Trinity (nuclear test)

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Trinity Test Fireball 16ms.jpg
The Trinity explosion, 16 ms after detonation.
CountryUnited States
Test siteTrinity Site, New Mexico
DateJuly 16, 1945
Test typeAtmospheric
Device typePlutonium implosion fission
Yield20 kilotons of TNT (84 TJ)
Previous testnone
Next testOperation Crossroads
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For other uses, see Trinity (disambiguation).
Trinity Test Fireball 16ms.jpg
The Trinity explosion, 16 ms after detonation.
CountryUnited States
Test siteTrinity Site, New Mexico
DateJuly 16, 1945
Test typeAtmospheric
Device typePlutonium implosion fission
Yield20 kilotons of TNT (84 TJ)
Previous testnone
Next testOperation Crossroads
Trinity Site
Trinity Site Obelisk National Historic Landmark.jpg
Trinity Site Obelisk
Trinity (nuclear test) is located in New Mexico
Trinity (nuclear test)
LocationWhite Sands Missile Range
Nearest citySan Antonio, New Mexico
Coordinates33°40′38.28″N 106°28′31.44″W / 33.6773000°N 106.4754000°W / 33.6773000; -106.4754000Coordinates: 33°40′38.28″N 106°28′31.44″W / 33.6773000°N 106.4754000°W / 33.6773000; -106.4754000
Area36,480 acres (147.6 km2)[1]
NRHP Reference #66000493
Significant dates
Added to NRHPOctober 15, 1966[3]
Designated NHLDDecember 21, 1965[4]
Designated NMSRCPDecember 20, 1968[2]

Trinity was the code name of the first detonation of a nuclear weapon, conducted by the United States Army on July 16, 1945, as a result of the Manhattan Project. The new test site, named the White Sands Proving Ground, was built in the Jornada del Muerto desert about 35 miles (56 km) southeast of Socorro, New Mexico, at the Alamogordo Bombing and Gunnery Range (now part of the White Sands Missile Range). It was declared a National Historic Landmark district in 1965, and listed on the National Register of Historic Places the following year.

Trinity used an implosion-design plutonium device, informally nicknamed "The Gadget", of the same design as the Fat Man bomb detonated over Nagasaki, Japan, on August 9, 1945. The complexity of the design required a major effort from the Los Alamos Laboratory, and concerns about whether it would work led to a decision to conduct the first nuclear test. The code name was assigned by Robert Oppenheimer, the director of the Los Alamos Laboratory, after a poem by John Donne.

Fears of a fizzle led to the construction of a steel containment vessel called Jumbo that could contain the plutonium, allowing it to be recovered. In the event, Jumbo was not used. The only structures in the vicinity were the McDonald Ranch House and its ancillary buildings, which scientists used as a laboratory for testing bomb components. A base camp was constructed. By July 1945 there were 250 people working at Trinity, and 425 present on the weekend of the test. Observers included Vannevar Bush, James Chadwick, James Conant, Thomas Farrell, Enrico Fermi, Leslie Groves, Robert Oppenheimer and Richard Tolman.

A rehearsal was held on May 7, 1945 in which 108 tons of high explosive spiked with radioactive isotopes were detonated. The Trinity detonation produced the explosive power of about 20 kilotons of TNT (84 TJ).


Main article: Manhattan Project

The creation of atomic weapons arose out of political and scientific developments of the late 1930s. The rise of fascist governments in Europe, new discoveries about the nature of atoms and the fear of a German nuclear weapon project converged, especially among scientists who were refugees from Nazi Germany and other fascist countries. Most scientists believed that nuclear weapons were not possible, but two refugee scientists at the University of Birmingham, Otto Frisch and Rudolf Peierls, who ironically were conducting nuclear research because their enemy alien status precluded them from working on secret projects, changed this. In what became known as the Frisch–Peierls memorandum, they calculated that just a few kilograms of fissile material would be required – an amount small enough to fit inside an aerial bomb. This spurred the British and United States governments to support an all-out effort.[5]

Practical development began in earnest in June 1942, when these efforts were transferred to the authority of the U.S. Army and became the Manhattan Project.[6] Brigadier General Leslie R. Groves, Jr., became the director of the Project in September 1942.[7] The weapons development portion of this project was located at the Los Alamos Laboratory in northern New Mexico, under the directorship of physicist J. Robert Oppenheimer. Other development work was carried out at the University of Chicago, Columbia University and the Radiation Laboratory at the University of California, Berkeley.[8] Theoretically, enriching uranium was feasible through pre-existing techniques, though it proved difficult to scale to industrial levels and was extremely costly. Production of uranium-235 and plutonium were enormous undertakings given the technology of the 1940s, and accounted for 80% of the total costs of the project. Uranium enrichment was carried out at the Clinton Engineer Works near Oak Ridge, Tennessee, while plutonium production was performed in reactors at the Hanford Engineer Works near Hanford, Washington.[9]

