Trinity test exposed public to radiation and fallout The Online News Source for Los Alamos

Trinity test exposed public to radiation and fallout

ROGER SNODGRASS Monitor Assistant Editor

An important footnote has updated the history of the world’s first test of an atomic bomb at Trinity Site, 62 years ago this week.

The Los Alamos Historical Document Retrieval and Analysis project discussed their findings at a public meeting Wednesday in Pojoaque. Project Director Tom Widner laid out what has now been learned, the public radiation exposure and fallout that resulted from the blast.

While poring through the historical documents at the lab, Widner said, the researchers working under a contract from the Centers for Disease Control found themselves in possession of a great deal of primary information about the development of the implosion weapon that was tested at Trinity.

They studied classified and unclassified documents about the planning for the test, how it was monitored and subsequently investigated. They identified the locations of residents in the area of the site, none of whom had been evacuated or even warned about the test. The researchers added new primary material of their own by interviewing scientists and surviving residents. Pulling all this together with context added from open information sources enabled them to focus on a part of the historic Trinity story that has received relatively less attention.

The story is normally told against the backdrop of World War II, in terms of the race to develop the weapon before the Germans and when that turned out to be unnecessary, to use it to end the war with Japan. The test on July 16, 1945, was related to the beginning of the Potsdam Conference, which began the same day and ended two weeks later with a declaration calling for unconditional surrender of Japan, or “prompt and utter destruction.”

Against this urgent background, secrecy and the safety of the project staff were among the highest priorities, according to an interview with Gen. Leslie Groves, the head of the Manhattan Project charged with mobilizing national resources to deliver the atomic weapon.

Fallout was considered a minor problem, as detailed in the historical summary prepared by LAHDRA, until just weeks before the test. Finally, there were four two-man teams and one five-man team deployed for off-site monitoring. Widner described their equipment as “very crude.”

Although they took soil, air and water samples, those samples have not been found, nor were there any follow up risk assessments about exposure of Trinity workers or the public from the blast.

The team did have equipment for recording radiation exposure in various forms. Many of their measurements were taken on the day after the blast, particularly in a gorge east of the town of Bingham and formerly known as Hoot Owl Canyon, that was later renamed “Hot Canyon” because of its high radioactivity.

Measurements typically reached levels 10,000 times higher than the Nuclear Regulatory Commission currently allows in an unrestricted public area.

“This is not meant to be judgmental,” Widner emphasized. “There were reasons.”

Many local residents, whose locations were largely mapped by intelligence services, were undoubtedly exposed following the blast – from fallout that “snowed down for days” and from residual exposure, particularly from roof-water containers and cattle or goat’s milk that concentrated the radioactivity. The water and milk would have been most likely to be consumed within days afterward, adding to the intensity of those exposures.

There were many gaps in the record, according to the LAHDRA study, including the failure to characterize the residual plutonium, which was not accomplished until three years afterward by a group from the UCLA medical school.

Another gap was the lack of measurements for internal exposure, like nose swabs or bioassay information, which were the main techniques used at the time.

Among lessons learned after the blast was the fact that an explosion conducted near the ground increases the radioactive fallout. Higher elevations became preferred in later tests in the Pacific, because the radioactivity dispersed over a wider area.

An important lesson was that the Trinity site, with a 15-mile radius, was too small. General Groves proposed finding a larger site, “preferably with a radius of at least 150 miles without population,” for any tests in the future.

In response to a question from Ken Silver, a public health advocate who objected to the attention given to the health risks of such a small population, Widner said part of the work of the investigation into the historical records at Los Alamos, was “putting together a story about what happens.”

Not much more effort will be devoted to the Trinity subject, he said, considering the work remaining to be done with the Los Alamos records before the project ends in two years.

The report is available in the “Interim Report of the Los Alamos Historical Document Retrieval and Assessment (LAHDRA) Project” ( in Appendix N.

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