Even still, attaining the required distance was going to necessitate some precision piloting, and one more calculation. Tibbets had just recently learned about E = mc2 and what it meant for atomic bombs, but he wasn’t too much concerned with that equation. He left E = mc2 to the physicists. He had another equation to grapple with:
Optimal Angle of Departure = 180° − cotangent(r/d) × 2
In this equation, r stands for the plane’s turning radius, and d is the lateral distance of the bomb’s movement once dropped; that is, d is the forward distance that the bomb would be expected to move after it was released from the plane.6
It might appear at first that this math should be unnecessary. Intuition suggests that the ideal piloting strategy would simply be to approach the target from upwind, using the tailwind to maximize air speed, then drop the bomb and just keep going straight at top speed. But in reality that strategy has two problems. First, by moving with the wind at high speed, there would be a price to pay in terms of accuracy in hitting the target. To maximize bombing accuracy, approaching into the wind is best. It slows the plane and gives the bombardier time enough to adjust his sites before releasing the payload. Second, dropping a bomb without changing course means that the bomb’s forward momentum is carrying it directly underneath the plane for a time, literally chasing the plane and its crew as they scramble to get out of town.
The best bombing strategy would actually be to approach from downwind, drop the bomb, make a 180-degree turn on a dime, and accelerate out with the wind at your tail. The problem with this plan is that planes don’t turn on a dime. For any given airspeed, they have a minimum turning radius specific to the plane model. The reality is that, after a plane releases a bomb, the bomb moves forward as the plane starts to make its turn. At some point the turning plane is broadside to the forward-moving bomb, and then the nose of the plane starts facing away from the bomb. Somewhere during the turn the plane is facing directly away from the bomb, and that’s the point when the pilot needs to stop turning and hit the gas. But what precisely is that optimal turning angle? That’s where the equation above comes in. It told Tibbets that the needed angle was exactly 155 degrees. So that’s what he would do: make a 155-degree turn and then rev those engines.
And what was it exactly that Tibbets’s plane was running from? Was it the bomb’s burst of radiation, moving toward the plane at the speed of light? No, the real foe was moving much more slowly. Tibbets was outrunning the bomb’s shock wave, which would be following the plane at approximately the speed of sound. It was the shock wave and not the radiation that would potentially bring the plane down, and that fact would buy him even more time to save it. The speed of sound is 768 miles per hour (1,236 kilometers per hour) not too much faster than a B-29, which had a top speed nearly half of that. So even after the blast occurred, it would take some time for the shock wave to overtake the plane, allowing Tibbets to put even more distance between himself and ground zero.
The angle of departure was critical to safe return. Everything hinged on Tibbets’s ability to make a perfect 155 degree turn in a B-29 and bring the plane to top exit speed as quickly as possible. It was something that Tibbets would practice again, and again, and again, knowing his life and the lives of his crew depended on it.
Although release of radiation is an added hazard of atomic bombs, their destructive power is still mostly through percussive effects (shock waves) and incendiary action (fire). This makes them similar to conventional bombs in the way they kill people and damage property. Most buildings and other man-made structures cannot withstand a shock wave greater than 5 psi. (The term “psi” stands for pounds per square inch and is a measure of the strength of the shock wave.) This fact led to the 5 psi rule, which allows prediction of the destructive area of a bomb based on its known psi profile. Everything within the 5 psi radius from ground zero will probably be destroyed, while structures beyond 5 psi are usually spared.7 Since collapse of buildings and flying debris are responsible for a large proportion of human deaths, the 5 psi radius typically demarcates the area of greatest human fatality as well. Fire produced by bombs is less predictable and can, of course, spread well beyond the 5 psi radius, but it typically moves downwind and is slowed by firebreaks. Radiation is a threat only for those who survive both the shock wave and the fire. But radiation’s killing, like shock waves and fire, behaves according to some rules.