Plutonium is a synthetic element not found in nature in appreciable quantities. The only prior plutonium isolated for the project had been produced in cyclotrons in minute amounts. It turned out that it has relatively complicated physics, chemistry, and metallurgy compared to most other elements.[10] In April 1944, physicist Emilio Segrè at Los Alamos received the first sample of reactor-bred plutonium from the X-10 Graphite Reactor at Oak Ridge, and discovered that it was not as pure as cyclotron-produced plutonium by a significant degree. Specifically, the longer the plutonium remained irradiated inside the reactor—which is necessary for high yields of the metal—the greater the content of the plutonium-240 isotope. This undergoes spontaneous fission at an appreciable rate, and that releases excess neutrons. These extra neutrons implied a high probability that a gun-type bomb with plutonium would detonate too early, before a critical mass was formed, scattering the plutonium and producing a small "fizzle" of a nuclear explosion many times smaller than a full explosion. The practical result was that a simple gun-type Thin Man bomb that the laboratory had been working on would not work.[11]

The impossibility of solving this problem of a gun-type bomb with plutonium was decided upon in a meeting in Los Alamos on July 17, 1944.[12] This forced the Laboratory to turn to an alternative, more practical but more difficult design for a plutonium bomb, an implosion-type atomic-bomb design suggested by mathematician John von Neumann in September 1943. A fissile pit would be surrounded by two different high explosives that produced shock waves of different speeds. By alternating the faster and slower burning explosives in a carefully calculated configuration, they would produce a compressive wave upon their simultaneous detonation. This "explosive lens" effect focused the explosive force inward with enough force to compress the plutonium core to several times its original density. This would rapidly reduce the necessary size of the critical mass of the material, making it supercritical. It would also activate a small neutron source at the center of the core, which would assure that the chain reaction began in earnest. This required a great deal of research work and experimentation in engineering and hydrodynamics before a practical design could be worked out.[13] The entire Los Alamos Laboratory was reorganized in August 1944 to focus on designing a workable implosion bomb.[14]


Map of the Trinity Site


The idea of testing the implosion device was brought up in discussions at Los Alamos in January 1944, and attracted enough support for Oppenheimer to approach Groves. Groves gave approval, but, in view of the immense cost of plutonium and the effort that the Manhattan Project had gone through to make it, on condition that the plutonium could be recovered. The Laboratory's Governing Board then directed Norman Ramsey to investigate how this could be done. Ramsey reported back in February 1944. He proposed that the explosion be limited in size by reducing the number of generations of chain reactions, and that it take place inside a sealed containment vessel, from which the plutonium could be recovered.[15]

However, the means of generating such a controlled reaction were uncertain, and the data obtained would not be as useful as that from a full-scale explosion.[15] Oppenheimer therefore argued that the "implosion gadget must be tested in a range where the energy release is comparable with that contemplated for final use."[16] In March 1944, he obtained Groves's tentative approval for testing a full-scale explosion inside a containment vessel, although Groves worried about how he would explain the loss of a billion dollars worth of plutonium to a Senate Committee in the event of a failure.[15]

Code name[edit]

The exact origin of the code name "Trinity" for the test is unknown, but it is often attributed to Oppenheimer as a reference to the poetry of John Donne. In 1962, Groves wrote to Oppenheimer about the origin of the name, asking if he had chosen it because it was a name common to rivers and peaks in the West and would not attract attention, and elicited this reply:

I did suggest it, but not on that ground... Why I chose the name is not clear, but I know what thoughts were in my mind. There is a poem of John Donne, written just before his death, which I know and love. From it a quotation:

As West and East
In all flatt Maps—and I am one—are one,
So death doth touch the Resurrection. [17]

That still does not make a Trinity, but in another, better known devotional poem Donne opens,

Batter my heart, three person'd God.[18] [19]


Planning for the test was assigned to Kenneth Bainbridge, a professor of physics at Harvard University, working under explosives expert George Kistiakowsky in March 1944. Bainbridge's group was known as the E-9 (Explosives Development) Group. It became the X-2 (Development, Engineering and Tests) Group in the August 1944 reorganisation.[20] Stanley Kershaw, formerly from the National Safety Council, was made responsible for safety.[20] Captain Samuel P. Davalos, the assistant post engineer at Los Alamos, was placed in charge of construction.[21] First lieutenant Harold C. Bush became commander of the Base Camp at Trinity.[22] Scientists William Penney, Victor Weisskopf and Philip Moon were consultants. Eventually seven groups were formed: TR-1 (Services) under John H. Williams; TR-2 (Shock and Blast) under John H. Manley, TR-3 (Measurements) under Robert R. Wilson; TR-4 (Meteorology) under J. M. Hubbard; TR-5 (Spectrographic and Photographic) under Julian E. Mack; TR-6 (Airborne Measurements) under Bernard Waldman; and TR-7 (Medical) under Louis H. Hempelmann.[23]

