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Tue Jul 16, 2019, 08:20 AM

74 Years Ago Today; Trinity pierces the pre-dawn sky in New Mexico

https://tinyurl.com/om3cxlj (Wikipedia)

Mushroom cloud seconds after detonation of the Gadget.

Trinity was the code name of the first detonation of a nuclear weapon. It was conducted by the United States Army at 5:29 a.m. on July 16, 1945, as part of the Manhattan Project. The test was conducted in the Jornada del Muerto desert about 35 miles (56 km) southeast of Socorro, New Mexico, on what was then the USAAF Alamogordo Bombing and Gunnery Range, now part of White Sands Missile Range. The only structures originally 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, and there were 425 people present on the weekend of the test.

The code name "Trinity" was assigned by Robert Oppenheimer, the director of the Los Alamos Laboratory, inspired by the poetry of John Donne. The test was of an implosion-design plutonium device, informally nicknamed "The Gadget", of the same design as the Fat Man bomb later 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 test was planned and directed by Kenneth Bainbridge.

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, but Jumbo was not used. A rehearsal was held on May 7, 1945, in which 108 short tons (96 long tons; 98 t) of high explosive spiked with radioactive isotopes were detonated. The Gadget's detonation released the explosive energy of about 22 kilotons of TNT (92 TJ). Observers included Vannevar Bush, James Chadwick, James Conant, Thomas Farrell, Enrico Fermi, Richard Feynman, Leslie Groves, Robert Oppenheimer, Geoffrey Taylor, Richard Tolman and John von Neumann.

The test site was declared a National Historic Landmark district in 1965, and listed on the National Register of Historic Places the following year.


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 he had concerns. The Manhattan Project had spent a great deal of money and effort to produce the plutonium and he wanted to know whether there would be a way to recover it. The Laboratory's Governing Board then directed Norman Ramsey to investigate how this could be done. In February 1944 Ramsey proposed a small-scale test in which the explosion was 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.

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. Oppenheimer argued that the "implosion gadget must be tested in a range where the energy release is comparable with that contemplated for final use." In March 1944, he obtained Groves's tentative approval for testing a full-scale explosion inside a containment vessel, although Groves was still 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.

Code name
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, which in turn references the Christian notion of the Trinity (three-fold nature of God). 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.
That still does not make a Trinity, but in another, better known devotional poem Donne opens,

Batter my heart, three person'd God.



The scientists wanted good visibility, low humidity, light winds at low altitude, and westerly winds at high altitude for the test. The best weather was predicted between July 18 and 21, but the Potsdam Conference was due to start on July 16 and President Harry S. Truman wanted the test to be conducted before the conference began. It was therefore scheduled for July 16, the earliest date at which the bomb components would be available.

The Trinity explosion, 16 ms after detonation. The viewed hemisphere's highest point in this image is about 200 metres (660 ft) high.

The detonation was initially planned for 04:00 MWT 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 a premature detonation. A crucial favorable weather report came in at 04:45, and the final twenty-minute countdown began at 05:10, read by Samuel Allison. By 05:30 the rain had gone. There were some communication problems. The shortwave 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.

Two circling B-29s observed the test, with Shields again flying the lead plane. They carried members of Project Alberta, who would carry out airborne measurements during the atomic missions. These included Captain Deak Parsons, the Associate Director of the Los Alamos Laboratory and the head of Project Alberta; Luis Alvarez, Harold Agnew, Bernard Waldman, Wolfgang Panofsky, and William Penney. The overcast sky obscured their view of the test site.


At 05:29:21 MWT (± 2 seconds), the device exploded with an energy equivalent to around 20 kilotons of TNT (84 TJ). The desert sand, largely made of silica, melted and became a mildly radioactive light green glass, which was named trinitite. It left a crater in the desert 5 feet (1.5 m) deep and 30 feet (9.1 m) wide. 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 changed 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.

Ralph Carlisle Smith, watching from Compania Hill, wrote:

I was staring straight ahead with my open left eye covered by a welder's 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."

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 ...

William L. Laurence of The New York Times had been transferred temporarily to the Manhattan Project at Groves's request in early 1945. Groves had arranged for Laurence to view significant events, including Trinity and the atomic bombing of Japan. Laurence wrote press releases with the help of the Manhattan Project's public relations staff. He later 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.

Original color-exposed photograph by Jack Aeby, July 16, 1945.

After the initial euphoria of witnessing the explosion had passed, Bainbridge told Oppenheimer, "Now we are all sons of bitches." 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."

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

कालोऽस्मि लोकक्षयकृत्प्रवृद्धो लोकान्समाहर्तुमिह प्रवृत्तः। ऋतेऽपि त्वां न भविष्यन्ति सर्वे येऽवस्थिताः प्रत्यनीकेषु योधाः॥११– ३२॥

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 ...

Years later he would explain that another verse had also entered his head at that time:

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.

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."

Ground zero after the test

An aerial photograph of the Trinity crater shortly after the test.


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