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Hiroshima was destroyed in a flash by a bomb dropped from a propeller-driven B-29 of the U.S. Army Air Corps, on the warm morning of Monday, August 6, 1945. The bomb was not chemical, as bombs until then had been, but atomic, designed to release the energies that Einstein had described. It was a simple cannon-type device of the sort that today any number of people could build in a garage. It was bulbous and black, about ten feet long, and weighed ninety-seven hundred pounds. It fell nose-down for forty-three seconds and, for maximum effect, never hit the ground. One thousand nine hundred feet above the city it fired a dull gray plug of highly enriched uranium down a steel tube into a receiving lump of the same refined material, creating a combined uranium mass of 133 pounds. In relation to its surface area, that mass was more than enough to achieve "criticality" and allow for an uncontrollable chain of fission reactions, during which subatomic particles called neutrons collided with uranium nuclei, releasing further neutrons, which collided with other nuclei, in a blossoming process of self-destruction. The reactions could be sustained for just a millisecond, and they fully exploited less than two pounds of the uranium atoms before the resultingheat forced a halt to the process through expansion. Uranium is one of the heaviest elements on earth, almost twice as heavy as lead, and two pounds of it amounts to only about three tablespoonfuls. Nonetheless the release of energy over Hiroshima yielded a force equivalent to fifteen thousand tons (fifteen kilotons) of TNT, achieved temperatures higher than the sun's, and emitted light-speed pulses of lethal radiation. More than 150,000 people died.
Their executioner was an ordinary pilot named Paul Tibbets, who was twenty-nine then and is still alive now, in Ohio. He neither abhorred nor enjoyed the kill: he was a flight technician, removed from the slaughter by altitude and speed, and coddled by a pressurized, well-heated cockpit. That morning the sky was quiet, with no sign of enemy opposition. The B-29 cruised thirty-one thousand feet above the city in smooth air. It lurched and nosed upward when the bomb fell clear. Tibbets banked steeply to get away and turned the airplane's tail on the destruction. When the bomb ignited, now far behind and below, it lit the sky with the prettiest blues and pinks that Tibbets had ever seen. The first shock wave came shimmering through the atmosphere and overtook the airplane from behind, causing a sharp bump measured at 2.5 g's by a cockpit accelerometer. The bump felt about like the near miss of an antiaircraft burst, or the jolt of crossing a pothole in a jeep. A second shock wave then hit, but it was a reflection off the ground, like an echo of the first, and therefore even less intense. Tibbets tasted the fillings in his teeth. He saw the cloud rising over Hiroshima, and, as must be expected, he felt no regrets.
Still, Hiroshima was not good for him. Though he became a brigadier general in the U.S. Air Force, and later the chairman of an executive-jet company, he suffered from the stigma of having killed so many, and he grew bitter about any implication that what he had done was wrong. It was unrealistic and probably unfair to expect him to repent, but over the decades American elites did just that, having first required him to drop the bomb. In his retirement he took to traveling around the country giving talks to war buffs and like-minded reactionaries. He showed up at air shows, I suppose to shake hands. In the 1990s, he waded angrily into a minor controversy about the Smithsonian's display of the forward section of his airplane, the Enola Gay, and accused the elites of manipulating public opinion for their self-interest. He said he was a pilot and soldier, and by implication a simple man. He sold trinkets on the Internet, including, for $500, a beautifully rendered one-twelfth-scale atomic-bomb model mounted on a (solid, not veneer) mahogany base, and accompanied by an autographed data plate. For those with smaller budgets, he offered a sheet of thirty-six commemorative stamps picturing a B-29 soaring beyond a mushroom cloud, with excellent detail of boiling smoke on the ground. Tibbets may have been bullheaded, but at least he was consistent. When the writer Studs Terkel interviewed him in 2002, eleven months after the September 11 attacks, he did not bemoan the sadness of war or ruminate on the difficulty of facing a stateless foe, but opted true to form for a nuclear response. Against Kabul? Cairo? Mecca? He said, "You're gonna kill innocent people at the same time, but we've never fought a damn war anywhere in the world where they [he meant we] didn't kill innocent people. If the newspapers would just cut out the shit: 'You've killed so many civilians!' That's their tough luck for being there."