Test site[edit]

Trinity Site (red arrow) near Carrizozo Malpais

For reasons of safety and security, a remote, isolated and unpopulated area was required. The scientists also wanted a flat area to minimise secondary effects of the blast, and with little wind to spread radioactive fallout. Eight candidate sites were considered: the Tularosa Valley; the Jornada del Muerto Valley; the area Southwest of Cuba, and north of Thoreau; and the lava flats of the El Malpais National Monument, all in New Mexico; the San Luis Valley near the Great Sand Dunes National Monument in Colorado; the Desert training area and San Nicolas Island in Southern California; and the sand bars of Padre Island, Texas.[24]

The sites were surveyed by car and by air by Bainbridge, R. W. Henderson, Major W. A. Stevens and Major Peer de Silva. The site finally chosen, after consult on with Major General, the commander of the Second Air Force on September 7, 1944,[24] was at the northern end of the Alamogordo Bombing Range, in Socorro County between the towns of Carrizozo and San Antonio, in the Jornada del Muerto (33°40′38″N 106°28′31″W / 33.6773°N 106.4754°W / 33.6773; -106.4754).[25]

The only structures in the vicinity were the McDonald Ranch House and its ancillary buildings, about 2 miles (3.2 km) to the southeast. Scientists used this as a laboratory for testing bomb components.[26] Bainbridge and Davalos drew up plans for a base camp with accommodation and facilities for 160 personnel, along with the technical infrastructure to support the test. A construction firm from Lubbock, Texas, was contracted to build the barracks, officers' quarters, mess hall and other basic facilities.[21] The requirements expanded and by July 1945 there were 250 people working at Trinity. On the weekend of the test, there were 425 present.[27]

The Trinity test base camp

Bush's twelve-man military police unit arrived at the site from Los Alamos on December 30, 1944. This unit set up initial security checkpoints around the area, with plans to use horses for patrols. The distances around the site proved too great, so they resorted to using jeeps and trucks for transportation. The horses were used for playing polo.[28][24] Keeping up morale amongst men working long hours under harsh conditions along with dangerous reptiles and insects was a challenge. Bush strove to improve the food and accommodation, and provide organized games and nightly movies.[29]

Throughout 1945, other personnel arrived at Trinity Site to help prepare for the bomb test. As the soldiers at Trinity Site settled in, they became familiar with Socorro County. They tried to use water out of the ranch wells, but found the water so alkaline they could not drink it. They were forced to use U.S. Navy saltwater soap and hauled drinking water in from the firehouse in Socorro. Gasoline and diesel were purchased from the Standard Oil plant there.[28] Military and civilian construction personnel built warehouses, workshops, a magazine and commissary. The railroad siding at Pope, New Mexico, was upgraded by the addition of an unloading platform. Roads were built, and 200 miles (320 km) of telephone wire was strung. Electricity was supplied by portable generators.[30][31]

A hazard of being next to a bombing range was that the base camp was twice bombed in May. When the lead plane on a practice night raid accidentally knocked out the generator or otherwise doused the lights illuminating their target, they went in search of replacement lights, and were not informed of the presence of the Trinity base camp. Damage was done to the stables and the carpentry shop, and a small fire resulted.[32]


Jumbo being brought to the site

Responsibility for the design of a containment vessel for an unsuccessful explosion, known as "Jumbo", was assigned to Robert W. Henderson and Roy W. Carlson of the Los Alamos Laboratory's X-2A Section. The initial calculations were carried out by Hans Bethe, Victor Weisskopf, and Joseph O. Hirschfelder. This was followed by a more detailed analysis by Henderson and Carlson,[22] who drew up a specification for a steel sphere 13 to 15 feet (4.0 to 4.6 m) in diameter weighing 150 tons and capable of handling a pressure of 50,000 pounds per square inch (340,000 kPa). Steel companies were approached about whether they could manufacture it, but they were very uncertain about the prospect of success. After consulting with the railroads, Carlson produced a scaled back cylindrical design. Carlson discovered that a company that normally made boilers for the Navy, Babcock & Wilcox, and made something similar and were willing to give it a try.[33]

As delivered in May 1945,[34] Jumbo was 10 feet (3.0 m) in diameter, 25 feet (7.6 m) long and weighed 214 tons.[35][36] A special train brought it from Barberton, Ohio to the siding at Pope, where it was loaded on a large trailer and towed 25 miles (40 km) across the desert by tractors.[37] At the time, it was the heaviest item ever shipped by rail.[36]