90 DEGREES
Terufumi Sasaki would also be making a turn that would save his life, but he didn’t know this and it required no calculation on his part.8 He made the same turn every day. Sasaki was a 25-year-old physician, recently trained at the Japanese Eastern Medical University and then assigned to the Red Cross Hospital, located on the western side of Hiroshima. To get to the hospital each morning, he first had to take a commuter train from his home, situated thirty miles northeast of Hiroshima, into the city’s center. Then, he switched to a streetcar headed westward toward the outskirts of the city, where the hospital was located. This transfer between transport vehicles amounted to making approximately a 90-degree turn in his direction of travel, and it took him directly away from downtown Hiroshima.
On August 6, 1945, Sasaki completed his commute as usual and arrived at his hospital at 7:40 a.m. The hospital was located 1,650 yards (1,500 meters), or just under one mile, from the Aioi Bridge in the center of Hiroshima. The bridge had a ramp midway that gave it a distinctive T shape, making it highly distinguishable on a map (and from the air) from the many other river bridges that crisscrossed a city built across the highly pronged delta of the Ota River. It’s been said that the city’s shape resembles that of a left hand.9 With palm down and figures spread, the back of the hand would correspond to the main stem of the Ota River, which divides into the fingered waterways of the delta, with fingertips reaching out toward the sea. The T-shaped bridge lay where a wedding ring would be worn.
Sasaki quickly shuffled around the hospital as his workday began. He was headed down a hallway toward the hospital’s testing laboratory with a blood specimen from a patient he had just examined. Sasaki suspected that the patient was suffering from syphilis, a disease with a poor prognosis at the time, but he wanted a lab test to confirm his diagnosis before delivering the disturbing news to the frightened man. At 8:15 a.m., when Sasaki was halfway down a windowed brick hallway, Tibbets completed his 155-degree turn and headed directly away from Hiroshima. All Sasaki would later recall of the moment was that the hallway was instantly illuminated by a brilliant flash of light. If there was any sound involved, it did not make a memorable impression.
7,200 DEGREES
As Sasaki walked down the hospital hallway, 53-year-old office worker Shigeyoshi Ikeda was just sitting down at his desk to begin his day’s work at the Kansai Oil Company. His desk was located within the Hiroshima Prefecture Industrial Hall, in downtown Hiroshima. This concrete building happened to be just 175 yards (160 meters) from the Aioi Bridge. Before the sound of the bomb’s explosion even had time to reach his ears, Ikeda’s flesh was completely vaporized.
Ikeda’s wife and his 11-year-old son went to the building shortly after the bombing in search of his body. All they found was Ikeda’s skeleton, still sitting in his office chair and identifiable only by a few fragments from his pants and his wristwatch. Ikeda’s wife said to the boy, “This is your father.” They packed up his remains, including the watch, and took them home.10
Tens of thousands in downtown Hiroshima met a similar fate that morning, but few of them left any remains, unless they happened to be within a stone or concrete building—the only structures that didn’t completely vanish along with the victims.
The heat from the blast was intense. The fireball at ground zero was estimated to have a temperature of 7,200°F (3,980°C), exceeding the surface temperature of even the sun (about 5,500°F; 3,037°C). It was as though a piece of a star had suddenly appeared on the surface of Earth. This fact would not escape the notice of nuclear bomb physicists.
Even a
t 380 yards (329 meters) from ground zero, mica was found fused to granite gravestones in a cemetery.11 Since mica has a melting temperature of 1,650°F (900°C), the temperature must have been at least that high at 380 yards out. Being that Ikeda was located at less than half of this distance, his body must have been exposed to temperatures well in excess of 1,650°F.
The heat from the bomb directly produced fires that combined with secondary conflagrations caused by debris falling on cooking stoves and electrical wires. Fanning of flames by the high winds that followed the blast produced a firestorm that engulfed about four square miles of the city center,12 an area that included three-quarters of the city’s wartime population of about 245,000 people.13 This roughly circular, burned area had an average radius of 1,500 yards (1,371 meters) from ground zero.
