Trinity (nuclear test)

• 1. Scientific Origins And Design

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  In April 1944, Los Alamos physicist Emilio Segrè made a discovery that threatened to derail the entire Manhattan Project. He found that plutonium produced by the X-10 Graphite Reactor at Clinton Engineer Works contained an impurity called plutonium-240. This isotope undergoes spontaneous fission at thousands of times the rate of pure plutonium-239. The extra neutrons released by this process meant that a gun-type weapon would likely detonate too soon after forming a critical mass. Such an early explosion would produce only a small "fizzle" instead of a full nuclear blast. Project scientists realized the original Thin Man design could not work with this material. They turned to a more technically difficult implosion design. In September 1943, mathematician John von Neumann had proposed surrounding a fissile core with two different high explosives. These explosives produced shock waves of different speeds. Alternating faster and slower burning explosives in a carefully calculated configuration created a compressive wave upon simultaneous detonation. This so-called explosive lens focused the shock waves inward with sufficient force to rapidly compress the solid plutonium core. The increase in density caused the previously subcritical core to become supercritical. At the same time, the shock wave activated a small neutron source at the center of the core. This assured that the chain reaction would begin immediately at the moment of compression. By August 1944, the entire Los Alamos Laboratory reorganized to focus on this complex engineering work.

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• 2. Site Selection And Preparation

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  Safety and security required a remote, isolated, and unpopulated area for the test. Scientists also wanted a flat area to minimize secondary effects of the blast. They needed little wind to spread radioactive fallout. Eight candidate sites were considered across New Mexico, Colorado, California, and Texas. Bainbridge, R. W. Henderson, Major W. A. Stevens, and Major Peer de Silva surveyed these locations by car and air. The site finally chosen on the 7th of September 1944, lay at the northern end of the Alamogordo Bombing Range. It was located in Socorro County near the towns of Carrizozo and San Antonio. The Alamogordo Bombing Range was renamed the White Sands Proving Ground on the 9th of July 1945. Despite the criterion that the site be isolated, nearly half a million people lived within fifty miles of the test site. The only structures in the vicinity were the McDonald Ranch House and its ancillary buildings. These had been acquired by the government in 1942. Scientists used the ranch house as a laboratory for testing bomb components. Bainbridge and Davalos drew up plans for a base camp with accommodation and facilities for 160 personnel. A construction firm from Lubbock, Texas, built the barracks, officers' quarters, mess hall, and other basic facilities. By July 1945, two hundred fifty people worked at the Trinity test site. On the weekend of the test, four hundred twenty-five people were present. Lieutenant Bush's twelve-man MP unit arrived at the site from Los Alamos on the 30th of December 1944. They established initial security checkpoints and horse patrols. The distances around the site proved too great for horses, so they were repurposed for polo playing. MPs resorted to using jeeps and trucks for transportation.

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• 3. The Jumbo Containment Vessel

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  Responsibility for designing a containment vessel fell to Robert W. Henderson and Roy W. Carlson of the Los Alamos Laboratory's X-2A Section. This steel sphere was known as "Jumbo." It weighed one thousand five hundred tons and measured thirty feet in diameter. Hans Bethe, Victor Weisskopf, and Joseph O. Hirschfelder made the initial calculations. They drew up specifications for a steel sphere capable of handling immense pressure. After consulting with steel companies and railroads, Carlson produced a scaled-back cylindrical design. Babcock & Wilcox manufactured the vessel. A special train brought it from Barberton, Ohio, to the siding at Pope. Crews loaded it onto a large trailer and towed it across the desert by crawler tractors. At the time, this was the heaviest item ever shipped by rail. For many scientists, Jumbo represented the lowest point in their hopes for success. By the time it arrived, reactors at Hanford Engineer Works produced plutonium in quantity. Oppenheimer was confident there would be enough for a second test if needed. The use of Jumbo would interfere with gathering data on the explosion. An explosion of more than ten kilotons would vaporize the steel. Even less energy would send fragments flying as hazards. It was decided not to use it. Instead, Jumbo was hoisted up a steel tower three hundred fifty feet from the explosion. In the end, Jumbo survived the explosion, although its tower did not. The rusting skeleton of Jumbo sits in the parking lot at the Trinity site today. It was moved there in 1979.

