"It’s just like a mule. A mule is a docile, patient beast, and he will give you power to pull a plow for decades, but he wants to kill you. He waits for years and years for that rare, opportune moment when he can turn your lights out with a simple kick to the head.”

—Jerry Poole, referring to a nuclear power reactor

By the start of World War II, which in Europe was 1939, the radium scandals had left the public with a strong and somewhat twisted concept of the dangers of radiation. They saw it as deadly in the worst way. It could originate in invisibly small particles of matter, and by the time you realized that you had been dosed with it, it was too late to do anything about it. Swallowing radium was about as bad as radiation sickness could get, but mankind had not seen anything yet. The intense radiation that could be released by a newly discovered phenomenon, nuclear fission, would put radium contamination in perspective. A couple of accidents with fission made it clear that with the discovery of this new way to release energy came novel ways to bring life to an end.

The entire structure of industrial safety had to adjust accordingly. If this new energy source was to be cleaned up for public use, then there would have to be new materials handling procedures, new laws and regulations on the federal level, powerful new government agencies, new controls on every aspect of this prospective industry, and a great deal of secrecy. Unlike with the radium adventure, entrepreneurs, swindlers, amateurs, and fake doctorates would not feel invited to participate. The world had changed, and simple republican democracy was not what it used to be.

Technically, the first public demonstration of nuclear fission by dropping two nuclear weapons on Japan was not an atomic accident, but these events would permanently harden some opinions and perceptions for future nuclear mishaps. The A-bomb campaign was seen as a sure and quick way to bring the war to an end with a minimum number of casualties, but, to be completely honest, it was also a large-scale science experiment. The only hard data that existed concerning the effects of radiation on human beings were studies of the deaths and injuries from radium ingestion. Most scientists working on completion of atomic bomb development speculated that most of the deaths from their new weapon would be from flying bricks and glass as cities were flattened, and not by the radiation from fission or the radioactive byproducts of fission. Yes, thousands of civilians would die, but how was that different from fire-bombing Tokyo, which had killed over 100,000 people? By the end-time, half the capital city

was in ashes, with care taken not to bomb out the Imperial Palace.25

When the atomic bombs were ready to deploy, just about every city in Japan had been bombed to pieces, with a few exceptions. Hiroshima, Kokura, Niigata, and Nagasaki had been purposefully spared. These were the target cities for the atomic bombings, with Hiroshima at the head of the list. It was a little jewel of a city, with 350,000 residents, the Japan Steel Company, Mitsubishi Electric Manufacturing Company, and Headquarters of the Second Army Group, tasked with defending the island of Kyushu from the coming Allied invasion. It was

untouched and in perfect condition.26 There was no sense in dropping the A-bomb on Tokyo, as there was hardly anything left to destroy, but to hit a spared city would yield data as to the destructive power of a single bomb-strike, aimed right at the center. As an experiment, it would end the speculation and guesswork about the effects of fission radiation on human beings and man-made structures, and it would give a calibration for future military operations. The Hiroshima mission consisted of three B-29 heavy bombers: the Enola Gay, carrying L-11, or “Little Boy,” The Great Artiste, carrying the yield measurement instrumentation, and Necessary Evil, with the observers and the cameras.

Three instrument pods, having parachutes to slow their descent, were dropped from The Great Artiste and synchronized with the bomb-drop from Enola Gay with a radio signal. The pods were equipped with radiation counters and barometric instruments, each with a radio channel sending data continuously back to the airplane, where they were recorded. Necessary Evil had a Fastax high-speed motion picture camera, shooting 7,000 frames per second, and a still camera recording images of the explosion. A debriefing of the crew, after-action photographs at high altitude, and eventual ground-level evaluations came later. The initial data unraveled by the scientists was sobering, and it took some of the euphoric edge off the celebration.

The Little Boy was an “assembly weapon. ”A cylindrical shell made of a stack of uranium rings was blown against a similar stack of smaller rings held stationary in a block of tungsten carbide, using a smooth-bore 6.5-inch gun barrel. The projectile rings, propelled quickly by three bags of burning nitrocellulose, and the smaller cylinder assembled into a larger, complete cylinder of uranium metal, enriched to 86% U-235. The resulting configuration was hypercritical, and it fissioned explosively.

To maximize the “shock and awe,” no leaflets were dropped warning Japan of an impending A-bomb attack, and security was so tight on Tinian Island, the base for atomic operations, that

most of the Army Air Force personnel could only guess what was going on.27 However, the surprise was not as complete as one might think.

Tinian, captured from the Japanese in July 1944, was a sugar-cane plantation just south of Saipan in the Marianas Island Chain. Flat as a pool table, it was an ideal spot for launching heavy bombers against the main island of Japan. Iwo Jima, another small island even closer to Japan, had been recently taken in murderous fighting, and it was used as an emergency landing base for the heavy stream of B-29s flying out of Tinian. The special task of building and testing the nuclear devices was assigned to the 1st Technical Service Detachment of the 509th Composite Group, and they were stationed in isolation from the rest of the Air Force at the extreme northern end of the island. The bomb assembly areas were literally overlooking the Pacific Ocean. This unique job, carried out by a combination of military personnel and civilian scientists, was named Project Alberta.

The island had been thoroughly cleansed of Japanese soldiers before the two airfields were built and the Air Force was moved in, or so it was hoped. Actually, there remained a contingent of Japanese observers, and their only mission was to remain invisible, be aware of everything that was going on, and report these findings by radio back to the home island. The Alberta personnel first became aware of this when a freshly washed shirt, left on a tent to dry, vanished overnight. It had been pilfered by an observer who needed a shirt. Turns out, there was a high area in the middle of the north end of the island, about 440 feet above sea level,

consisting of coral cliffs, pocked with caves and tunnel entrances. At night, the observers would quietly come down out of the caves and into the 509th area to take notes.

These detailed examinations were useful. The next morning, Tokyo Rose, an English-language radio variety show originating somewhere in Japan, would casually mention details about what was going on at the north end of Tinian Island, broadcasting to the entire Allied force. She apparently knew more than the average sailor, and, grappling for an explanation, some seriously credited the charming radio announcer with clairvoyance. The Japanese, from the Imperial Emperor on down, knew that some special weapon was being prepared. It would take few planes to deliver it, and they even knew which planes would fly the mission and when they took off. Was it a new form of nerve gas? Perhaps it was a powerful anesthetic to be delivered by airplane, and the Americans planned to put everyone on the island of Honshu to sleep, then just walk ashore and take over.

Colonel Paul W. Tibbets, the man in charge of the bombing operation, grew concerned at the accuracy of the radio programs, and he had the markings on his plane, the Enola Gay, changed at the last minute. Before the paint had dried, Tokyo Rose announced it to the rest of the listening world, describing the upward arrow in a circle on the tail. Her omniscience could be

spooky.28

At the end of World War II, Hiroshima was a compact Japanese city with several munitions plants, army storage depots, and an army headquarters. Even though most strategically important cities in Japan had been bombed, Hiroshima had been left untouched. One bomb destroyed its industrial capability and wiped out all communications, power distribution, and transportation systems.

After Hiroshima was annihilated on August 6, 1945, the Japanese knew better what was going on, and a commando raid on the F-31 “Fat Man” implosion weapon assembly hut on Tinian was organized immediately. Philip Morrison and Robert Serber were directing the complicated work on F-31, and the hypodermic tube, used to monitor the subcritical activity in the bomb core, had just been installed at mid-morning on August 8. Two segments of the spherical aluminum bomb casing, Y-1560-6 and Y-1560-5, were being bolted together. The atmosphere was getting tense in the hut, and a few of the team members took a break outside, trying to rest under a tree. Looking out to sea, they suddenly noticed an odd-looking ship, approaching about a mile off, to the north. It was diesel-powered, painted completely black, about 150 feet long, with the deck five feet above the waterline. It was devoid of markings but was flying a tattered American flag. Swimmers were diving off the deck, at about 100-foot intervals, and making for shore. By the time the ship had passed the assembly hut, at least 30 swimmers were in the water, with more peeling off the deck. A security guard on the embankment opened up with a machine gun, firing over the heads of the assembly techs and aiming for the bow.