BAD NEWS COMES IN THREES
Sasaki was the only Red Cross Hospital doctor who was unhurt. He was violently thrown down. He broke his glasses and lost his slippers, but was uninjured. Not so for the rest of the hospital’s staff and patients, including the syphilis patient Sasaki had left behind down the hall. He was already dead.
Of the 30 doctors at the hospital, only 6 were able to function. The nursing staff fared even worse; only 10 out of 200 were able to work.14 This small cadre was unprepared for the 10,000 bomb victims that would descend upon the 600-bed hospital before the day was out.15
FIGURE 7.1. THE PEACE DOME. The Hiroshima Prefecture Industrial Hall was one of the tallest concrete buildings in downtown Hiroshima at the time of the atomic bombing. It was also one of the few buildings that had a superstructure strong enough to survive the devastation. The top photograph shows what remained of the building just after the bombing; it towered over the surrounding rubble of buildings that did not survive. The bottom picture shows the same building as it looks today, dwarfed by the surrounding reconstruction of the city. The building has been preserved as a memorial to the atom bomb victims and is currently referred to as the Hiroshima Peace Memorial, or simply the Peace Dome.
As Sakai and the other doctors labored among the wounded, who were quickly spilling over onto the hospital grounds, they found some very odd symptoms. Although most victims had the lacerations, contusions, and abrasions typical for a percussion bombing, there were also blindness and severe burns, even among those who had not been in the firestorm. For some patients, silhouettes of flowers or other decorative patterns on their shirts had actually been etched onto their burned skin.
It had not even occurred to the doctors that radiation might be involved, but on the second day after the bombing, the staff discovered that all stores of x-ray film in the hospital had strangely been exposed, and the reality of the situation then began to dawn on them.16 Sasaki knew little about radiation sickness, although he did know that x-rays had caused such illness among overexposed x-ray workers. But he had never been trained to deal with this illness, and the medical skills he did have were of little use as he tried to treat radiation sickness over the next days and weeks. He simply moved from patient to patient, swabbing burns with antiseptics and bandaging what he could. But no matter what he did, people continued to die.
Sasaki was unable to interpret the underlying disease mechanisms for the strange symptoms he was seeing. We now know that the unusual eye symptoms were not caused by fire or heat of the bomb, but rather by the intense light that the bomb emitted. Although the bomb’s ground zero temperature equaled the sun’s, the light emitted from the atomic bomb detonation was even brighter than the sun.17 This had been anticipated by the physicists. Tibbets’s crew was issued welding goggles to protect their eyes from the blast,18 but only the tail gunner actually witnessed the flash of light because the plane, as correctly calculated by Tibbets, was facing directly away from the blast when it occurred.19
Although the intense visible light was blinding, it was also accompanied by UV radiation, not visible but just as damaging to eyes and skin. This UV radiation, with its wavelengths sandwiched between invisible ionizing radiation and visible light, has properties of both (see chapter 2). Like ionizing radiation, it is damaging to tissues; however, similar to visible light, it penetrates poorly, leaving all its destructive energy in surface tissues.
The story of one bomb victim vividly demonstrates the nature of UV radiation casualties. It was said that two men were riding a bus at the time of the blast, seated one behind the other. One man had his window closed and flying shards of glass cut his body badly when the shock wave hit the bus and broke the window glass. The man behind him escaped the glass injuries because his window was open. So the unhurt man assisted the bleeding one and started to carry him toward the nearest hospital, but on the way their roles reversed. The uncut man’s skin started to become so badly burned that he couldn’t go any further, and the bleeding man then carried the burned man the rest of the way.20
Although it is impossible to verify the authenticity of this story, the details ring true. Windowpane glass is quite effective in filtering out UV radiation. It is likely that the UV radiation, traveling at the speed of light, exposed the unprotected man rather than the one behind glass, but the shock wave, traveling more slowly at the speed of sound, arrived and broke the glass of the bus window seconds after the ultraviolet light had passed. The rapid appearance of the ultraviolet radiation burns suggests that the man’s ultraviolet radiation dose was extremely high. And this detail seems credible as well.