For many of the Los Alamos scientists, Jumbo was "the physical manifestation of the lowest point in the Laboratory's hopes for the success of an implosion bomb."[34] By the time it arrived, plutonium was being manufactured in quantity in the reactors at Hanford, and Oppenheimer was confident that there would be enough for a second test.[33] The use of Jumbo would interfere with the gathering of data on the explosion, the primary objective of the test.[37] A explosion of more than 500 tons of TNT (2,100 GJ) would vaporise the steel and make it hard to measure the thermal effects. Even one of 100 tons of TNT (420 GJ) would send fragments flying, which would be a hazard to personnel and measuring equipment.[38] It was therefore decided not to employ it.[37] Instead, it was hoisted up in a steel tower 800 yards (730 m) from the Gadget, where it could be used for a subsequent test.[33] In the end, Jumbo survived the explosion, although its tower did not.[35]

Other methods of recovering active material in the event of a dud explosion were also considered. One idea was to cover the gadget with a cone of sand. Another was to suspend the Gadget in a tank of water. The CM-10 group at Los Alamos also spent some time studying chemical means for then recovering the active material. As with Jumbo, it was decided not to proceed with these means of containment either.[38]

100-ton test[edit]

Because there would be only one chance to carry out the test correctly, Bainbridge decided that a rehearsal be carried out to allow for the plans and procedures to be verified and the instrumentation to be tested and calibrated. Oppenheimer was initially skeptical, but gave permission, and later agreed that it contributed to the success of the Trinity test.[31]

Men stack crates of high explosives for the 100 ton test

A 20-foot (6.1 m)-high wooden platform was constructed 800 yards (730 m) to the south-east of Trinity ground zero (33°40′16″N 106°28′20″W / 33.67123°N 106.47229°W / 33.67123; -106.47229 and 108 tons of TNT were stacked on top of it. Kistiakowsky assured Bainbridge that the explosives used were not susceptible to shock, and this was proven correct when some boxes fell off the elevator lifting them up to the platform. Flexible tubing was threaded through the pile of boxes of explosives and a radioactive slug from Hanford with 1,000 curies (37 TBq) of beta ray activity and 400 curies (15 TBq) of gamma ray activity was dissolved, and Hempelmann poured it into the tubing.[31][39][40]

The test was scheduled for May 5, but was postponed for two days to allow for more equipment to be installed. Requests for further postponements had to be refused because they would have impacted the schedule for the main test. The detonation time was set for 04:00 MWT (Mountain War Time) on May 7, but there was a 37-minute delay to allow the observation plane to get into position.[41] This was a Boeing B-29 Superfortress from the 216th Army Air Forces Base Unit flown by the Major Clyde "Stan" Shields.[42]

The fireball of the conventional explosion was visible from Alamogordo Army Air Field 60 miles (97 km) away, but there was little shock at the base camp 10 miles (16 km) away.[41] Shields thought that the explosion looked "beautiful", but it was hardly felt at 15,000 feet (4,600 m).[42] Herbert L. Anderson practiced using a converted M-4 Sherman tank lined with lead to approach the 5-foot (1.5 m) deep and 30-foot (9.1 m) wide blast crater, and take a sample of dirt, although the radioactivity was low enough to allow several hours of unprotected exposure. The piezoelectric gauges correctly indicated an explosion of 108 tons of TNT (450 GJ), but Luis Walter Alvarez and Bernard Waldman's were less accurate. An electrical signal of unknown origin caused the explosion to go off 0.25 seconds early, ruining experiments that required split-second timing.[39][43]

The test produced a number of mundane lessons as well. Over 100 vehicles were used for the test. More would be required for the main test, and they would need better roads and repair facilities. More radios were required, and more telephone lines, as the telephone system had become overloaded. Lines needed to be buried to prevent damage by vehicles. A teletype was installed to allow better communication with Los Alamos. A Town Hall was built to allow for large conferences and briefings, and the Mess Hall had to be upgraded. Because dust thrown up by vehicles interfered with some of the instrumentation, some 20 miles (32 km) of road was sealed at a cost of $5,000 a mile.[43][31]


The Gadget[edit]

Norris Bradbury, group leader for bomb assembly, stands next to the partially assembled gadget atop the test tower. Later, he became the director of Los Alamos, after the departure of Oppenheimer.