It was strange that they tried this stunt in broad daylight. Had they been delayed by several hours and missed their insertion schedule? The ship hove a hard right and headed out to sea, picking up what few swimmers it could. Clearly, a desperate attempt to sabotage the next A-

bomb had failed.29

As a demonstration of the overwhelming strength of the Allied invasion force bearing down on Japan, dropping a uranium bomb on Hiroshima was unsurpassable. The mechanics of the A — bomb explosion have been thoroughly studied, and here is a summary:

The nuclear fission explosive uses the fact that a uranium-235 or plutonium-239 nucleus can split into asymmetric fragments when it encounters a loose neutron. This unusual reaction releases about 200 MeV of energy, which on the atomic scale is a great deal. Also emerging from this mini-explosion are two extra neutrons. These neutrons, traveling at high speed, crash into other nuclei in the tight matrix of a bomb core, which consists of a metallic mass of the fissile material. The first reaction thus accelerates into two reactions, and each generation of reaction leads to twice as many subsequent reactions. In fewer than 90 such generations, every nucleus in a 50-kilogram uranium bomb core will experience the fission stimulus, and the combined reactions release the energy equivalence of exploding a million tons of TNT high explosive. Given the speed of the flying neutrons, the size of a bomb core, and the response time of a uranium nucleus, these 90 generations take place in about one millionth of a second. The short time in which this much energy lets go provides the condition for a hell-on-earth

explosion.30

Most of the energy from this explosion, 85 percent, is released in the form of heat. The heat radiates as light energy, from infrared to ultraviolet. The remaining 15 percent of the energy release is radiation of nuclear origin, but only five percent is immediately involved. Residual radiation, ten percent of the bomb’s energy, is released on a falling exponential rate over

thousands of years after the instant of detonation.

The World War II bombs, the only nuclear devices ever used as weapons so far, were

airbursts, detonated at about 1,900 feet above the ground.31 The air surrounding the bomb instantly heated to incandescence. This feature is called “the fireball.” This rapidly expanding sphere translated a percentage of the thermal energy into blast energy, or a destructive wave of compressed air moving outward at high speed, capable of knocking over concrete buildings.

о iwmng

Fat man was completely different from Little Boy in the method it used to create a hypercritical mass and the fissile material used. A ball of plutonium metal the size of a navel orange was momentarily compressed to the size of a table tennis ball using a powerful explosion turned inward. Although the high explosives surrounding the plutonium ball exploded outward like an ordinary bomb, the inward force of the same explosion was carefully directed into a spherical shock wave. The inter-nuclear distances in the plutonium were shortened by the shock wave, and the resulting hypercritical mass fissioned explosively.

The first thing hit by this airwave was the ground directly underneath the bomb, or “ground zero.” This was a hard thump, and it resulted in an earthquake-like shock energy traveling outward through the ground. The total energy from the detonation was thus distributed as 50 percent blast and shock, 35 percent thermal radiation, 10 percent residual nuclear radiation, and 5 percent initial nuclear radiation. The scientists had not been wrong in predicting small damage due to nuclear radiation, but they had been way off in considering the damage done directly and indirectly by the intense thermal energy. The burns that injured many survivors of the A-bombs were not caused by gamma or beta rays, but by light. Simply being caught standing behind a light-shield when the bomb detonated could be life-saving, providing you weren’t struck down by the shield as it was blown away seconds later in the air blast. The temperature at the center of the explosion was far outside human experience, probably millions of degrees, approaching the conditions in the center of the sun, and the air pressure produced was on the order of millions of pounds per square inch. Everything flammable within 12 miles caught fire. Some people were vaporized in the fireball, tens of thousands were crushed in the air blast, and tens of thousands more were severely burned by the flash of light. The death-toll
would eventually reach about 83,000 people, as some would die decades later from radiation — induced cancer.

The heat and initial nuclear radiation portions of the event were over in about 60 seconds, but the bomb effects continued to develop for 6.3 minutes. The rapidly expanding fireball created a large vacuum in midair, and as the heat dissipated, air from the surrounding territory started to be sucked in. The blast thus blew air both ways: first outward, a pause, then inward, back toward ground zero. This effect is called the “afterwind.” Meanwhile, the residual heated air rose in a strong updraft, like a hot-air balloon. Solid material on the ground, now pounded to dust, was drawn up into the rising column, making a dirt-cloud.

In thirty seconds, the cloud reached a height of three miles. When the ever-rising cloud reached an altitude where its density matched that of the surrounding air, at the base of the stratosphere, the cloud started to spread out horizontally. The sight of this feature became an icon, a dreaded emblem of the atomic age—the mushroom cloud.

On August 9, 1945, the Strike Centerboard operation, carrying the Fat Man plutonium implosion device in a B-29 named Bock’s Car, dropped the second weapon on Nagasaki, and

World War II was over except for the shouting.32

To develop these science-fiction-level devices into things that could fall from an airplane required a crash program of unprecedented speed and complexity. Not only was the nuclear reactor invented, prototyped, powered up, and operated for three months, but a huge reservation was built in Washington State so that several reactors could be run 24 hours a day at high power, experimental reactors were built and operated in Tennessee and Illinois, massive plutonium and uranium purification plants were built and run, and risky physics experiments were conducted in New Mexico, all without a single fatal accident or even a radiation injury. Thousands of people worked on this project, some in hazardous conditions and most without a clue as to what they were building. The effort was constantly plunging ahead into the unknown, and the potential for disaster was always close; but due to heightened vigilance and a touch of luck, nobody got hurt. There are no atomic accidents in the Manhattan Project on which to report, right up until the last bomb was dropped. There were, however, some close calls that could foretell later problems.

About 25 miles west of Knoxville, Tennessee, was a sparsely populated 60,000 acres of land near the Blackoak Ridge. Blackoak runs north-south and connects two bends of the Clinch River, and it is part of a sequence of five ridge/valleys on the southeast side of the Appalachian Mountain Range. The Cherokees claimed it as a hunting ground, but by 1800 the Treaty of Holston had ceded it to the United States and several farming communities took root in the area.

In 1902 the local mystic, John Hendrix, 37 years old and thought by some to be not right in the head, was enjoying a typical day by lying in the woods on the ground clutter and gazing up at the sky through the trees. His attention was grabbed by a loud voice, telling him to remain there asleep for 40 nights so that he could be shown visions of what was in store for the surrounding acreage. Being given an account of the future by an external source, he repeated this information many times to anyone who would listen. His predictions were positively eerie:

And I tell you, Bear Creek Valley someday will be filled with great buildings and factories, and they will help toward winning the greatest war that ever will be. And there will be a city on Black Oak Ridge and the center of authority will be on a spot

middle-way between Sevier Tadlock’s farm and Joe Pryatt’s place. A railroad spur will branch off the main L&N line, run down toward Robertsville and then branch off and turn toward Scarborough. Big engines will dig big ditches, and thousands of people will be running to and fro. They will be building things, and there will be a great noise and confusion and the Earth will shake. I’ve seen it. It’s coming.

Hendrix went on to inhabit a mental institution, and in October 1942 Brigadier General Leslie Groves, head of the Manhattan Engineer District and assigned the task of developing an atomic bomb, chose a spot between the Tadlock and Pryatt farms in

33

east Tennessee as his headquarters. It was remote, cut off from the world, and yet blessed with a great deal of surplus electrical power. The Tennessee Valley Authority, set up by President Roosevelt as a make-work project in the throes of the Great Depression, had gotten a little too enthusiastic and peppered all of east Tennessee with hydroelectric plants. Groves would quickly put them to good use.

Nobody among the Axis Powers that were trying to take over the world had ever heard of the place, and it wasn’t even on a map. It was perfect for top-secret work. In a couple of years, it would be known as the Manhattan District HQ, the Clinton Engineering Works, or simply as Oak Ridge, and its population would explode into 75,000 people. Tracks were laid for a rail spur off the L&N, right where Hendricks had said, and in Bear Creek Valley was erected an enormous industrial complex of seven buildings comprising the Y-12 site. The largest building in the world, the half-mile-long K-25 gaseous diffusion plant, was built at a bend in Poplar Creek,

about 10 miles southwest of Y-12.34 Construction began at a furious pace, making an instant city. Housing for workers, thoughtfully made of asbestos to prevent fires, was a priority. Eventually the city had ten schools, seven theaters, 17 restaurants, 13 supermarkets, a library, a symphony orchestra, churches, and its own Fuller Brush salesman.

This bustling metropolis was built from scratch for exactly one purpose: to take mined uranium, which was nearly all worthless uranium-238, and purify it down to the rare and precious ingredient, uranium-235. The atomic weight of this isotope, 235, was an odd number, and that made its heavily overloaded nucleus touchy and likely to explode if a random neutron were to blunder into it. Just any neutron would do, but it was particularly sensitive to slow neutrons, beaten down to move no faster than any common molecule at room temperature. At Y-12, K-25, and S-50 various concentrations and chemical forms of uranium-235 were stored, moved, stacked up, bottled, boxed, and formed into piles. Only the few top administrators and some of the on-site scientists knew what the stuff was for and had a vague sense of the ultimate danger of working with it. There were 12,000 workers in the K-25 building alone, and none of them was made aware of exactly what they were doing.