Within a short time, Sasaki’s hospital was filled with such burn victims, some of whom were also vomiting for no apparent reason. Most suspected that the vomiting was caused by a chemical toxin that was incorporated into the bomb, since many people reported smelling a strong “sickening” odor immediately after the blast.
The odor was actually just ozone (O3), the product of the ionization of oxygen gas (O2) in the atmosphere by the radiation. Ozone is produced whenever oxygen is ionized, either by radiation or electricity, and is responsible for the pungent odor one smells after electrical storms. Although some may find a strong smell of ozone nauseating, the majority of the vomiting that people experienced was actually the result of internal radiation injuries, and was simply a prelude to what would come.
For all of Sasaki’s labors, most of his burn patients died. The UV radiation burns were a sure indication of full exposure to all types of bomb radiation—radiation that included not just the visible and UV types, but also the highly penetrating ionizing radiations as well. These ionizing radiations were mostly gamma rays and neutrons, and their health effects would be more insidious and delayed, but no less severe, than the surface burns. The internal radiation injuries were harder to see. Out of sight, out of mind. But just as deadly.
Over the following days, people at the hospital started dying in great numbers, and removing so many bodies became a serious problem. Workers threw the bodies of the dead onto a pyre that had been built outside the hospital. The ashes of the cremated victims were collected and saved for their families. Having no use for x-ray envelopes due to the exposure of all the x-ray films, the envelopes were used to hold the ashes of the dead. The envelopes were labeled with the person’s name and stacked in piles in the main office of the hospital until relatives could be notified.
Even as the radiation deaths continued, the causes of death changed over time, and previously healthy individuals inexplicably sickened even weeks after the bombing.21 As delayed bouts of illness overtook the surviving population, the rumor began to spread among the patients that the atomic bomb had spread some kind of slow-acting poison that would make Hiroshima unlivable for seven years.22 But this was an idea ahead of its time.
Though it was difficult to see at the time of the bombing, Sasaki and his staff later came to realize that radiation sicknesses came in three successive waves, each with its own symptoms. Likewise, each killed in a different manner.
We now know the three waves of radiation sickness represented three subsets of victims suffering from different ranges of radiation dose.23 The first radiation synd
rome was hardest to recognize because it was mixed with the severe physical trauma and skin burns experienced by those closest to ground zero. Nevertheless, against the background of physical injuries, there was a characteristic combination of nausea, vomiting, and headache. Patients with these symptoms expired within the first three days. The exact cause of death was hard to determine because it usually was the result of a combination of both trauma and radiation injury. Still, there were surely some who, one way or another, escaped trauma and burns yet still died within hours or days of the blast. These patients were likely killed exclusively by internal radiation damage. Their location within some building at the time of the blast protected them from flying debris and burns, but only the strongest stone, brick, or concrete buildings could have shielded someone from the penetrating radiation, and few of Hiroshima’s buildings were constructed of those materials.
This first radiation syndrome occurred among those who were closest to the blast and who thus received the highest radiation doses (greater than 20,000 mSv).24 When a human body experiences whole-body radiation doses at this level, all of the body’s cells, including the brain’s nerve cells (neurons), begin to die. Ironically, neurons are among the most radiation resistant of human cells because they never divide; yet, when doses get high enough for even neurons to succumb, it is these resistant cells that precipitate the victim’s rapid death. This is because the brain is critical in controlling all of the body’s physiological functions. As the brain’s neurons begin to die, the brain swells, and coma and death cannot be far behind, as all systems begin to shut down. This first syndrome, found exclusively among the very highly dosed victims, is known as the central nervous system (CNS) syndrome. It is a type of radiation sickness from which none recover, and death comes mercifully soon.
Strange Glow Page 16