The term "gadget" was the code name given by the Manhattan Project to the bomb. It gave its name to the Los Alamos Laboratory's weapon physics division, G (for Gadget) Division in August 1944. At the time it did not refer specifically to the one used in the Trinity Test.[44] The Trinity gadget was a Y-1561 device very similar to the Fat Man used a few weeks later in the bombing of Nagasaki, with only minor differences, the most obvious being the absence of the external ballistic casing. The bombs were still under development, and small changes continued to be made to the Fat Man design.[45]

To keep the design as simple as possible, a solid spherical core was chosen rather than a hollow one, although calculations showed that a hollow core would be more efficient. The core's sub-critical mass was compressed to criticality by the implosion. This design became known as a "Christy Core" after physicist Robert F. Christy, who first suggested it in September 1944, and it was provisionally adopted by Oppenheimer and Groves on February 28, 1945.[46]

There are several allotropes of plutonium, but the metallurgists preferred the malleable δ phase. This was stabilised at room temperature by alloying it with gallium. A sphere of plutonium-gallium alloy was formed of two equal hemispheres of plutonium metal plated with silver,[45] designated by serial numbers HS-1 and HS-2.[47] The 6.19 kilograms (13.6 lb) radioactive core generated 15 W of heat, which warmed it up to about 100 to 110 °F (38 to 43 °C),[45] and the silver plating developed blisters that had to be filed down and covered with gold foil; later cores were plated with nickel instead. The Trinity core consisted of just these two hemispheres. Later cores also included a ring with a triangular cross-section to prevent jets forming in the gap between them.[48]

A trial assembly of the Gadget without the active components or explosive lenses was carried out by the bomb assembly team headed by Norris Bradbury at Los Alamos on July 3. It was driven to Trinity and back. A set of explosive lenses arrived on July 7, followed by a second set on July 10. Each was examined by Bradbury and Kistianowsky, and the best ones were selected for use.[49] Final assembly began at the MacDonald Ranch House on July 13. This time the pit was assembled, and the high explosive lenses too. Assembly was completed at 16:45 on July 13. [50]

The Gadget was hoisted to the top of a 100-foot (30 m) steel tower. The height would give a better indication of how the weapon would behave when dropped from a bomber, as detonation in the air would maximize the amount of energy applied directly to the target (as it expanded in a spherical shape) and would generate less nuclear fallout. The tower stood on four legs that went 20 feet (6.1 m) into the ground, with concrete footings. Atop it was an oak platform, and a shack made of corrugated iron that was open on the western side. The Gadget was hauled up with an electric winch.[51] A truckload of mattresses was placed underneath in case the cable broke and the Gadget fell.[50]

The seven man arming party, consisting of Bainbridge, Kistiakowsky, Joseph McKibben and four soldiers including Lieutenant Bush, drove out to the tower to carry out the final arming shortly after 22:00 on July 15.[50]


In the final fortnight before the test, some 250 personnel from Los Alamos were at work at the Trinity site,[52] and Bush's command had ballooned to 125 men guarding and maintaining the base camp. Another 160 men under Major T.O. Palmer were stationed outside the area with vehicles to evacuate the civilian population in the surrounding region should that prove necessary.[53] They had enough vehicles to move 450 people to safety, and had food and supplies to last them for two days. Arrangements were made for Alamogordo Army Air Field to provide accommodation.[54] Groves had warned the Governor of New Mexico, John J. Dempsey, that martial law might have to be declared in the southwestern part of the state.[55]

The 100-foot-tall tower constructed for the test

Shelters were established 10,000 yards (9,100 m) due north, west and south of the tower, known as N-10,000, W-10,000 and S-10,000. Each had its own shelter chief: Robert Wilson at N-10,000, John Manley at W-10,000 and Frank Oppenheimer at S-10,000.[56] Many other observers were around 20 miles (32 km) away, and some others were scattered at different distances, some in more informal situations. Richard Feynman claimed to be the only person to see the explosion without the goggles provided, relying on a truck windshield to screen out harmful ultraviolet wavelengths.[57] Bainbridge asked Groves to keep his VIP list down to just ten. He chose himself, Oppenheimer, Richard Tolman, Vannevar Bush, James Conant, Brigadier General Thomas F. Farrell, Charles Lauritsen, Isidor Isaac Rabi, Sir Geoffrey Taylor and Sir James Chadwick.[53] The VIPs viewed the test from Compania Hill, about 20 miles (32 km) northwest of the tower.[58] The observers set up a betting pool on the results of the test. Edward Teller was the most optimistic, predicting 45 kilotons of TNT (190 TJ).[59] He wore gloves to protect his hands, and sunglasses underneath the welding goggles that the government had supplied everyone with.[58] He also brought suntan lotion, which he shared with the others.[60]