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• 4. Assembly And Personnel Deployment

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  Assembly of the nuclear capsule began on July 13 at the McDonald Ranch House. The master bedroom had been turned into a clean room. Louis Slotin placed the polonium-beryllium "Urchin" initiator inside the two hemispheres of the plutonium core. Cyril Smith then placed the core in the natural uranium tamper plug. Air gaps were filled with gold foil. Two equal hemispheres of plutonium-gallium alloy were plated with silver and designated by serial numbers HS-1 and HS-2. The radioactive core generated fifteen watts of heat. This warmed it to about thirty degrees Celsius. The silver plating developed blisters that had to be filed down and covered with gold foil. A trial assembly of the bomb without active components was carried out by Norris Bradbury's team on July 3. Explosive lenses arrived on July 7 and again on July 10. Each was examined by Bradbury and Kistiakowsky. Best ones were selected for use. Assembly of active material and high explosives finished at 17:45 hours on July 13. Full assembly of the bomb was completed by 17:00 on July 14. The seven-man arming party drove out to the tower shortly after 22:00 on July 15. In the final two weeks before the test, some two hundred fifty personnel from Los Alamos worked at the site. Lieutenant Bush's command ballooned to one hundred twenty-five men guarding and maintaining the base camp. Another one hundred sixty men under Major T.O. Palmer were stationed outside the area. They had enough vehicles to move four hundred fifty people to safety. Shelters were established due north, west, and south of the tower. Richard Feynman claimed to be the only person to see the explosion without goggles. He relied on a truck windshield to screen out harmful ultraviolet wavelengths.

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• 5. Detonation And Immediate Aftermath

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  The detonation occurred at 5:29:21 MWT (11:29:21 GMT) on the 16th of July 1945. The device exploded with an energy equivalent to approximately twenty-one kilotons of TNT. Desert sand largely made of silica melted and became a mildly radioactive light green glass named trinitite. The explosion created a crater approximately twelve feet deep and three hundred thirty-three feet wide. The radius of the trinitite layer was approximately five hundred feet. The one-hundred-foot tower was completely vaporized. At the time of detonation, surrounding mountains were illuminated brighter than daytime for one to two seconds. Heat was reported as being as hot as an oven at the base camp. Observed colors changed from purple to green and eventually to white. The roar of the shock wave took forty seconds to reach observers. It was felt over ten miles away. The mushroom cloud reached four thousand feet in height. Conant wrote that the enormity of the light stunned him. Lawrence described being enveloped with warm brilliant yellow-white light. Ralph Carlisle Smith watched from Compania Hill and noted the light withdrew into the bomb. Joan Hinton snuck in and said it was like being at the bottom of an ocean of light. She saw a cloud dark and red at the bottom with daylight on top. Thomas Farrell initially exclaimed that the long-hairs had let it get away from them. Bainbridge told Oppenheimer afterward, "Now we are all sons of bitches." Rabi noticed Oppenheimer's walk was like High Noon.

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• 6. Radiation Fallout And Health Impact

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  Film badges used to measure exposure indicated no observers at N-10,000 had been exposed to more than 0.1 roentgens. The shelter was evacuated before the radioactive cloud could reach it. The explosion consumed only eight hundred grams out of six kilograms of plutonium. This left five kilograms to be spread through the atmosphere as fallout. The crater was far more radioactive than expected due to trinitite formation. Crews of two lead-lined Sherman tanks were subjected to considerable exposure. Anderson's dosimeter recorded seven to ten roentgens. One tank driver who made three trips recorded thirteen to fifteen roentgens. Heaviest fallout contamination outside the restricted test area occurred four miles from detonation point on Chupadera Mesa. White mist settled on livestock resulting in local beta burns. Animals suffered temporary loss of dorsal or back hair. Patches of hair grew back discolored white. The Army bought eighty-eight cattle from ranchers. Seventeen most significantly marked animals were kept at Los Alamos. Rest shipped to Oak Ridge for long-term observation. Dose reconstruction published in 2020 documented that five counties experienced greatest radioactive contamination: Guadalupe, Lincoln, San Miguel, Socorro, and Torrance. People living nearby were unaware of project and later not included in 1990 Radiation Exposure Compensation Act support. Efforts in Congress to add New Mexico residents continued in 2024.

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• 7. Legacy And Historic Preservation

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  In September 1953 about six hundred fifty people attended first Trinity Site open house. Visitors allowed to see ground zero and McDonald Ranch House areas. More than seventy years after test residual radiation was about ten times higher than normal background radiation. Amount of radioactive exposure received during one-hour visit is about half total radiation exposure U.S. adult receives on average day from natural and medical sources. On the 21st of December 1965 Trinity Site declared National Historic Landmark district. Listed on National Register of Historic Places the 15th of October 1966. Landmark includes base camp where scientists lived, ground zero where bomb placed, and McDonald ranch house where plutonium core assembled. One old instrumentation bunker visible beside road just west of ground zero. Inner oblong fence added in 1967. Corridor barbed wire fence connecting outer fence to inner one completed in 1972. Trinity monument rough-sided lava-rock obelisk marks explosion hypocenter. Erected in 1965 by Army personnel using local rocks taken from western boundary of range. Special tour the 16th of July 1995 marking fiftieth anniversary attracted five thousand visitors. Since then site open to public first Saturdays April and October.

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