sharing 4.03 MeV. The positively charged proton dumped more energy into the deuterium mass. The tritium nucleus fused in turn with another deuterium nucleus to form an alpha particle and a high-energy neutron that shared 17.59 MeV. The 14-MeV neutrons from this reaction began to escape the hot, compressed deuterium plasma and encountered the U238 nuclei of the vaporized uranium pusher. U238 fissions when it captures neutrons with energies above 1 MeV; so the U238 of the uranium pusher began to fission then under the intense neutron bombardment, flooding more X rays back into the deuterium mass from the outside just as the sparkplug fission reaction was radiating them from the inside, trapping the deuterium between two violent walls of heat and pressure. Deuterium-bred tritium fused with tritium as well, producing a helium nucleus and two neutrons that shared 11.27 MeV of energy. At lower orders of probability, deuterium captured a neutron and bred tritium; deuterium-bred helium fused with deuterium and made heavy helium plus a highly energetic proton, or captured a neutron and bred tritium plus a proton. All these reactions contributed to the force of the Mike explosion.
D + D > 3He + n + 3.27 MeV (1)
D + D > T + p + 4.03 MeV (2)
D + T > 4He + n + 17.59 MeV (3)
T + T > 4He + n + n+ 11.27 MeV (4)
6Li + n > 4He + T + 4.78 MeV (5)
3He + D > 4He + p + 18.35 MeV (6)
D = 2H (deuterium); T = 3H (tritium)
Moving outward from the cauldron of the secondary as gamma and X-radiation and as escaping high-energy neutrons, that explosion swelled back across the path the radiation-driven implosion had taken. Just as the big uranium pusher had served as a tamper for the secondary, so the thick, lead-lined Mike casing served as a tamper for the entire complex explosion, holding it together a few microseconds longer to give the fuel more time to react, but massive as the casing was, bomblight from its outer surface revealed the breakthrough of the developing explosion before the mass had time even to swell, much less to move.
Once the explosion broke through the casing, it expanded in seconds to a blinding white fireball more than three miles across (the Hiroshima fireball had measured little more than one-tenth of a mile) and rose over the horizon like a dark sun; the crews of the task force, thirty miles away, felt a swell of heat as if someone had opened a hot oven, heat that persisted long enough to seem menacing. “You would swear that the whole world was on fire,” one sailor wrote home who turned around like Lot's wife to look. For a moment the fireball seemed to hover; then it began to rise. Los Alamos radiochemist George Cowan, a precise man whose ingenious tests would help measure Mike's yield, was there that day:
I was stunned. I mean, it was big. I'd been trying to visualize what it was going to be like, and I'd worked out a way to calibrate the shot. The initial fireball I guess I calibrated by holding up a quarter. If the quarter would cover the fireball then the yield would be less than something; if the fireball were bigger than the quarter, then it would be more than something. The question was, looking through my dark glasses, could I cover the fireball with a quarter. And I couldn't, so I knew it was big. As soon as I dared, I whipped off my dark glasses and the thing was enormous, bigger than I'd ever imagined it would be. It looked as though it blotted out the whole horizon, and I was standing on the deck of the
Momentarily, the huge Mike fireball created every element that the universe had ever assembled and bred artificial elements as well. “In nanoseconds,” writes the physicist Philip Morrison, “uranium nuclei captured neutron upon neutron to form isotopes in measurable amounts all the way from 239U up to mass number 255. Those quickly decayed, to produce a swath of transuranic species from uranium up to element 100, first isolated from that bomb debris and named fermium.”
Swirling and boiling, glowing purplish with gamma-ionized light, the expanding fireball began to rise, becoming a burning mushroom cloud balanced on a wide, dirty stem with a curtain of water around its base that slowly fell back into the sea. The wings of the B-36 orbiting fifteen miles from ground zero at forty thousand feet heated ninety-three degrees almost instandy. In a minute and a half, the enlarging fireball cloud reached 57,000 feet; in two and a half minutes, when the shock wave arrived at the
Down below, Elugelab had vanished. The fireball had vaporized the entire island, leaving behind a circular crater two hundred feet deep and more than a mile across filled with seawater, a dark blue hole punched into the paler blue of the shallow atoll lagoon. The explosion vaporized and lifted into the air some eighty million tons of solid material that would fall out around the world. It obliterated the Krause-Ogle box and burned and damaged the Bogon bunker. It stripped animals and vegetation from the surrounding islands and flashed birds to cinders in midair. A survey team afterward discovered general ruin:
Rigili is fourteen miles south-southwestward down the lagoon from the Mike shot crater. Yet there the survey team found that the trees and brush facing the test site had been scorched and wilted by the thermonuclear heat. Many of the terns there were sick, some grounded and reluctant to fly and some with singed feathers, particularly the noddy terns and the sooty terns, whose feathers are dark in color…
At Engebi [three miles from ground zero] the group went ashore on an island where the sense of desolation was deepened by the presence of a reinforced concrete building, ruptured and shaken but still standing, on the island flat that had been swept by the blast and the succeeding surge of water. The body of a bird was seen, but no living animals and only the stumps of vegetation… Among the specimens collected were fish which seemed to have been burned. On each of these fish, the skin was missing from one side, as if, the field notes said at the time, the animal “had been dropped in[to] a hot pan.”
Red Leader, an F-84 sampler aircraft piloted by a colonel named Meroney, flew into the stem of the mushroom cloud at 42,000 feet almost two hours after the explosion,
Immediately upon entering the cloud, Red Leader was struck with its intense color. It cast a red glow over the cockpit and his radiological instruments indicated maximum readings… The hand on the Integron, which showed the rate at which radioactivity was being accumulated, “went around like the sweep second hand on a watch… And I had thought it would barely move!” The combination of most instruments indicating maximum readings and the red glow like the inside of a red-hot furnace was “staggering” and Colonel Meroney quickly made a ninety-degree turn to leave the cloud.
Fireball measurements and subsequent radiochemistry put the Mike yield at 10.4 megatons — the first megaton-yield thermonuclear explosion on earth. Its neutron density was ten million times greater than a supernova, Cowan remarks, making it “more impressive in that respect than a star.” The Little Boy uranium gun that destroyed Hiroshima was a thousand times less powerful. Mike's fireball alone would have engulfed Manhattan; its blast would have obliterated all New York City's five boroughs. More than 75 percent of Mike's yield, about eight megatons, came from the fission of the big U238 pusher around the secondary; in that sense it was less a thermonuclear than a big, dirty fission bomb. Fission-fusion-fission, the staging arrangement came to be called. If Los Alamos had devised a way to burn unlimited quantities of thermonuclear fuel, it had also devised a way to burn unlimited quantities of cheap ordinary uranium.
Edward Teller had not traveled out to Eniwetok to watch his former colleagues explode the thermonuclear device that he and Enrico Fermi had conceived in the early days of the Manhattan Project, that he had fought for