Others were less optimistic. Bethe chose 8,000, Kistiakowsky 1,400, Oppenheimer 300 and Ramsey chose zero – a complete dud.[59] Rabi, the last to arrive, eventually won the pool with a prediction of 18 kilotons of TNT (75 TJ).[61] In addition, Enrico Fermi offered to take wagers among the top physicists and military present on whether the atmosphere would ignite, and if so whether it would destroy just the state, or incinerate the entire planet.[62] This last result had been previously calculated by Bethe to be almost impossible,[63][64] although for a while it had caused some of the scientists some anxiety. Bainbridge was furious with Fermi for scaring the guards who, unlike the physicists, did not have the advantage of their knowledge about the scientific possibilities. His own biggest fear was that nothing would happen, in which case he would have to head back to the tower to investigate.[65]

The explosives of the gadget are raised up to the top of the tower for the final assembly

Julian Mack and Berlyn Brixner were responsible for photography. The photography group employed some fifty different cameras, taking motion and still photographs. Special Fastfax cameras taking 10,000 frames per second would record the minute details of the explosion. Spectrograph cameras would record the wavelengths of light emitted by the explosion, and pinhole cameras to record the gamma rays. A rotating drum spectrograph at the 10,000 yards (9,100 m) station would obtain the spectrum over the first hundredth of a second. Another, slow recording one would track the fireball. Cameras were placed in bunkers only 800 yards (730 m) from the tower, protected by steel and lead glass, and mounted on sleds so they could be towed out by the lead-lined tank.[66] Some observers brought their own cameras despite the security. Segré brought in Jack Aeby's 35mm Perfex 44. It would take the only known well-exposed color photograph of the detonation explosion.[58]


A number of factors went into the choice of date and time. Most were meteorological. The scientists wanted good visibility, low humidity, light winds and low altitude and westerly winds at high altitude. The best weather was predicted between 18 and 21 July. However, the Potsdam Conference was due to start on 16 July and President Harry S. Truman wanted the test to be conducted before the conference began. It was therefore scheduled for 16 July, the earliest date at which the bomb components would be available.[67]

The detonation was initially planned for 04:00 but was postponed because of rain and lightning from early that morning. It was feared that the danger from radiation and fallout would be increased by rain, and lightning had the scientists concerned about accidental detonation.[68] A crucial favorable weather report came in at 04:45,[49] and the final twenty-minute countdown began at 05:10, read by Samuel Allison.[69] By 05:30 the rain had gone.[49] There were some communication problems. The short wave radio frequency for communicating with the B-29s was shared with the Voice of America, and the FM radios shared a frequency with a railroad freight yard in San Antonio, Texas.[65]

Jack Aeby's still photo is the only known well-exposed color photograph of the detonation[58]

At 05:29:21 MWT (plus or minus 2 seconds),[70] the device exploded with an energy equivalent to around 20 kilotons of TNT (84 TJ). The desert sand, which is largely made of silica, melted and became a mildly radioactive light green glass, which was named trinitite.[71] It left a crater in the desert 5 feet (1.5 m) deep and 30 feet (9.1 m) wide.[40] At the time of detonation, the surrounding mountains were illuminated "brighter than daytime" for one to two seconds, and the heat was reported as "being as hot as an oven" at the base camp. The observed colors of the illumination ranged from purple to green and eventually to white. The roar of the shock wave] took 40 seconds to reach the observers. It was felt over 100 miles (160 km) away, and the mushroom cloud reached 7.5 miles (12.1 km) in height.[72] Ralph Carlisle Smith, watching from Compania Hill, wrote:

I was staring straight ahead with my open left eye covered by a welders glass and my right eye remaining open and uncovered. Suddenly, my right eye was blinded by a light which appeared instantaneously all about without any build up of intensity. My left eye could see the ball of fire start up like a tremendous bubble or nob-like mushroom. I dropped the glass from my left eye almost immediately and watched the light climb upward. The light intensity fell rapidly hence did not blind my left eye but it was still amazingly bright. It turned yellow, then red, and then beautiful purple. At first it had a translucent character but shortly turned to a tinted or colored white smoke appearance. The ball of fire seemed to rise in something of toadstool effect. Later the column proceeded as a cylinder of white smoke; it seemed to move ponderously. A hole was punched through the clouds but two fog rings appeared well above the white smoke column. There was a spontaneous cheer from the observers. Dr. von Neumann said "that was at least 5,000 tons and probably a lot more."[73]

In his official report on the test, Farrell wrote:

The lighting effects beggared description. The whole country was lighted by a searing light with the intensity many times that of the midday sun. It was golden, purple, violet, gray, and blue. It lighted every peak, crevasse and ridge of the nearby mountain range with a clarity and beauty that cannot be described but must be seen to be imagined..."[74]

The New York Times journalist William L. Laurence recalled that

A loud cry filled the air. The little groups that hitherto had stood rooted to the earth like desert plants broke into dance, the rhythm of primitive man dancing at one of his fire festivals at the coming of Spring.[75]