For the needs of military security, there was nothing better than absolute ignorance. It was impossible for a worker to spill the beans to an Axis spy, even on purpose, and this massive, continent-wide industrial effort to build atomic bombs remained unknown to the enemy powers. However, there were dangers in this enterprise that had never before visited the human race. If one happened to stack up enough of this weird material in one place, it would start to generate heat, and this energy release would increase exponentially until the stack lost its initial configuration. The conditions under which this disaster could happen were varied across multiple dimensions. The “critical mass” condition depended on the purity of the uranium-235 in the material. Uranium fresh out the ground had only 0.73 percent of the active isotope in it, and an infinite stack of it would not approach the energy production threshold. Start increasing the percentage to, say, 3.0 percent, and the probability changed. If the uranium were dissolved in ordinary water, as it often was in the stages of processing it, then the hydrogen in the water would slow down the trigger particles, the free-range neutrons, using collision dynamics. Just like a high-speed neutron hitting a hydrogen atom in water, if you crash your car into one parked, your car stops cold and the one you hit bounces excitedly into whatever is in front of it. In the same way, a high-speed neutron crashing into a slow-moving hydrogen nucleus, which is of similar mass, will kill the speed of the incoming particle. Having uranium dissolved in water,

even if it’s only slightly enriched, makes a runaway fission situation quite possible.35

Another factor is the shape of the stack. The less surface area your stack has per volume of the stack, the better is the probability of causing an energy-release incident. The worst you can do is to stack bottles of enriched uranium oxide dissolved in water, which is a curious green color, in a rounded mound on the floor. In that configuration the surface area is minimized, so fewer neutrons, which bounce around in completely random directions, are likely to escape the stack without causing a fission. Next worse is a neat cube. The best way to stack it is in a straight, single-file line. The same number of bottles can either be benign containers of mineral water or a glowing inferno, depending on how you stack it.

Bricks of pure uranium metal are another matter of concern. Power-producing fission is possible using high-speed neutrons as triggers, freshly minted in the fission process, but the probability is lower. In pure metal, neutrons were not slowed down to desirable speed just by running into atoms. Hitting a uranium nucleus was like running your car at high speed into the side of a bank building. You might make the building move, but not by much, and your car bounces off in the opposite direction with most of its initial speed. It takes more enriched uranium mass in pure metal form to make it go nuclear than in a water solution, but that’s not to say it does not happen. Stack up enough enriched uranium metal in a shape that will encourage fission, and you have it melting through the floor.

Technically, this type of potential accident builds an impromptu nuclear reactor, and not a nuclear weapon. There is no way to stack up pure uranium bricks fast enough for them to explode as a bomb, because an entire explosion takes place in about a microsecond, much faster than anyone can lay down blocks. But such a situation of stacking enriched uranium bricks would still be extremely dangerous, as it would make a basic nuclear reactor without bio­shielding and without even rudimentary controls. It runs wild until the heat generation is sufficiently severe to wreck the stack and make it subcritical by virtue of shape.

The behavior of the water-solution stack and the solid-metal stack are significantly different. In a water stack, the power generation is dependent on neutrons slowed to thermal speed. Not only are the neutrons slowed down, they are separated by distance from uranium nuclei in the dilute water solution. The reactor is spread out over a large volume, the size of a garbage can. The metal reactor has more uranium in it, but it is extremely compact. In the optimum configuration, a sphere, it is the size of a grapefruit, and it is extremely sensitive to its environment. If you have a barely subcritical sphere of uranium-235 sitting on a tabletop, not fissioning or causing any radiation to speak of, then simply walking by it or waving a hand over it will cause it to go supercritical, raising its temperature and spewing out radiation in all

directions, increasing exponentially.36 This happens because your body consists of about 70 percent water. Random neutrons, born of spontaneous fissions and escaping off the surface of the sphere, will hit your hand occasionally and slow down in your water component. Those occasional neutrons are knocked in all directions. A scant few wind up drifting back toward the sphere from which they came. They re-enter the fissile material, and this extremely slight increase in the number of available slow neutrons can set off a chain reaction. The neutron population bursts into high production, and it’s off to the races.

Incredible as it seems, the difference between the subcritical neutron population in a uranium mass, making no fission, and supercritical, making wild, increasing fission, is a very small number of available neutrons out of trillions: all it takes is just one neutron.

A similar possibility of accidentally assembled reactors existed at the Hanford Works, built a year after the Oak Ridge facility out in the desert in the middle of Washington State. It was another instantly derived city, a bit larger than Oak Ridge, having 50,000 people. Its product was plutonium-239, an artificially produced isotope made by subjecting uranium-238 to neutron bombardment. The fissile material was nearly 100 percent pure, and having low enriched material was never a problem. In water bottles or stacked in bricks, it was as problematic as pure uranium-235 and much more plentiful.

At Oak Ridge in 1944, batches of enriched uranium began to accumulate, and a memo arrived at Los Alamos from a plant superintendent, expressing concern about the possible peril of having bottles of uranium-water solution neatly stacked in a corner. Would it be advisable to install a special fire extinguishing system? This memo set off alarms on multiple levels, and J. Robert Oppenheimer, head of the scientific mission to develop the A-bomb, dispatched Emilio Segre to Tennessee to assess the situation.

Segre was a typical worker at Los Alamos, in that he was a brilliant physicist and a recent immigrant from fascist Europe, having been driven away by the enforcement of official anti­Jewish regulations. He would eventually win the Nobel Prize in physics and discover two new elements and the antiproton, but in 1938 he was a refugee stuck in a $300-per-month job as Research Assistant at Ernest Lawrence’s Berkeley Radiation Lab in California. When Dr. Lawrence, who believed strongly in fiscal responsibility, figured out that Segre had nowhere else to go, he dropped his salary to $116 per month. The talented Segre felt fortunate to have been grabbed by the U. S. Government to work on the bomb program in New Mexico. As head of the experimental division’s radioactivity group, Oppenheimer thought he could spare him for a few days to see what was going on in Tennessee.

Examining the situation at Oak Ridge, Segre found that no workers knew that they were making an explosive, much less that it was a very tricky one, and only a few top officials were aware of the problem of bringing together a critical mass. They had been given the talk, but it had mentioned only the problem of stacking metal bricks, and they had no idea that water diluting the active substance only made it easier to produce a runaway reaction. The accumulating stores of wet uranium at Oak Ridge were on the verge of disaster. Oppenheimer responded to Segre’s grim report by dispatching his best man, Richard Feynman, immediately to the scene.

Feynman was only 27 years old, the youngest group leader in the mass of heavy thinkers gathered at Los Alamos. Working under the director of the theoretical division, Hans Bethe, he was one of the few natural-born Americans on the T-section payroll. He grew up in Far Rockaway, New York, and earned his physics degrees at MIT and Princeton. He had quickly established a reputation as a quick mind with brilliant insights and an ability to find the problem in any aspect of the complex bomb development. He also gained fame by an apparent ability to crack any combination security lock at the lab. Everyone was impressed, particularly Oppenheimer, who was not disappointed by Feynman’s sharp analysis of the problem.

It was even worse than Segre had reported. There were storage drums of different sizes stored in dozens of rooms in many buildings on site. Some held 300 gallons, some 600 gallons, and some an eye-opening 3,000 gallons of uranium oxide dissolved in water, in a range of uranium-235 enrichments from raw, natural uranium to nearly critical concentrations. Some were on brick floors, which was fine, but some were on wooden floors. Wood is an organic compound, and it contains hydrogen, which would moderate the speed of leaking neutrons and reflect them back into a drum, enhancing the conditions for fission. In some cases large drums were segregated into adjoining rooms, but if two drums were backed up against the same wooden wall, the two subcritical nuclear reactors were capable of coupling into one critical assembly, using the wall as a neutron-moderating connection.

Atop all those problems, the very shape of a drum encouraged fission. Drums were made to minimize the amount of metal needed to build a container of a given size, so the volume-to — surface-area ratio was optimized. Feynman examined the floor layouts of the agitators, evaporators, and centrifuges used in the sequential processing of the uranium. From the blueprints of the buildings, he could tell that the architects did not have nuclear physics in mind when they drew the floor plans. The entire industrial complex of the Clinton Works was a disaster under construction. The potential meltdown, in which a nuclear reactor could be unintentionally assembled and run up to power, was given a name: the criticality accident.

There was no set rule for how much uranium water could be stored in one location, or how close two drums could be located. There were simply too many variables at work to be able to look in a room and say, “Put one more drum in here, and it will take an aerial photo to see the

entire crater.”37 Feynman relished the task of mathematically solving the impossibly complex interactions of bricks of metal near steel drums scattered in random locations in connected rooms, but the problem boiled down into one fact: the workers in this production facility could not be kept unknowing of what was going on. Some raw knowledge was the key to preventing a nuclear disaster. Oppenheimer gave him the go-ahead. The rabid security measures were now working against the project, and this would have to be an exception to the total ignorance policy, or the uranium and plutonium production could self-destruct. Feynman prepared a series of lectures for workers and supervisors, starting with the simple basics of nuclear physics. This action probably saved many lives, but in the next few decades the lesson would have to be learned over and over, continent by continent.

