Fallout from the Trinity nuclear test

Fallout from the Trinity nuclear test in 1945 impacted a broad swath of eastern New Mexico with hundreds of thousands of people exposed to radioactivity. The most-at-risk counties had a population of about 65,000. The priority of the US government was to develop a bomb that could be used to end World War II. The scientists and the military conducting the test had limited insight and paid little attention to the impact of radioactive fallout on the health of local residents. Radioactive fallout was heaviest 20 miles (32 km) to the northeast of the bomb test and in one location at that distance fallout was measured at levels likely to cause serious illness. Not many locations were monitored.

According to studies undertaken decades after the bomb test, cancers attributable to fallout probably numbered several hundred. Anecdotal evidence cites many deaths, especially a high incidence of death among infants born shortly after the test. Compensation by the US to people impacted by later nuclear tests in Nevada did not include New Mexicans impacted by the Trinity nuclear test.

The Trinity nuclear test took place on the morning of July 16, 1945 on what is now the White Sands Missile Range in New Mexico. The bomb was detonated on top of a 100 ft (30 m) tower. The bomb contained 13 lb (5.9 kg) of plutonium, but only about three pounds was necessary to create a critical mass of fissionable material for a bomb. The remaining 10 pounds of plutonium was dispersed in the fireball and cloud that followed the blast and climbed to an altitude of an estimated 60,000 ft (18,000 m) into the atmosphere, much higher than the scientists predicted. The explosion also swept up into the fireball hundreds of tons of dirt from below the tower which became highly radioactive. The distribution far and wide of the excess plutonium plus the radioactive dirt gave the Trinity test the characteristics of what would later be called a dirty bomb.

The test was conducted with a maximum of secrecy, but the fireball and the emblematic mushroom cloud were seen as far away as 160 miles (260 km) in Albuquerque and El Paso. The radioactive cloud broke into three parts. One part drifted east, a second west and northwest, and the third and largest to the northeast where it covered an area 100 miles (160 km) long and 30 miles (48 km) wide. The cloud from the blast was visible to near Vaughn, 96 miles (154 km) from the Trinity site.

A cover story distributed to newspapers explained what was seen by New Mexicans after the blast. "A remotely located ammunition magazine containing a considerable amount of high explosives and pyrotechnics exploded. There was no loss of life or injury to anyone, and the property damage outside of the explosive magazine itself was negligible. Weather conditions affecting the content of the gas shells exploded by the blast may make it desirable for the Army to temporarily evacuate a few citizens from their homes."

Army officer Leslie Groves led the Manhattan Project to build the bomb. He and a sizeable contingent of scientists and military personnel observed the blast from bunkers constructed 10,000 yd (9,100 m) from the blast site. J. Robert Oppenheimer headed the scientists. They had little insight as to what would happen when the bomb was detonated. Their speculations of what the bomb would yield in its explosion varied from 300 to 45,000 tons of TNT. (In 2021, the yield of the Trinity bomb was calculated to have been 24,800 tons of TNT.) The initial euphoria of the scientists that their work had succeeded faded quickly as they became aware that "something very grave and strong had happened..." In a seminar five days later British mathematician William Penny emphasized the gravity saying that "this [weapon] would reduce a city of three or four hundred thousand people to nothing but a sink for disaster relief, bandages, and hospitals."

The scientists thought that the dangers to the public from the Trinity test "were modest given the proper weather." However, the weather (which was not ideal) became secondary to the desire of President Harry Truman to inform allies of the bomb at the Potsdam Conference, which convened on July 16.

Scientists were aware of the risk of radioactive fallout. Five years before the bomb blast, physicists Otto Frisch and Rudolf Peierls said, "Owing to the spread of radioactive substances with the wind, the bomb could probably not be used without killing large numbers of civilians...[I]t would be very important to have an organization which determines the exact extent of the danger area, by means of ionization measurements, so that people can be warned from entering it." In June 1945, two physicists warned that "radiation effects might cause considerable damage in addition to the blast damage ordinarily considered." One of the scientists, Joseph O. Hirschfelder later said, "very few people believed us when we predicted radioactive fallout from the atom bomb." Less than a month before the Trinity test, Stafford Warren, chief of the medical section of the Manhattan Project, persuaded Groves to assemble a team to track radioactive fallout, "a hasty effort motivated primarily by concern over legal liability." A critic later said that "the spectre of lawsuits haunted the military, and most of the authorities simply wanted to put the whole test and its aftermath out of sight and mind."