After the initial euphoria of witnessing the explosion had passed, Bainbridge told Oppenheimer, "Now we are all sons of bitches."[31] Rabi noticed Oppenheimer's reaction: "I'll never forget his walk;" Rabi recalled, "I'll never forget the way he stepped out of the car ... his walk was like High Noon ... this kind of strut. He had done it."[76]

Film of the Trinity test

Oppenheimer later recalled that, while witnessing the explosion, he thought of a verse from the Hindu holy book, the Bhagavad Gita (XI,12):

If the radiance of a thousand suns were to burst at once into the sky, that would be like the splendor of the mighty one ...[77][78]

Years later he would explain that another verse had also entered his head at that time: namely, the famous verse: "kālo'smi lokakṣayakṛtpravṛddho lokānsamāhartumiha pravṛttaḥ" (XI,32),[79] which he translated as "I am become Death, the destroyer of worlds."[note 1]

In 1965, he was persuaded to quote again for a television broadcast:

We knew the world would not be the same. A few people laughed, a few people cried. Most people were silent. I remembered the line from the Hindu scripture, the Bhagavad Gita; Vishnu is trying to persuade the Prince that he should do his duty and, to impress him, takes on his multi-armed form and says, 'Now I am become Death, the destroyer of worlds.' I suppose we all thought that, one way or another.[80]

John R. Lugo was flying a U.S. Navy transport at 10,000 feet (3,000 m), 30 miles (48 km) east of Albuquerque, en route to the west coast. "My first impression was, like, the sun was coming up in the south. What a ball of fire! It was so bright it lit up the cockpit of the plane." Lugo radioed Albuquerque. He got no explanation for the blast but was told, "Don't fly south."[83]

The results of the test were conveyed to the Secretary of War Henry L. Stimson at the Potsdam Conference in Germany in a coded message from his assistant George L. Harrison:

Operated on this morning. Diagnosis not yet complete but results seem satisfactory and already exceed expectations. Local press release necessary as interest extends great distance. Dr. Groves pleased. He returns tomorrow. I will keep you posted.[84]

The message arrived at the "Little White House" in the Berlin suburb of Babelsberg and was at once taken to Truman and Secretary of State James F. Byrnes.[85]

Harrison sent a follow-up message which arrived on the morning of 18 July:[85]

Doctor has just returned most enthusiastic and confident that the little boy is as husky as his big brother. The light in his

eyes discernible from here to High Hold and I could have heard his screams from here to my farm.[84]

Because Stimson's summer home at High Hold was on Long Island and Harrison's farm near Upperville, Virginia, this indicated that the explosion could be seen 200 miles (320 km) away and heard 50 miles (80 km) away.[86]

Civilian detection[edit]

The bright lights and a huge explosion sparked commotion in New Mexico. Groves therefore had the Second Air Force issue a press release with a cover story that he had been prepared weeks before:

Alamogordo, N.M., July 16

The commanding officer of the Alamogordo Army Air Base made the following statement today: "Several inquiries have been received concerning a heavy explosion which occurred on the Alamogordo Air base reservation this morning. "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 explosives magazine was negligible. "Weather conditions affecting the content of gas shells exploded by the blast may make it desirable for the Army to evacuate temporarily a few civilians from their homes."[87]

The press release was written by Laurence, who was aware of the Manhattan Project. He had prepared four releases for a variety of outcomes,[88] ranging from an account of a successful test (the one which was used) to more catastrophic scenarios involving serious damage to surrounding communities, evacuation of nearby residents, and a placeholder for the names of those killed in the explosion.[89][90] As Laurence was a witness to the test he knew that the last release, if used, might be his own obituary.[88] A newspaper article published the same day stated that "the blast was seen and felt throughout an area extending from El Paso to Silver City, Gallup, Socorro, and Albuquerque."[91] An Associated Press article quoted a blind woman 150 miles (240 km) away who asked "What's that brilliant light?" Such articles appeared in New Mexico, but East coast newspapers ignored them.[88]

Information about the Trinity test was made public shortly after the bombing of Hiroshima. The Smyth Report, released on August 12, 1945, gave some information on the blast, and the edition released by Princeton University Press a few weeks later incorporated the War Department's press release on the test as Appendix 6, and contained the famous pictures of a "bulbous" Trinity fireball.[92] Groves, Oppenheimer and other dignitaries visited the test site in September 1945, wearing white canvas overshoes prevent fallout from sticking to the soles of their shoes.[93]


Major General Leslie Groves and Robert Oppenheimer at the Trinity shot tower remains a few weeks later. The white overshoes were to prevent fallout from sticking to the soles of their shoes.