Aside from the usual industrial accidents and hazards of using dangerous chemicals, working

at a nuclear facility under war footing was remarkably safe. There were no radiation injuries.38 However, there was a reactor explosion that destroyed a building. It was not in the Western Hemisphere, and, as would prove the case in many future nuclear accidents, the reactor was nowhere near running on fission. The problem involved water.

Werner Heisenberg, a respected German theoretical physicist, had made a name for himself well before the war started. He was famous for having expanded quantum mechanics with his uncertainty principle and his matrix spin operator, and he won the Nobel Prize in physics in 1932 for “the creation of quantum mechanics,” which was a bit overstated. With the German universities cleansed of nuclear talent by Nazi anti-Jew policies in the 1930s, Heisenberg, a

Lutheran, was almost all that was left for mounting a nuclear weapon project. The necessary tasks were parsed and funded by the Reich Research Council. Nicholaus Kopermann was in charge of uranium production. Paul Harteck got heavy water production. Walther Bothe drew nuclear constants measurement, and Georg Stetter was given transuranic elements. Heisenberg was assigned the core problem, to prove the validity of the chain-reaction concept and then use the resulting nuclear reactor as a neutron source for further experimentation and data collection. Oddly, a separate uranium-enrichment task was spun off for Manfred von Ardenne, a German television pioneer, funded by the German Post Office.

Truth be known, Heisenberg was a brilliant theorist but not so good as an experimentalist, and his task involved building a nuclear reactor, which was heavy on the experimental side. He was grateful to be assigned Robert Dopel, professor of radiation physics at the University of Leipzig, to assist. It was Dopel and his wife, Klara, who decided that deuterium, the hydrogen isotope in “heavy water,” would be the ideal neutron moderator in a reactor using natural uranium. The construction of the first reactor, the L-I uranmaschine, was completed in August 1940. It was far subcritical, but it did accomplish neutron multiplication, producing more neutrons than were being injected from an external source, and it indicated that they were moving in the right direction. It would have to be rebuilt, larger, using heavy water, which was a precious material available sealed in 20-milliliter vials.

The Manhattan Project was doing basically the same thing in 1941, with a slightly different approach. Deuterium was indeed a fine neutron-moderating material, but, unlike the Third Reich, the United States had not captured a heavy-water-production plant in Norway. Instead, chemically pure synthetic graphite was used, delivered by the ton from Union Carbide. Enrico Fermi, a refugee nuclear scientist from Italy, headed the project, starting with a small pile of uranium and graphite in the corner of a lab at Columbia University. It was subcritical, but it multiplied the neutrons from a source. They were also going in the right direction, but they were one year behind the Germans.

By June 23, 1942, Heisenberg and Dopel had constructed L-IV, a bigger, more sophisticated version of their reactor in a dedicated laboratory building at the University of Leipzig. A large, circular pool of water was sunk into the middle of the floor in the lab. At the bottom was a frame, made of steel girders bolted together. Held off the bottom by the frame was a hollow sphere, one meter in diameter, of cast aluminum, three quarters submerged in the water. A flange around the circumference of the sphere was holding the upper and lower hemispheres together using 22 bolts. Four lifting lugs were cast into the flange with steel cables attached to a hoist above, and a long chimney emerged from the top, bolted to a flange on the upper hemisphere. On the inside surface of the sphere was a layer of uranium metal held in place by another, smaller flanged aluminum sphere. The inner space was filled with heavy water surrounding a still smaller sphere having another layer of uranium inside. A last aluminum sphere at the very center was filled with heavy water, and the chimney extended down through

the center of it. Four neutron counters were arrayed on the top hemisphere.39

The plan was to lower a fixed neutron source consisting of a mixture of radium and beryllium powders down the chimney to the center of the reactor. The neutrons would be slowed by the heavy water and hit the first hollow sphere of uranium from all interior directions. High-speed neutrons from the fission reactions in the uranium would fly into the second layer of heavy water, slow down, and impinge on the outer layer of uranium, causing a chain reaction and sending a portion of the resulting neutron burst back through the heavy water and into the inner uranium shell. The water immersion in the pool was supposed to keep the assembly from melting when criticality was achieved. They could not have been overly optimistic, as they had no particular plan for what to do if the thing sprang to life as a supercritical reactor, with the heat exponentially increasing. The sphere was sealed up tightly, with a gasket separating the two halves, because the metallic uranium would react chemically with any water leaking in, jerking the oxygen right out of the H2O.

That morning, Dopel had noticed something odd about L-IV. Bubbles were coming out of the sphere and bursting on the surface of the water in the pool. They had been experimenting with it since June 3, and it had seemed complacent, even dull and unresponsive, but now it looked angry. As he stood and tried to figure out what was wrong, the bubbles stopped. Nothing to be concerned about. Dopel struck a match over the last bubble as it surfaced, and it popped with a bang. Yep. The gas leaking out was hydrogen, or it could be deuterium. Somehow, water was getting to the uranium.

After lunch, Dopel and Paschen, the lab mechanic, winched the thing out of the water and started to loosen the bolts. A gasket must have failed and it would require replacement. As soon as the seal broke, the sphere made a sudden hiss. A vacuum had developed inside, and air was rushing in. They stood frozen for a second. It was quiet, then suddenly flames started shooting out around the flange, followed by molten uranium, scattering all over the lab. Dopel doused it with water as Paschen tried to re-tighten the bolts, and the flames seemed to subside.

Heisenberg was summoned. He did not know exactly how to handle this situation. A nuclear reactor had never caught fire before. He ordered the ball to be lowered into the pool. At least that would cut off the oxygen and keep it cool. Nothing burns, he thought, under water. He left it to Dopel and went to the adjacent building to hold forth at his weekly nuclear physics seminar.

At about 6:00 Dopel barged in, saying “You must come at once!” Heisenberg spun around to upbraid him for interrupting, but he saw a look of cold terror in his face. “You’ve got to come look at the thing!”

They hastened to the lab, and Dopel pointed down into the central pool. Steam was rising from the sphere. It looked as if it were… expanding? It gave a little shudder. Both scientists spun in unison and lunged for the door. The L-IV exploded with a roar, sending flaming uranium against the 20-foot ceiling and setting the building on fire. For two days it burned, with no amount of effort able to extinguish the burning remnants of the reactor, and it finally settled down into a gurgling swamp of radioactive debris.

Although the project was supposed to be a secret, the explosion was not, and Heisenberg had to endure winks and hearty congratulations from associates on his success with his atomic bomb. By the time the story had leaked across the ocean to the United States, it had grown considerably. An entire room full of German scientists had perished in a nuclear weapon test. For Heisenberg, it was no success at all. The metallic uranium in their pathetically subcritical assembly had simply caught fire. It was a setback. By December, the Americans had caught up with the Germans and passed them with a self-sustaining chain reaction. Security was so tight, the Germans did not even know they had been beaten. At the end of the war, their only accomplishment had been the world’s first nuclear reactor accident, caused by water leaking past an inadequate gasket.

The war ended with Emperor Hirohito’s “Jewel Voice” recorded radio announcement to the people of Japan on August 15, six days after the final atomic bombing run. It was over, and to the Manhattan Project the shock was deep. After this intense effort and all the frantic war research and industrial production in the United States, to have all activity stop suddenly was not exactly possible. There would have to be a short wind-down, before nuclear weapon development would rebound. The design of the plutonium implosion bomb was under constant modification and improvement, even as the Fat Man was dropping on Nagasaki, and reasons would be found to continue the work.

The model Y-1561 bomb, while successful, left much to be desired, and work was underway to increase its efficiency, as if a 20-kiloton blast was not big enough. The nuclear explosion occurred when a barely subcritical ball of plutonium metal, 3.62 inches in diameter, was crushed down to the size of a large marble by an explosive shock wave, turned inward. The nuclei of the plutonium were forced closer together than normal, and the chances of being hit with a flying neutron and fissioning were increased accordingly. The subcritical sphere became supercritical, at least three times over, and the uncontrolled chain reaction grew with devastating speed.

The little ball of plutonium was plated with 5.0 mils of nickel to prevent it from spontaneously catching fire as it was exposed to air. Around the fissile ball was assembled a “tamper” shell, 8.75 inches in diameter. Its purpose was to keep the plutonium ball together as long as possible as it was exploding to ensure that a maximum number of fissions could occur. With the fission rate doubling 90 times in a microsecond, the once-solid ball would become a superheated plasma, trying to expand from an inch in diameter to hundreds of feet in diameter as quickly as possible. Reasoning that even an atomic blast could not accelerate matter from rest instantly, the scientists decided to make the tamper shell of uranium metal, depleted of its fissile isotope. Aside from plutonium, it was the heaviest element available, and therefore it would provide the most inertial resistance to sudden expansion.

It was a touchy design. The plutonium component was built so close to criticality, the material

that would immediately surround it had to be chosen carefully.40 There was reason to believe that substituting tungsten carbide (WC) for the uranium in the tamper would up the yield by a kiloton. There was one question that could not be answered by theory: Exactly how much WC could surround the plutonium ball before the carbon atoms would reflect enough neutrons back into it to make it cross the line and go supercritical?

