So the shot was set for sometime in mid-July, in the heat of the desert summer when the temperature on the Jornada often burned above 100° late in the day. Oppenheimer wired Arthur Compton and Ernest Lawrence: ANY TIME AFTER THE 15TH WOULD BE A GOOD TIME FOR OUR FISHING TRIP. BECAUSE WE ARE NOT CERTAIN OF THE WEATHER WE MAY BE DELAYED SEVERAL DAYS.2379
The senior men arranged a betting pool with a one-dollar entry fee, wagering on the explosive yield. Edward Teller optimistically picked 45,000 tons TNT equivalent. Hans Bethe picked 8,000 tons, Kistiakowsky 1,400. Oppenheimer chose a modest 300 tons. Norman Ramsey took a cynical zero. When I. I. Rabi arrived a few days before the test the only bet left was for 18,000 tons; whether or not he believed that might be the Trinity yield, he bought it.
As of July 9 Kistiakowsky did not yet have enough quality lens castings on hand to assemble a complete charge.2380 Oppenheimer further compounded his troubles by insisting on firing a Chinese copy of the gadget a few days before the Trinity shot to test its high-explosive design at full scale with a nonfissionable core. Each unit would require ninety-six blocks of explosive. Kistiakowsky resorted to heroic measures:
In some desperation, I got hold of a dental drill and, not wishing to ask others to do an untried job, spent most of one night, the week before the Trinity test, drilling holes in some faulty castings so as to reach the air cavities indicated on our x-ray inspection films. That done, I filled the cavities by pouring molten explosive slurry into them, and thus made the castings acceptable. Overnight, enough castings were added to our stores by my labors to make more than two spheres.2381
“You don’t worry about it,” he adds fatalistically.2382 “I mean, if fifty pounds of explosives goes in your lap, you won’t know it.”
Navy Lieutenant Commander Norris E. Bradbury, a brisk, energetic Berkeley physics Ph.D., took charge of assembling the high explosives. On Wednesday, July 11, he met with Kistiakowsky to sort the charges according to their quality. “The castings were personally inspected by Kistiakowsky and Bradbury for chipped corners, cracks, and other imperfections,” writes Bainbridge. “ . . . Only first-quality castings which were not chipped or which could be easily repaired were used for the Trinity assembly. The remainder of the castings were diverted for the Creutz charge”—so named for Edward Creutz, the physicist who was running the Chinese copy test.2383 The castings were waxy, mottled, brown with varnish. They weighed in total, for each device, about 5,000 pounds.
Everyone felt the pressure of the approaching test. It took its toll. “That last week in many ways dragged,” Elsie McMillan remembers; “in many ways it flew on wings.2384 It was hard to behave normally. It was hard not to think. It was hard not to let off steam. We also found it hard not to overindulge in all the natural activities of life.” In a letter to Eleanor Roosevelt in 1950 Oppenheimer recalled an odd group delusion:
Very shortly before the test of the first atomic bomb, people at Los Alamos were naturally in a state of some tension. I remember one morning when almost the whole project was out of doors staring at a bright object in the sky through glasses, binoculars and whatever else they could find; and nearby Kirtland Field reported to us that they had no interceptors which had enabled them to come within range of the object. Our director of personnel was an astronomer and a man of some human wisdom; and he finally came to my office and asked whether we would stop trying to shoot down Venus. I tell this story only to indicate that even a group of scientists is not proof against the errors of suggestion and hysteria.2385
By then the two small plutonium hemispheres had been cast, and plated against corrosion and to absorb alpha particles with nickel, which made the assembly, as metallurgist Cyril Smith would write, “beautiful to gaze upon.”2386 But “an unscheduled change began to be evident three or four days before the scheduled date.” Plating solution trapped beneath the plating on the flat faces of the hemispheres began to blister the nickel, spoiling the fit. “For a time,” says Smith, “postponement of the whole event was threatened.”2387 Completely filing off the blisters would expose the plutonium. The metallurgists salvaged the castings by grinding only partway through the blisters and smoothing the bumpy fit with sheets of gold foil. The core of the first atomic bomb would go to its glory dressed in improvised offerings of nickel and gold.