Film badges used to measure exposure to radioactivity indicated that no observers at N-10,000 had been exposed to more than 0.1 roentgens, but the shelter was evacuated before the radioactive cloud could reach it. The explosion was more efficient than expected and the thermal updraft drew most of the cloud high enough that little fallout fell on the test site. The crater, however, was far more radioactive than expected, and the crews of the two lead-lined Sherman tanks were subjected to considerable exposure. Anderson's dosimeter and film badge recorded 7 to 10 roentgens, and one of the tank drivers, who made three trips, recorded 13 to 15 roentgens.[94]

The heaviest fallout contamination outside the restricted test area was 30 miles (48 km) from the detonation point, on Chupadera mesa where cattle grazed. The fallout here is reported to have settled in a white mist onto a number of the livestock in the area, resulting in local beta burns and a temporary loss of dorsal or back hair. Patches of hair grew back discolored as white fur. The Army bought 75 cattle in all from ranchers; the 17 most significantly marked were kept at Los Alamos, while the rest were shipped to Oak Ridge for long term observation.[95][96][97][98]

Maps of the ground dose rate pattern from the device's fallout at +1 hour,[99] and +12 hours,[100] after detonation are available. Unlike the 100 or so atmospheric nuclear explosions at the Nevada Test Site, conducted later, fallout doses to the local inhabitants have not been reconstructed for the Trinity event, due primarily to scarcity of data.[101]

In August 1945, the Kodak Company observed some spotting/fogging on their film which was, at the time, usually packaged in cardboard containers. Dr. J. H. Webb, a Kodak employee, studied the matter and concluded that the contamination must have come from a nuclear explosion somewhere in the United States. He discounted the possibility that Little Boy was responsible due to the timing of the events. A hot spot of fallout from the Trinity explosion had contaminated the river water that the paper mill in Indiana used to manufacture the cardboard pulp from corn husks.[102] Aware of the gravity of his discovery, Dr. Webb kept this secret until 1949.[103] The physicist's knowledge of the secret project was not altogether surprising considering that the Kodak Company ran the Tennessee Eastman uranium processing plant at Oak Ridge.[104]

This incident, along with the next continental US tests in 1951 set a precedent, and in all subsequent atmospheric nuclear tests at the Nevada test site, United States Atomic Energy Commission officials gave the photographic industry maps and forecasts of potential contamination, as well as expected fallout distributions which enabled them to purchase uncontaminated materials and take other protective measures.[104]

Site today[edit]

In 1952, the site of the explosion was bulldozed, and the remaining trinitite was disposed of. On December 21, 1965 the 51,500-acre (20,800 ha) area Trinity Site was declared a National Historic Landmark district,[1][4] and, on October 15, 1966 was listed on the National Register of Historic Places.[3]

The landmark includes the base camp, where the scientists and support group lived; ground zero, where the bomb was placed for the explosion; and the McDonald ranch house, where the plutonium core to the bomb was assembled. Visitors to a Trinity Site open house are allowed to see the ground zero and ranch house areas. In addition, one of the old instrumentation bunkers is visible beside the road just west of ground zero.[105]

In September 1953, about 650 people attended the first Trinity Site open house. An inner oblong fence was added in 1967, and the corridor barbed wire fence that connects the outer fence to the inner one was completed in 1972. Jumbo was moved to the parking lot in 1979; it is missing its ends from an attempt to destroy it in 1946 using eight 500-pound (230 kg) bombs.[106] The Trinity monument, a rough-sided, lava-rock obelisk about 12 feet (3.7 m) high, marks the explosion's hypocenter.[107]

More than sixty years after the test, residual radiation at the site is about ten times higher than normal background radiation in the area. The amount of radioactive exposure received during a one-hour visit to the site is about half of the total radiation exposure which a U.S. adult receives on an average day from natural and medical sources.[108]

On July 16, 1995, a special tour of the site was conducted to mark the 50th anniversary of the Trinity test, and about 5,000 visitors arrived to commemorate the occasion, the largest crowd for any open house.[109] Since that large crowd, the open houses usually average two to three thousand visitors. The site is still a popular destination for those interested in atomic tourism, though it is only open to the public once a year during the Trinity Site Open House on the first Saturday in April.[110]


  1. ^ Oppenheimer spoke these words in the television documentary The Decision to Drop the Bomb (1965).[80] Oppenheimer read the original text in Sanskrit, and the translation is his own. In the literature, the quote usually appears in the form shatterer of worlds, because this was the form in which it first appeared in print, in Time magazine on November 8, 1948.[81] It later appeared in Robert Jungk's Brighter than a Thousand Suns: A Personal History of the Atomic Scientists (1958),[77] which was based on an interview with Oppenheimer. See Hiya, The Gita of Robert Oppenheimer[82]
  2. ^ The small crater in the southeast corner was from the earlier test explosion of 108 tons of TNT (450 GJ).


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External links[edit]