Improbable as it now seems, the answer to that question was to experiment standing over a plutonium bomb core with some bricks made of WC, stacking them up until the thing was on the verge of a runaway chain reaction. A plutonium ball on a workbench was not a plutonium ball crushed by an explosive shock wave, and there was no way to make it go off as a bomb, but it could be the world’s smallest, most simple nuclear fission reactor. Change its situation slightly, like by reflecting some stray, spontaneous neutrons back into it, and it could “go critical,” a condition in which it was producing exactly as many neutrons by fission as were being lost by leakage or absorption. “Supercriticality” could be slight, in which the energy-release rate increases slowly, or it could be great, depending on the degree with which it was perturbed.

“Tickling the dragon” involved the skill of making an eight-story house of cards. You had to be focused, alert, and stone sober.

Haroutune “Harry” Krikor Daghlian, Jr., was born in Waterbury, Connecticut, on May 4, 1921, to Haroutune and Margaret Daghlian, immigrated from Armenia. He earned a Bachelor of Science in physics at Purdue University. In the autumn of 1943, recruiters from the Manhattan Project found him working on the cyclotron at Purdue, trying to produce 10-MeV deuterons, and by 1944 he was working in Otto Frisch’s Critical Assembly Group at the Omega Site, Technical Area 2, at Los Alamos.

The Omega Site was stuck in a canyon, out of shrapnel range of the administrative and theoretical offices, so that only the technical class would be wiped out if an experiment were to go suddenly awry. By the end of the war, Daghlian had tickled the dragon so many times, he was at that very dangerous point where experience and confidence were so extreme, there was no need to be careful. Unlike the Oak Ridge workers, as a nuclear physicist he did not have ignorance as an excuse for not being terrified of his tasks.

All day on August 21, 1945, six days after Japan gave up, Daghlian worked on the WC loading for a 6.2-kilogram Mk-2 bomb core, standing over a low steel assembly table in the 49

Room at the Omega Site.41 There were workbenches on all four walls of the room, a desk for the SED security guard on the east wall exactly 12 feet away from the assembly table, and in the southeast corner was a special vault, made to store bomb cores isolated from each other

and from any radiation source.42 A stack of WC bricks of different sizes and shapes was piled on a rolling dolly to his left, and he would try various configurations against the ball of plutonium, always aware of the radiation counters ticking in the racks to his right. He had two fission chambers running numerical counters, each sounding a click in a loudspeaker every time a neutron hit, and a BF3 chamber indicating the neutron count rate visually with a strip-recording

milliammeter.— An experienced lab technician could tell easily if a criticality was imminent just by hearing the ticking sound become frantic, or at least mildly excited. In a specially machined brick, a 5-millicurie Ra-Be fixed neutron source sat against the ball, providing rogue neutrons to be multiplied by the plutonium and indicate its approach to criticality.

Daghlian was using rectangular WC bricks, 2.125 by 2.125 by 4.250 inches, and he found that the ball went critical when surrounded by five layers of bricks arranged as a cube with two bricks on top. He tried stacking the bricks differently, experimenting to find the minimum amount of WC that would cause the plutonium to take off. He logged out of the room at the end of the day after returning the sphere to the vault, scheduling another experiment with the bricks for the next day.

After dinner, he wandered over to the evening science lecture at theater no. 2, but something was bothering him about his last stack of bricks. He could not get it off his mind, and when the lecture broke up at 9:10, he went back to Room 49 in the canyon, arriving at 9:30. It was against regulations to perform a criticality experiment without an assistant, and it was certainly forbidden to do it after hours, but there was something he had to try or he could not sleep that night. Lights were on in the building.

Daghlian walked into the room, stood over the assembly bench for a second, then crossed the room to the plutonium vault to recover the ball. Sitting at the desk was SED guard Private

Robert J. Hemmerly, reading a newspaper. There had to be a guard on duty 24 hours a day in the room where bomb cores were. Daghlian looked nervous and apprehensive for some reason. Hemmerly said “Hi, Harry,” and returned to reading.

By 9:55 Daghlian had built his five-layer brick house around the bomb core, holding the brick that would seal the top in his left hand. Slowly he lowered it toward the pile, and the neutron counters started chattering madly. He had passed the critical line, barely, but the sudden radiation was startling. His left arm jerked upward to get the brick away from the pile. It slipped out of his hand.

Hemmerly was still sitting with his back to the assembly table, but he heard the rash of counts over the loudspeaker and then the clunk and the WC brick fell across the top of the plutonium ball, centered perfectly. The neutron detectors overloaded and the speakers went quiet as the wall in front of him lit up with a blue flash, and he twisted around.

Daghlian had caused a problem, and every instinct told him to immediately erase the problem. With his right hand he knocked the WC brick off the top of the assembly, glowing a pretty blue, and he noticed the tingling sensation of direct neuron excitation. He then stood there, arms limp

by his sides, coming to grips with what had just happened.44 He decided to dismantle the pile of bricks, and he calmly told Hemmerly what had occurred. Joan Hinton, a graduate student, happened to have just arrived at the Omega Site, and she drove the stunned scientist to the Los Alamos hospital as Hemmerly alerted Sgt. Starmer. Starmer was in the Omega Site office, which was separated from the 49 Room by a five-foot-thick shielding wall.

Daghlian’s right hand had endured a high dose of x-rays, gamma rays, and high-speed neutrons. There was no direct way to record the dose to his palm, used to brush aside the WC brick, but it was probably 20,000 to 40,000 rem. His left hand took a hit of 5,000 to 15,000 rem

as the brick hit the pile. His body absorbed about 590 rem.45

The first symptom of Daghlian’s radiation exposure observed at the hospital was the swelling and numbness in his right hand. Unrelenting nausea started 90 minutes after the accident, and continued for two days with a break only for prolonged hiccups. After 36 hours, a small blister appeared on his ring finger. Shortly after, the circulatory system in his hand collapsed and it turned blue, beginning with the nail beds. The blistering spread to the palm and then the back of the hand, and the hand essentially died. He was given opiates and ice packs in an attempt to control the pain.

After two days, he was feeling better and he was hungry. His arms, face, and body were turning red and skin was starting to come off, but he ate well and seemed to be improving. On the tenth day, the severe nausea returned, and he was no longer able to keep anything down. He started losing weight. He was given a blood transfusion, large doses of penicillin, vitamin B1, and quinidine sulfate. No treatment was reversing the condition. After 25 days, he slipped into a coma. He died at 4:30 P. M. on Saturday, September 15, 1945. His obituary in the New York Times said that he had perished from chemical burns. Harry Daghlian was the first person to die accidentally of acute radiation poisoning. It was history’s first mini-disaster involving nuclear fission out of control. The bomb core, not in its assigned role, had inadvertently become an unshielded nuclear reactor, suddenly achieving supercriticality and with no automatic shutdown system in place. There was nothing that could have been done medically to save his life.

The other victim, Private Hemmerly, had been exposed to the same radiation burst, but from a distance of 12 feet. He was confined to a bed for two days, with his only complaint that he felt tired. His blood samples showed increased leukocytes, but this condition was only temporary, and he was released after three days and returned to active duty. He went on to father two more children, and he died at the age of 62, showing no medical evidence that he had ever been exposed to a naked nuclear reactor. The difference between him and Daghlian was apparently the distance to the radiation source. In informed retrospect, if Daghlian had recoiled, jumping back from the assembly table when he dropped the brick instead of bending over to brush it off the pile, he would have survived. If he had been standing on the south side of the table instead of the north side, as was the case with Heisenberg and Dopel, he could have been out the door in three desperate bounds, with Hemmerly right behind him.

But, what would have happened to the supercritical plutonium ball? After a few seconds of power increase, the immediate temperature rise would have shut it down as the sphere expanded in the heat. The supercritical condition in a metal reactor of this size is so sensitive to perturbation, just a slight increase in the distances among plutonium nuclei is sufficient to stop the fissions. It would have then sat there with the heat diffusing slowly to the surface of the ball and radiating out into the room. As soon as it had reached room temperature, it would again become supercritical, and the cycle would start again, hosing the room once more with

radiation.46 After a few cycles, the movable WC bricks would be nudged to the sides by the expanding ball enough to no longer encourage another supercritical excursion, and the assembly would be stable but dangerous. A technician would enter the room behind a lead shield and dismantle the pile using a 20-foot metal pole, and Daghlian would have never been allowed again in the 49 Room.

This shocking event should have been a strong lesson learned, with measures implemented immediately to prevent its further occurrence. But, it wasn’t. Louis Alexander Slotin, an expert at assembling bomb-core experiments, was one of three investigators who submitted the accident report on August 26, 1945, five days after the Daghlian incident.