A tropical air mass moved north over Trinity on July 10, just as the test meteorologist, Caltech-trained Jack M. Hubbard, thirty-nine years old, had predicted. Hubbard had resisted the July 16 date, a Monday, since he first heard of it; he expected bad weather that weekend. The Gulf air suspended salt crystals that diffused a slight haze. On July 12, worrying about Potsdam, Groves confirmed the test for the morning of July 16. Bainbridge passed the word to Hubbard. “Right in the middle of a period of thunderstorms,” the meteorologist stormed to his journal, “what son-of-a-bitch could have done this?” Groves had been awarded such scurrilous genealogy before.2388
The general’s decision started Norris Bradbury and his crews of Special Engineering Detachment GI’s—SED’s, the science-trained recruits were called—assembling the Trinity and Creutz high-explosive charges at two separate canyon sites near Los Alamos mesa that Thursday. They debated filling the small air spaces between the castings with grease. Kistiakowsky decided against such filler, writes Bainbridge, “on the basis that the castings assembled were much better than any previously made and that the air spaces left by the spacer materials were insignificant.”2389 The charges, each of which had been X-rayed one last time and numbered, were papered into snugness instead with facial tissue and Scotch tape. The simplified and improved casing of the unit to be tested, which was designated model 1561, differed from the earlier 1222 casing of bolted pentagons; it featured an equatorial band of five segments machined from dural castings to which were bolted large upper and lower domed polar caps. When the explosives that lined the lower hemisphere had been papered into place Bradbury’s SED’s winched down the heavy tamper sphere of natural uranium, which filled the cavity like the pit in an avocado. The tamper was missing a cylindrical plug; the resulting hole would receive the core assembly. The explosive blocks that formed the upper shell followed next.
For transport to Trinity one set of castings was temporarily left out, replaced by a trapdoor plug through which the core assembly could be positioned in the tamper. The reserved castings—an inner of solid Composition B, an outer lensed—were boxed separately with one spare of each type. The men completed preparing the HE assembly for the slow drive down to Trinity by bagging it in waterproof Butvar plastic, boxing it in a braced shipping crate of knotty pine and lashing the resulting package securely to the bed of a five-ton Army truck. A tarpaulin then muffled its secrets in inconclusive drape.
The plutonium core left the Hill first, at three that Thursday afternoon, shock-mounted in a field carrying case studded with rubber bumpers with a strong wire bail. It rode with Philip Morrison in the backseat of an Army sedan like a distinguished visitor, a carload of armed guards clearing the way ahead and another of pit-assembly specialists bringing up the rear. Morrison also delivered a real and a simulated initiator. At about six o’clock a sunburned young sergeant in a white T-shirt and summer uniform pants carried the plutonium core in its field case into the room at McDonald Ranch where it would spend the night. Guards surrounded the ranchhouse to keep vigil.
For security and to encounter less road traffic the HE assembly would make the trip by night; Kistiakowsky deliberately scheduled that more conspicuous convoy to leave at one minute after midnight on Friday, July 13, to put reverse English on the day’s unlucky reputation. He rode in the lead car with the security guards. He soon dozed off and was then startled awake by the scream of the car’s siren as the convoy ran through Santa Fe; the Army wanted no late-night drunken drivers rolling out of sidestreets to collide with its truckload of handmade high explosives. Beyond Santa Fe the convoy slowed again to below thirty miles an hour; the haul to Trinity took eight hours and Kistiakowsky got some sleep.
On Friday morning at nine the pit-assembly team gathered in white lab coats at McDonald Ranch to begin the final phase of its work. Brigadier General Thomas Farrell was on hand as Groves’ deputy, Robert Bacher as the team’s senior adviser. Bainbridge looked in; so did Oppenheimer. The ranchhouse room where the core had spent the night had been thoroughly vacuumed in preparation and its windows sealed against dust with black electrical tape to convert it to a makeshift clean room. On a table there the assemblers spread crisp brown wrapping paper and laid out the pieces of their puzzle: two gold-faced, nickel-plated hemispheres of plutonium, a shiny beryllium initiator hot with polonium alphas and, to confine these crucial elements, the several pieces of plum-colored natural uranium that formed the cylindrical 80-pound plug of tamper. Before assembly began Bacher asked for a receipt from the Army for the material it would soon explode. Los Alamos was officially an extension of the University of California working for the Army under contract and Bacher wanted to document the university’s release from responsibility for some millions of dollars’ worth of plutonium that would soon be vaporized. Bainbridge thought the ceremony a waste of time but Farrell saw its point and agreed. To relieve the tension Farrell insisted on hefting the hemispheres first to confirm that he was getting good weight. Like polonium but much less intensely, plutonium is an alpha emitter; “when you hold a lump of it in your hand,” says Leona Marshall, “it feels warm, like a live rabbit.”2390 That gave Farrell pause; he set the hemispheres down and signed the receipt.
