received deposits from Nevada’s above-ground testing. The study also found that Socorro County – where the Trinity test took place – has the fifth highest deposition by county of any county in the United States.
Trinity test “downwinders” — a term describing people who have lived near nuclear test sites and may have been exposed to deadly radioactive fallout — were never eligible for compensation under the Radiation Exposure Compensation Act (RECA) of 1990. It has provided more than $2.5 billion in payments to nuclear workers across much of the western U.S. and to downwinders who were near the Nevada test site and may have developed cancer or other illnesses as a result of exposure to radiation.
“Despite the Trinity test that took place in New Mexico, many New Mexicans were left out of the original RECA legislation and no one has ever been able to explain why,” said New Mexico Senator Ben Ray Luján, a Democrat. He has helped lead efforts in Congress to expand and expand legislation, which is currently set to expire in 2024.
Census data from 1940 shows that as many as 500,000 people lived within a 150-mile radius of the test site. According to the Tularosa Basin Downwinders Consortium, some families lived as far as 12 miles away. 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 be a long time coming,” said Tina Cordova, co-founder of the consortium. “We’ve been waiting for confirmation of the story told by generations of Tularosa people who witnessed the Trinity bomb and talked about how the ash fell from the sky days later.”
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 extensive compensation in those areas.
Although dr. Wellerstein said he approaches such reanalyses of historical fallout with a degree of uncertainty, in part because of 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 self-bombed is still not fully appreciated by most Americans to this day, especially younger Americans,” he said.