Slotin was born in 1910 to Jewish refugees who had fled the pogroms of Russia to make a life in Manitoba, Canada. He grew up on the north end of Winnipeg in a tight cluster of Eastern European immigrants, and he proved to be academically exceptional. He entered the University of Manitoba at age 16, earning a Bachelor of Science degree in 1932 and a Master of Science a year later, both in geology. Further study at King’s College London led to a Ph. D. in chemistry in 1936 and a wealth of dubious exploits. Later in life he would claim to have test-flown the first jet plane developed in England, despite lacking a pilot’s license. He captivated those listening with tales of having volunteered for service in the Spanish Civil War just for the thrill of it,

although there was some confusion as to which side he was on.47 At King’s he won the college’s amateur bantamweight boxing championship. His first job out of school was testing rechargeable batteries for the Great Southern Railways in Dublin, Ireland.

Back home in 1937, Slotin was turned down for a position with Canada’s National Research Council. He wangled a job as a research associate at the University of Chicago, where he worked on a cyclotron under construction in the Old Power Plant building. The pay was pitiful, but with help from his father to buy food he stayed on for a few years, using the new particle accelerator to make carbon isotopes for biological studies. It was claimed that he was present at Enrico “The Pope” Fermi’s CP-1 reactor startup in 1942, but nobody remembered him being there. He was caught in the sweep of the Manhattan Project draft and wound up at the Clinton Works in Oak Ridge.

At Oak Ridge he gained a reputation as someone who would step over the safety line and take chances that should not be taken. One Friday afternoon, young Louis wanted the X-10 graphite reactor shut down so that he could make adjustments to his experiment at the bottom of the fuel pool. It was a tank of water under the floor at the back of the reactor where hot, very radioactive fuel was dumped to cool off. The head of health physics, Karl Z. Morgan, nixed the idea. The pile could not possibly be shut down. It was being used as a pilot plant for the plutonium production reactors being built at Hanford, and the thing had to run 24/7, balls to the wall. Every few days, new fuel was pushed into the front face of the reactor, and the burned-up fuel would fall into the pool. The bottom had to be heavily contaminated by now.

When Morgan returned to work the following Monday, he discovered that Slotin had stripped down to his shorts, dived into the pool, and made his adjustments. Morgan was appalled. Slotin was reassigned to Los Alamos, where daring was better appreciated, in December 1944. He quickly earned respect for a natural ability to assemble the complicated implosion bomb without excessive worrying and hand-wringing. He expertly put together the bomb core for the Trinity test in New Mexico in July 1945. His unofficial title was Chief Armorer of the United States. The only reason he was absent on Tinian Island when the Fat Man was assembled was his lack of U. S. citizenship.

Slotin was shocked and saddened when Daghlian, his assistant and fellow dragon tickler, died in the criticality accident, and he spent days at his bedside in the hospital. This tragedy, however, did not affect his supreme confidence. He brushed aside advice that he should automate the critical assembly experiments, even when the very wise Fermi warned him that he wouldn’t last a year if he kept doing that experiment. The central problem pointed out by Daghlian’s death was approaching criticality from the top, where gravity could accidentally complete the operation. It would make more sense to assemble from the bottom. If anything was dropped, it would fall away from the plutonium sphere instead of into it. Slotin discounted the advice as an unnecessary complication.

The next atomic bomb explosion was to be a test in the middle of the Pacific Ocean at Bikini Atoll, designed to demonstrate that a navy flotilla could survive a nuclear attack and proving that the water-borne armaments had not been made obsolete by this recent innovation. The date for the Able shot in Operation Crossroads was set for July 1, 1946. The implosion bomb was under constant improvement, and the WC tamper had been replaced by a beryllium tamper. It was machined into a pair of concentric shells, 9.0 and 13.0 inches in diameter, and split into hemispheres to fit around the plutonium bomb core. The beryllium would act as a secondary neutron source during the explosion, hopefully increasing the number of fissions as the core destructed. A hole was bored into the top hemisphere so that the “initiator” modulated neutron source could be inserted into the core without dismantling the entire bomb. The criticality experiment for this revised tamper design was moved to a new building in Pajarito Canyon, and it would be performed using the same ball of delta-phase plutonium that had killed Daghlian.

On May 21, 1946, Slotin was training his replacement, Alvin C. Graves, who had a Ph. D. in physics from the University of Chicago. Slotin had grown weary of the bomb work, and was planning to bail out and go work in biochemistry back east. This would be his last bomb core.

It was about 3:15 in the afternoon. The experiment was set up on the low assembly bench, with the bomb set up near the edge and the 5 millicurie Ra-Be neutron source placed a few

inches in front of it.— Radiation detectors of several types were set up on and near the bench and warmed up, giving continuous recordings and audible clicks. There were seven men in the room, which was unusual for a criticality experiment, but this one was informal and was not scheduled. Two men had been working on initiator tests on a bench on the east side of the room, and the sensitivity of the required radiation counts had delayed them several times as the background counts were perturbed by tests outside the building. Slotin’s demo for Graves would also interrupt them, but it would be interesting to see him do the now famously dangerous criticality test. The SED guard was present, as were two other scientists, and they were all fascinated by watching the skilled Armorer at work. Three were standing directly in front of the bench. The room was brightly lit with overhead fluorescents and low sunlight through the windows.

The formal test called for wooden spacers to hold the top nine-inch tamper hemisphere off the bottom hemisphere, and it was to be gradually lowered onto the core by changing out the spacers, one at a time, with smaller ones until the assembly was very close to criticality. Both the 13-inch and the 9-inch tamper hemispheres were installed only on the bottom of the assembly. The tamper pieces would then be sent back to the shop to have some metal removed, and the test would be done over until the assembled bomb was stable and very near the critical condition.

Slotin discarded the spacers and used a big-bladed screwdriver instead. With the blade under the lip of the tamper, he could lever it up and down, impressing Graves and his audience by making the neutron count rate zoom in and out on the loudspeaker. Graves was close behind him, looking over Slotin’s right shoulder. Slotin’s left thumb was through the access hole on top of the tamper, with his fingers on the curved side, adding to the downward tension of the movable tamper-half. He pulled the screwdriver handle up, increasing the angle between the bottom hemisphere and the straight blade, with the top hemisphere riding up, increasing the gap and making the neutron count rate fall precipitously. At an angle of 45 degrees, the screwdriver arrangement became precarious, as the side thrust, pushing the screwdriver outward from the gap, equaled the downward thrust holding the screwdriver down. Ever upward Slotin angled the tool. Beyond 45 degrees, the outward thrust overcame the downward thrust, and the screwdriver suddenly escaped the gap.

Bang.

The top tamper fell squarely on the bomb assembly, and prompt criticality was achieved

instantly.49 The blue flash lit up the entire room, as the neutron counters, ticking merrily along, suddenly jammed and went quiet. Slotin, on pure instinct, jerked the tamper off the assembly and dropped it on the floor. He could feel the tingling in his left hand and he could taste the radiation on his tongue. It had happened again, and there was no ignorance at work here. Familiarity to the point of nonchalance had just claimed another victim.

Slotin had a body dose of 2,100 rem of mixed radiation, or twice the dose of guaranteed lethality, and he died the same way Daghlian had, only faster, nine days later. The same radiation pulse hit Alvin Graves, standing an inch from Slotin, but he was partly shielded by the

Armorer’s body. He stayed in the hospital a few days and was released. The other men in the room showed minimal effects from the incident.

The Crossroads tests went on as planned, with the Able shot using the bomb core that had killed two scientists. The bomb, dropped from a B-29, was affectionately named Gilda, and had a picture of Rita Hayworth painted on the side. The yield was 23 kilotons, or 3 kilotons more than the device dropped on Nagasaki a year earlier with a uranium tamper. The target flotilla consisted of 95 vessels of all types, from a captured Japanese battleship to a floating

drydock.— All were sunk, lost, damaged beyond repair, or made dangerously radioactive except one, the U. S. submarine Dentuna, which was refurbished and returned briefly to naval service. The ships were manned by 57 guinea pigs, 109 mice, 146 pigs, 176 goats, and 3,030 white mice. Some lived through the air blast and the radiation pulse, with the most famous survivor being Pig 311, who was found swimming in Bikini lagoon after it stopped raining battleship fragments. He lived out his life at the Smithsonian Zoological Park in Washington, D. C., on a government pension.