Tibbets spoke from experience, and in a narrow sense he was right: it was indeed just tough luck for all the innocents who died under his wings in 1945. Those people, however, did not constitute collateral casualties-any more than the victims in the World Trade Center did. In fact Hiroshima had been chosen primarily as a civilian target and had in part been exempted from conventional firebombing to preserve it for the most dramatic possible demonstration of a nuclear strike. Three days later, the city of Nagasaki was hit by an even more powerful device-a sophisticated implosion-type bomb built around a softball-sized sphere of plutonium, which crossed the weight-to-surface-area threshold of "criticality" when it was symmetrically compressed by carefully arrayed explosives. A twenty-two-kiloton blast resulted, Though much of the city was shielded by hills, about seventy thousand people died. Quibblers claim that a demonstration offshore, or even above Tokyo harbor, might have induced the Japanese to surrender with less loss of life-and that if not, another bomb was ready. But the intent was to terrorize a nation to the maximum extent, and there is nothing like nuking civilians to achieve that effect.
It's too bad, but such is the world we live in. And cities are soft targets. More accurately, they are flammable, dense, and brittle. This goes for New York, with all its high-quality concrete and steel, and even more for the new urban conglomerations of Asia. Beyond this there are significant differences in the dynamics of nuclear blasts, dependent largely on the size of the explosion and the altitude at which it takes place. A Hiroshima-sized terrorist attack at street level in Times Square would shatter midtown Manhattan and raise a cloud of radioactive debris which would settle downwind, lethally, perhaps across Queens. By comparison a North Korean airburst of the same size a half mile above Seoul would cause still larger destruction, but result in less radioactive fallout. These variations, however, become mere details when they are measured against the common result: any city hit by a nuclear bomb will fall badly apart. And a Hiroshima-sized device now lies well within the capacities of any number of nations.
When such a device ignites, the nuclear chain reaction endures for a millionth of a second. During that interval, a lethal burst of neutron particles shoots outward, penetrating walls and people in the immediate vicinity, but losing energy within a few hundred yards, as the neutrons collide with the air. Simultaneously, and for seconds afterward, a pulse of electromagnetic gamma rays, similar to light but far more powerful, flows at dangerous levels through the city to a distance of about two miles. All this would be serious enough, but it is just the start. Even in combination, these two forms of radiation (known as the initial radiation) account for only about 5 percent of the energy, released by the bomb. Another 10 percent is released well after ignition, by the radioactive residue that may fall to the ground or go drifting off through the atmosphere. But all the rest of the bomb's energy-85 percent of the yield-is transformed into airblast and heat. Nuclear bombs of the Hiroshima size destroy cities by smashing and burning them down.
These primitive effects kill almost everyone who would otherwise be dying quickly of acute radiation, then spread out to kill many more. They begin within less than a millionth of a second, when the fission process releases massive amounts of invisible X-rays, which at low altitude are absorbed by the air within a few feet. The resulting heat, rising to tens of millions of degrees, raises the pressures within the vaporizing weapon to several million times that of the surrounding atmosphere. Still within the first millionth of a second, an ultrabright fireball forms, consisting of gasified weapons residues and air. The fireball brutally expands and simultaneously rises. Within three seconds of a twenty-kiloton explosion, it reaches its maximum size, about 1,500 feet across. If it touches the ground (whether because the ignition point was on a street, or at less than 750 feet overhead), it vaporizes the earth and all structures that it encounters and begins to loft large quantities of dirt and debris into a violently rising, intensely radioactive column.
Rising in that column along with all the ash and earth are hundreds of by-products of the fission, many of which are radioactive, but a good number of which decay so rapidly that they reach the end of their radioactive lives before they settle again to the ground. Rapid decay is a common characteristic of the most radioactive fission by-products. Seven hours after ignition, the emissions of the fallout are approximately one-tenth as strong as at the one-hour mark; after two days, the radioactivity has bled away to merely one-hundredth of the same one-hour value. Such decay accounts for the fact that people living downwind under even the thickest fallout will probably be able to escape safely (though they may suffer medical consequences in the long run), if only they can avoid exposure, for the first few hours following the blast. Avoidance is difficult for those not specially prepared to protect themselves, and as a result many people will grow sick or die from the fallout. But residual radioactivity turns out not to be the greatest danger of a twenty-kiloton bomb.
So back to the first small fraction of a second. As the fireball grows, it reradiates some of the energy in the form of two thermal pulses. The mechanisms behind these pulses have to do with the intense temperatures and internal dynamics of the nuclear fireball, the understanding of which must surely rank among the most coolly analytical of practical human knowledge. The first pulse is short and weak and accounts for only 1 percent of the fireball's thermal radiation. It consists of ultraviolet waves, and at a short distance may sunburn human skin but poses no serious danger except for damage to the eyes of the few people who happen to have been focusing in exactly the wrong direction at exactly the wrong time. By contrast the second pulse is massive, accounting for all the rest of the fireball; thermal radiation, and continuing for an eternity-perhaps two seconds. It consists primarily of visible light and infrared emissions and, in a nuclear explosion even of this relatively modest size, is capable not only of burning eyes and skin, but of igniting combustible materials and wooden structures as far as a mile ahead of the fireball's front.