The parts were few but the men worked carefully. They nested the initiator between the two plutonium hemispheres; they nested the nickel ball in turn in its hollowed plug of tamper. That required the morning and half the afternoon. Two men lugged the heavy boxed assembly on a barrow out to the car. It arrived in its lethal dignity at Zero at 3:18 P.M.
There Norris Bradbury’s crew had been busy with the five-foot sphere of high explosives Kistiakowsky had delivered that morning. At 1 P.M. the truck driver had backed his load under the tower. The men had used a jib winch to lift off the wooden packing crate, had swung it aside and lowered around the sphere a massive set of steel tongs suspended from the main winch anchored one hundred feet up at the top of the tower. With the tongs securing the sphere its two tons were winched up off the truck bed; the driver pulled the truck away and the winch lowered the preassembled unit to a skid set on the asphalt-paved ground. “We were scared to death that we would drop it,” Bradbury recalls, “because we didn’t trust the hoist and it was the only bomb immediately available. It wasn’t that we were afraid of setting it off, but we might damage it in some way.”2391 Before they opened the upper polar cap to expose the trapdoor plug they erected a white tent over the assembly area; thereafter a diffused glow of sunlight illuminated their work.
Inserting the plug courted disaster, team member Boyce McDaniel remembers:
The [high-explosive] shell was incomplete, one of the lenses was missing.2392 It was through this opening that the cylindrical plug containing the plutonium and initiator was to be inserted. . . . In order to maximize the density of the uranium in the total assembly, the clearance between the plug and the spherical shell had been reduced to a few thousandths of an inch. Back at Los Alamos, three sets of these plugs and [tamper spheres] had been made. However, in the haste of last minute production, the various units had not been made interchangeable, so not all of the plugs would fit into all [holes]. Great care had been exercised to make sure, however, that mating pieces had been shipped to [Trinity].
Imagine our consternation when, as we started to assemble the plug in the hole, deep down in the center of the high explosive shell, it would not enter! Dismayed, we halted our efforts in order not to damage the pieces, and stopped to think about it. Could we have made a mistake . . . ?
Bacher saw the cause and calmed them: the plug had warmed and expanded in the hot ranchhouse but the tamper, set deep within the insulation of its shell of high explosives, was still cool from Los Alamos. The men left the two pieces of heavy metal in contact and took a break. When they checked the assembly again the temperatures had equalized. The plug slid smoothly into place.
Then it was the turn of the explosives crew. Oppenheimer watched over them, conspicuous in his pork-pie hat, wasted to 116 pounds by a recent bout of chicken pox and the stress of months of late nights and sevenday weeks. In the motion picture that documents this historic assembly he darts in and out of the frame like a foraging water bird, pecking at the open well of the bomb. Someone hands Bradbury a strip of Scotch tape and his arms disappear into the well to secure a block of explosive. He finished the work in late evening under lights. The detonators were not yet installed. That would be the next day’s challenge after the unit had been hauled to the top of the tower.
The following morning, Saturday, around eight, Bradbury supervised raising the test device to its high platform. The openings into the casing where the detonators would be inserted had been covered and taped to keep out dust; as the bulky sphere rose into the air it revealed itself generously bandaged as if against multiple wounds. It stopped at fifteen feet long enough to allow a crew of GI’s to stack depths of striped ticking-covered Army mattresses up nearly to its skid, a prayer in cotton batting against a damaging fall. Then it started up again, twisting slowly, seeming on its thin, braided steel cable to levitate, rising the full height of the tower and diminishing slightly with distance as it rose. Two sergeants received it into the tower shack through the open floor, replaced the floor panel and lowered the unit onto its skid, positioning it with its north and south polar caps at left and right rather than above and below as they had been positioned during assembly, the same posture in which its militant armored twin, Fat Man, would ride to war in the bomb bay of a B-29. The delicate work of inserting the detonators then began.