There would never be another manual bomb assembly experiment, anywhere or any time. There was still a need to test-assemble the core parts to find unwanted critical conditions, and even an application of a chain-reacting naked plutonium core, to produce the specific radiation spectrum of an atomic bomb explosion. All further work was done at a distance of a quarter of a mile, using remote controls, television cameras, and a quick shutdown capability. The practice of bringing very small, bare metal reactors to the power-production point was still an extremely ticklish, sensitive action, but at least nobody could get hurt. That was the intent, at least, but fissionable materials always seemed capable of finding a flaw in the best intentions. All the

remote-controlled assemblies in the United States were named “Godiva.”—

The first Godiva to go out of control was on February 1, 1951. The bomb designers at Los Alamos were working on the Mk-8, a light-weight bomb similar to the one used on Hiroshima, and two sections of highly enriched uranium, the “target” and the “projectile,” were suspended by poles in a water tank to see how close they had to be in a moderating medium to reach criticality. The poles ran on motorized tracks, so the distance between the two uranium pieces could be controlled. There were three ways to scram the experiment: the target could be withdrawn using a pneumatic cylinder on its pole, the water could be drained out of the tank, and a cadmium sheet could be dropped between the target and the projectile. When the assembly barely reached criticality, all three scrams were put into action.

The cadmium screen, absorbing neutrons with a vengeance, dropped. The water started draining, and the target started pulling out of the tank as quickly as possible. Just then, the TV camera whited out from steam coming out the top of the tank, and the neutron detectors jammed. If they had had a color camera, they would have seen the water vapor turn blue. To the amazement of the experiment crew, the thing had gone prompt critical.

This was not a life-threatening situation, because the experimenters were far removed from the incident, but still it was another criticality accident, and it once again rammed home the fact that a metal-on-metal reactor was tricky beyond theory. All the minds at Los Alamos had yet to outfox it. The recognition of this flaw led to further design work and improvements. There was not going to be another Slotin incident at a national lab.

Analysis and re-creation of the accident found the problem. As the target was jerked out of the tank, the back-wash from the swirling water had banged the two pieces together, flexing the poles that were holding them and overcoming the reaction-dampening effect of the cadmium sheet. Who would have predicted it? Further criticality mistakes occurred at Los Alamos on

April 18, 1952, February 3, 1954, February 12, 1957, and June 17, 1960.— Causes were one too many uranium disks added to a stack, a piece of neutron-moderating polyethylene left too close to Godiva, and pieces that were supposed to slide past one another not doing so. There were criticality accidents with Godivas at Oak Ridge on November 10, 1961, Lawrence Livermore on March 26, 1963, White Sands Missile Range on May 28, 1965, and the Aberdeen

Proving Ground on September 6, 1968.—

It is interesting that all of these Godivas jumping out of control were loaded with metallic uranium or uranium alloy. Not one criticality accident using plutonium was logged, despite the fact that very few bomb designs used uranium cores. The safety measures were laudable, as not one worker was exposed to any radiation, and machine destruction was never something

that could not be fixed in three days.54 Meanwhile, our Soviet counterparts were doing the same thing, experimentally assembling fissile components to find that exactly subcritical configuration that would be stable yet triggerable in a bomb. Their experiences would prove to be even more dramatic than ours.

The old town of Sarov in Nizhny Novgorod Oblast in eastern Russia disappeared off all maps in 1946 when it became the home of the All-Union Scientific Research Institute of Experimental Physics, or the Soviet equivalent of Los Alamos, New Mexico. It was renamed Arzamas-75 to confuse, indicating that it was 75 kilometers down the road from the town of Arzamas, which it was not. The name was changed to the more accurate Arzamas-16 when it was realized that Arzamas wasn’t on a map either.

In Building B were two “vertical split tables,” which were very well designed machines that would conduct critical assemblies by remote control. The top half of a bomb was supported on a steel table, and the bottom half was pushed slowly into position from underneath using a motorized jack-screw. Not being ones to assign cute monikers, Soviet scientists named them FKBN and MSKS.

The building was well designed for safety, but it was not perfect. The FKBN was located in a concrete room with seven-foot-thick walls and a vault door. There was no straight crack around the door where radiation could escape, and the control room was in an adjacent space. The MSKS was in a long chamber with rails on the floor, across the corridor from the FKBN control room. It was shielded with five feet of concrete, and the split table and a separate neutron source trolley could roll back and forth on rails to vary the mutual distance. The MSKS control room was across the corridor from the source trolley, and it was set up better than the FKBN control room, in that it had a back door. Dash out of the FKBN control room, and you were right in front of the door to the MSKS. The rules were that before you could set up an experiment on the MSKS, you had to first prove that it would not run away on the heavily shielded FKBN.

On March 11, 1963, the chief of operations and the head engineer were setting up an approach-to-criticality experiment on the MSKS without bothering to try it first on the FKBN. The assembly was a boosted implosion device with a delta-phase plutonium core, 135mm in diameter. The core was surrounded by a tamper shell, 350mm in diameter, made of lithium deuteride. A fixed neutron source was installed in the middle of the core, instead of the initiator source, throwing about a million neutrons per second into the assembly. The neutron detectors were turned off, so there was no automatic scram system working, and the two supervisors were trying to adjust the lift mechanism on the fully loaded split table, bumping it up and down. It was sticking. On the last try, the two halves clapped shut.

The room lit up with a blue flash. There was no audible count-rate or anything else to indicate that something was wrong, but the two experienced nukes had an excellent idea of what had happened. The ball of plutonium had gone prompt critical, which can happen when two organic neutron-moderating reflectors are kneeling at the thing, jockeying the controls. The two lunged for the door and scrambled down the hall, turning left into the control room. The chief hit the down button for the lift.

They did not die. With doses of 370 and 550 rem, they were just under the lethal limit, although they were definitely injured and spent months in the hospital. One lived another 26 years, and the other was still alive in 1999. They were guilty of gross violations of the MSKS operating procedures, even though one of them had written the manual.

Another interesting mistake was made at Arzamas-16 on June 17, 1999. A highly respected experienced scientist wanted to recreate an experimental assembly he had made back in 1972. He first made the Daghlian error, working alone and not having completed the paperwork, in a new building made to house an improved split table, the FKBN-2M.

This device was shielded by nine feet of concrete on all four sides and the ceiling, with the control room outside the south wall. The lower works would move up and down with a hydraulic lift, but the fixed upper portion of the assembly could be rolled back on rails to give you room to build up the bottom half of your bomb experiment. A sensitive automatic scram would gravity- drop the bottom half quickly if it went supercritical.

The experimenter opened his old logbook, looked up the dimensions of his original assembly, and started stacking components on the lift, with the top half rolled out of the way. It was an unusual bomb, built using an imploding uranium-235 core with a copper tamper. His second error was that in his log he had written the wrong diameter of the reflector. It had been 205mm, but he had written 265mm. He scrounged up the right nested copper bowls to build up his

reflector. “Like a matryoshka doll,” he thought.55 He built up the bottom reflector using four bowls, then dropped in the uranium ball with a hundred-thousand-neutrons-per-second fixed source inside. He wanted to build up two layers of reflector on top, then roll the top assembly over it, retire to the control room, and slowly assemble his experiment into a critical mass. He dropped the first layer of copper bowl over the core.

Oops. The assembly went prompt supercritical, instantly spiking at over 100 million watts. A blue flash, of course, over-lit the room. Obviously, there was too much reflector under the core. The assembly scrammed, dropping to the floor, but there was nothing to drop away from. All the reactivity was present on the lower half of the assembly, and the top of the machine had been moved out of the way. The experimenter, knowing what he had done, ran out of the room, closed the vault behind him, told two guys in the control room what had happened, and died of severe radiation poisoning two days later. His radiation dose from neutrons alone was several

times the lethal level.56

The assembly heated up to 865°C, expanded, and settled down to a stable power level of 480 watts, fissioning away for six and a half days until the emergency crew was able to position a vacuum gripper on it and pull off the copper tamper-piece on top.

In 1957 an additional atomic city was built in the Chelyabinsk Oblast in the Urals district of Southern Russia. It was named Chelyabinsk-70, home of the All-Russian Scientific Research Center of Technical Physics, or the VNIITF. After the end of the Cold War it was reassigned the name Snezhinsk, which was easier to pronounce. The extensive research facilities included an FKBN vertical split table, just like the one at Arzamas-16.

On April 5, 1968, two very knowledgeable, experienced criticality specialists were experimenting with a special reactor setup on the split table. The goal was to make a tiny reactor to be used in pulse-mode to investigate the effects of the radiation spike from a nuclear weapon detonation. All day they had tried different configurations. At the center of the reactor was a hollow sphere of 90% enriched uranium, or 43.0 kilograms of uranium-235 in a 47.7 kilogram ball, 91.5mm in diameter with a 55mm cavity inside. The reflector halves were natural uranium, making a hollow sphere 200mm in diameter. In the last configuration they tried, the uranium sphere had nothing but air in the center. They had lowered the top reflector half onto the ball using an overhead electrical winch, then retired to the control room, closing the shielding vault door, and slowly drove the lower reflector up toward the assembly until it went critical. Satisfied with the result, they then drove the bottom reflector down until the assembly

went subcritical, which was with the southern hemisphere 30mm below the stop.57

It was late and after hours. The health physicist and the control room operator had gone home. The two specialists had tickets to the theater, and they were in a hurry to leave, but there was one last thing they wanted to try. Not bothering to turn on the criticality alarm, they used the winch to lift off the top reflector half, removed the top core half, and inserted a polyethylene ball in the empty cavity. For some inexplicable reason, these two experts did not expect a hydrogen-containing moderator at the center of the reactor to change anything, but they just wanted to make sure. One operated the control box for the overhead winch while the other steadied the heavy, 308-kilogram hemisphere as it came down on the core-ball at 100mm per second.