Then comes the blast. It begins as a shock wave at the fireball's birth and propagates outward initially at supersonic speeds. Within the first tenth of a second it overtakes the now slowing expansion of the fireball and bursts through the fireball's surface. Sharply pressurizing and heating the atmosphere, the shock front slows to the speed of sound and continues outward, with enormous destructive power. If the bomb was exploded in the air, there are actually two shock waves, the primary one, then a reflection off the ground. Roughly one and a quarter seconds after detonation, and a third of a mile away from the ignition point, the reflection catches up to the leading shock wave and merges with it into a single vertical front. If the bomb was exploded on the street, as it might be, say, in New York, there is no reflective wave, and the shock front travels from the very start as one. Either way the effects are about the same. Though people can withstand greater pressure spikes than the shock wave delivers, the structures they inhabit cannot. Three seconds after detonation, the shock wave is just under a mile from the ignition point and, in the case of a twenty-kiloton bomb, is breaking structures with a hammer blow of air pressure, and then tearing them apart with outflowing winds of 180 miles an hour. The violence is such that fires that may have been ignited by the thermal pulse are snuffed out. Ten seconds after detonation, the shock wave has moved two and a half miles out and has weakened significantly, but is still capable of making projectiles of glass, tearing doors from their frames, and collapsing some concrete or cinder-block walls.
There is a moment of calm.
The fireball is no longer visible, but it is still extremely hot, and it is vigorously rising into the atmosphere. A result of its rise, and of a partial vacuum that has just been formed by the displacement of air, the winds now reverse and begin to flow back toward the epicenter at speeds up to two hundred miles an hour, ripping apart damaged structures that have somehow so far remained standing. These "afterwinds" raise dirt and debris into the base of the telltale mushroom cloud now beginning to form. The broken city lies like kindling, and whether because of electrical shorts or gas pilot lights, it begins to burn. Depending on conditions, the fires may spread and join, to create the sort of firestorm that was seen in Hiroshima, though not Nagasaki. Either way, the destruction of the city is complete, and in overfilled places such as New York or Seoul-or Mumbai-it is likely that several hundred thousand people have lost their lives.
From the start in the 1940s, the physicists who developed these devices understood the potential for physical miniaturization and a simultaneous escalation in explosive yields past the twenty-two kilotons of Nagasaki, and indeed past a thousand kilotons, into the multimegaton range-the realm, when multiplied, of global suicide. Moreover they realized that the science involved, however mysterious it seemed to laymen, had already devolved into mere problems of engineering, the knowledge of which could not be contained. Within a few years humanly, would face the risk of annihilation-an objective reality that compelled those who understood it best to go public with the facts. In the months following the Japanese surrender, a group of the men responsible for producing the bomb-including Albert Einstein, Robert Oppenheimer, Niels Bohr, Leo Szilard, and others-created the Federation of American (Atomic) Scientists (FAS) to educate U.S. political leaders and the American public about the realities of nuclear weapons. Washington at the time harbored the illusion that America possessed a great secret and could keep the bomb for itself to drop or not on others. The founders of the FAS disagreed. They argued that with the destruction of Hiroshima the only two significant questions had emphatically been answered: could a practical and deliverable device actually be built, and if so would it be put to use? The attempt to go through with the construction of an atomic bomb-to do it for real, and particularly to manufacture the few hundred pounds of bomb-grade fuel that were necessary-had amounted to a national-scale gamble that only the United States could have risked during war in advance of affirmative answers to those questions. But now that Hiroshima had demonstrated the practicality of the venture, the calculation had changed, and it was obvious that other nations could make the investment in full certainty of the return. Some would be friends of the United States, and some would be enemies. Any number of physicists and engineers worldwide were capable of guiding them through the process. The FAS warned the American people in stark and simple terms. In essence they said that the whole world would soon be nuclear-armed. They said, there is no secret here, and there is also no defense. The nuclear age is upon us, and it cannot be undone.
Excerpted from THE ATOMIC BAZAAR by WILLIAM LANGEWIESCHE Copyright © 2007 by William Langewiesche. Excerpted by permission.
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