Disaster loomed again that day. The Creutz group at Los Alamos had fired the Chinese copy, measured the simultaneity of its implosion by the magnetic method and called Oppenheimer to report the dismaying news that the Trinity bomb was likely to fail. “So of course,” says Kistiakowsky, “I immediately became the chief villain and everybody lectured me.”2393, 2394 Groves flew in to Albuquerque in his official plane with Bush and Conant at noon; they were appalled at the news and added their complaints to Kistiakowsky’s full burden:
Everybody at headquarters became terribly upset and focused on my presumed guilt. Oppenheimer, General Groves, Vannevar Bush—all had much to say about that incompetent wretch who forever after would be known to the world as the cause of the tragic failure of the Manhattan Project. Jim Conant, a close personal friend, had me on the carpet it seemed for hours, coldly quizzing me about the causes of the impending failure.
Sometime later that day Bacher and I were walking in the desert and as I timidly questioned the results of the magnetic test Bob accused me of challenging no less than Maxwell’s equations themselves! At another point Oppenheimer became so emotional that I offered him a month’s salary against ten dollars that our implosion charge would work.
In the midst of this contretemps all of Little Boy but its U235 target pieces slipped away. With two Army officers in escort, a closed black truck and seven carloads of security guards left Los Alamos Saturday morning for Kirtland Air Force Base in Albuquerque. A manifest describes the truck’s expensive cargo:
a. 1 box, wt. about 300 lbs, containing projectile assembly of active material for the gun type bomb.2395
b. 1 box, wt. about 300 lbs, containing special tools and scientific instruments.
c. 1 box, wt. about 10,000 lbs, containing the inert parts for a complete gun type bomb.
Two DC-3’s waiting at Kirtland flew the crates and their officer escorts to Hamilton Field, near San Francisco, from which another security convoy escorted them to Hunter’s Point Naval Shipyard to await the sailing of the U.S.S. Indianapolis, the heavy cruiser that would deliver them to Tinian.
At Trinity gloom was everywhere. A physical chemist from Los Alamos, Josep
h O. Hirschfelder, remembers Oppenheimer’s discomfiture that Saturday evening at the hotel where the guests invited to view the test had begun to assemble: “We drove to the Hilton Hotel in Albuquerque, where Robert Oppenheimer was meeting with a large group of generals, Nobel laureates, and other VIP’s. Robert was very nervous. He told [us] about some experimental results which Ed Creutz had obtained earlier in the day which indicated that the [Trinity] atom bomb would be a dud.”2396
Oppenheimer searched for calm in the midst of this latest evidence of the physical world’s relentlessness and found a breath of it in the Bhagavad-Gita, the seven-hundred-stanza devotional poem interpolated into the great Aryan epic Mahabharata at about the same time that Greece was declining from its golden age. He had discovered the Gita at Harvard; at Berkeley he had learned Sanskrit from the scholar Arthur Ryder to set himself closer to the original text and thereafter a worn pink copy occupied an honored place on the bookshelf closest to his desk. There are meanings enough for a lifetime in the Gita, dramatized as a dialogue between a warrior prince named Arjuna and Krishna, the principal avatar of Vishnu (and Vishnu the third member of the Hindu godhead with Brahma and Shiva—a Trinity again). Vannevar Bush records the particular meaning Oppenheimer clutched that desperate Saturday in July:
His was a profoundly complex character. . . . So my comment will be brief. I simply record a poem, which he translated from the Sanscrit, and which he recited to me two nights before [Trinity]:2397
In battle, in forest, at the precipice in the mountains,
On the dark great sea, in the midst of javelins and arrows,
In sleep, in confusion, in the depths of shame,
The good deeds a man has done before defend him.
Back at Base Camp Oppenheimer slept no more than four hours that night; Farrell heard him stirring restlessly on his bunk in the next room of the quarters they shared, racked with coughing. Chain-smoking as much as meditative poetry drove him through his days.
Making of the Atomic Bomb Page 91