Blue flash! With his hands on the reflector, one felt a shock, as if the thing had been struck with a mallet. Both were hit in the face by the wave of heat as the system’s reactivity flew past the prompt critical level. When the power level hit one kilowatt and rising, the scram activated, and the bottom of the assembly fell away, but it was too late for the specialists. Before they left the control room the lower reflector should have been lowered to the bottom stop, but it was kept at the level that was barely subcritical for the assembly with a hollow center. The one with his hands on the uranium absorbed between 2,000 and 4,000 rem, and he died three days later in the Bio-Physics Institute in Moscow. The man who was holding the winch control only received something between 500 and 1,000 rem, and he managed to cling to life for 54 days.

These two men suffered from the same supreme confidence in what they were doing that had killed Louis Slotin. They had violated many rules, including the most important one: Every unmeasured system is assumed to be critical. It is the same as finding a pistol sitting on a table. Assume that it is cocked and loaded.

The nuclear age had arrived with a pronounced bang, and by 1947 two experts had died trying to achieve zero-power criticality in the simplest possible reactor configurations. It had become obvious that an extraordinary level of caution would be needed to do anything practical with this new discovery, this new, novel, and dangerous way to heat the old cave. Be careful, or the innocent-looking ball of metal could pin you to the wall like a mule with a long-festering grudge. And a radioactive one at that.

Nuclear reactor systems were about to get a lot more complicated, with more moving parts, pumps, valves, controls, indicators, and data recorders, and a great deal of plumbing. The heart of the system, the reactor core, was going to be covered up by layers of safety-ensuring machinery and made abstract by the interpretive instrumentation; but we must never forget that at the center of it all, danger still lurks. Remain alert, capable of terror, and never so familiar with the routine that you are certain that nothing could happen.

25 It was reasoned that the occupant of this palace, Emperor Hirohito, would be instrumental in issuing an expected surrender. However, on July 20, 1945 a single B-29 strategic bomber dropped a replica of the Fat Man atomic bomb containing 6,300 pounds of high explosive (baratol) from 30,000 feet with the bomb-sight cross-hairs on the geometric center of the imperial residence. It was a clean miss. In the weeks before Fat Man was dropped on Nagasaki, 49 of these “pumpkin bombs” were dropped on Japan, killing an estimated 400 people and injuring 1,200, as practice for the A-bomb mission. With the random aiming uncertainties of high-altitude bombing, the only way to ensure that the Emperor would not be hit was to aim directly at him.

26 The city was unmolested by aerial bombs, but it was not exactly in pre-war condition. That summer before the A-bomb was dropped, school children, aged 11 to 14 years, had been mobilized into a demolition force, tasked with tearing down all the houses or businesses on certain streets. As had been witnessed in other cities many times during this last year, a few B-29s carrying incendiary bombs could wipe out a Japanese city just by starting fires. Japanese houses were notoriously flimsy and made of flammable materials, and multiple ignition points would quickly overwhelm any firefighting effort. Entire streets leveled to the ground were to act as firebreaks, preventing the spread of fire over the entire city by creating zones of nothing burnable.

27 Once the heavy bombing campaigns started on Japan in 1944, it was standard procedure to drop leaflets warning the population to evacuate. This was good military practice, because it was possible to partially empty out a city and send the residents fleeing to the hills. The war-material factories would thereby lose the workforce, and vital production would come to a stop. Given vague warnings of future bombing raids, 120,000 people of the 350,000 population evacuated Hiroshima prior to the A-bomb attack.

28 Tokyo Rose was a generic name given to any of about a dozen English-speaking women on the NHK propaganda channel, transmitting popular American music, radio skits, and carefully slanted battle news. Listening between the lines, the average soldier could gauge how badly it was going for the Japanese forces by the daily news from Rose. This particular announcer was possibly Iva Toguri D’Aquino, an American citizen who was caught in Japan at the beginning of the war. Convicted of treason in 1949, Toguri was pardoned by President Gerald Ford in 1977.

29 The only record I can find of this action is in a book written by team member Harlow W. Russ, Project Alberta: The Preparation of Atomic Bombs for Use in World War II. Los Alamos, NM: Exceptional Books, 1984. I won’t say that Mr. Russ is a stickler for details, but he wrote down the contents of every meal he had on the way to Tinian Island, and his 1945 New Mexico fishing license is faithfully copied into the appendices.

30 This one-megaton bomb is a theoretical device used by Samuel Glasstone in his definitive work, The Effects of Nuclear Weapons (1957), in his detailed analysis of an atomic bomb explosion. The actual bomb that destroyed Hiroshima was smaller, 16 kilotons, but the effects scale down only slightly.

31 The airburst tactic did two things: it maximized the radius of destruction, and it minimized the resulting radioactive fallout. The explosions kicked up a lot of dust, but the only radioactive material to be spread off-site was the bomb itself, which was about 9,700 pounds of metal. The bomb debris consisted of fuel that failed to fission, fission products, and various metals in the structure of the device, a portion of which were neutron-activated to radioactivity in the explosion.

32 Atomic bomb trivia: Stenciled in black on the bright orange nose of the Fat Man bomb were two things: a profile of a fat man with a capital F at his back, and the cryptic inscription “JANCFU.” It meant “joint army navy and civilian fuck-up.” The assembly team had been unable to use the heat-tempered armor plates for the bomb’s airframe. The plates had been warped in the process of hardening them, and in desperation they resorted to using the mild steel plates left over from the pumpkin series of practice bombs. Once they got it all together, they realized that one of the safety plug sockets had been wired wrong. With no time to take the thing all apart and re-wire the socket, they modified the safety plug to match the error, so this bomb was not completely built-to-prints.

33 The first written account of the John Hendrix story I can find is in Robinson, George O., The Oak Ridge Story; the saga of a people who share in history. Kingsport, TN: Southern Publishers, 1950, published some eight years after the supposed prophecy came true. There is some question as to when Hendrix died. This book says 1903, and others say 1915, but this volume includes photos of his once home and his gravestone. He did what the Voice told him to do and found a good place to sleep in the woods, fitfully, for 40 nights. During many of those nights, it rained on him.

34 K-25, using the gaseous diffusion process, was used to “enrich” uranium for bombs, research reactors, submarines, and power plants for the next 40 years. The other two methods for uranium enrichment, the thermo-columns at site S-50 and the electromagnetic calutrons at site Y-12, were torn down quickly after the war ended. Two large diffusion plants were built in Paducah, Kentucky and Portsmouth, Ohio, to increase production during the Cold War, and these were copies of the Oak Ridge facilities. However, K-25 did not add to the highly enriched uranium used in the Little Boy bomb dropped on Hiroshima. The diffusion process was slow, and the uranium fed in at the mouth of the process did not have time to reach the end-product stage by the time the war ended. Using the highly inefficient Y-12 process, by August 1945 we had just enough uranium-235 for exactly one bomb.

35 Actually uranium oxide dissolves in water, and not pure uranium metal. Another possibility is to have natural, out-of-the-ground uranium oxide dissolved in heavy water, or deuterium oxide. Using ordinary water, the plain hydrogen in it can occasionally absorb a neutron, and this is a neutron that misses the opportunity to trigger a fission. Deuterium, which is hydrogen that already has that neutron in the nucleus, doesn’t absorb neutrons, and for that reason heavy water encourages fission more than ordinary water. You could stack up bottles of plain uranium in heavy water and cause a meltdown. The dynamics of fission are that sensitive.

36 This problem is only hypothetical. During the war, there was never enough uranium-235 existing at Oak Ridge to make a purely metallic, highly enriched critical mass. As soon as a piece of it the size of a silver dollar accumulated, it was sent off to Los Alamos, where every scientist knew of the potential hazard of collecting the metal in one place.

37 A blatant exaggeration, but you get the point. As will be chronicled in a later chapter, this accident has happened on many occasions. When the contents of the drum go supercritical, the water boils vigorously. Just the boiling action changes the configuration enough to throw the reactor into subcriticality and the reaction stops. The radiation burst of an uncontrolled approach to criticality in an unshielded assembly is deadly to any nearby organism.

38 Well, maybe a few. On June 6, 1945, the exact critical mass of a uranium-235 bomb core was still unknown, and an experiment using 35.4 kg of 79.2% enriched uranium metal was devised. Blocks of the uranium were built into a pseudosphere surrounded by paraffin. The assembly was placed in a large tank of water. As the tank was being filled, the thing went unexpectedly critical, and there was no way to scram it. Someone lunged for the drain valve, which was 15 feet away and finally brought it under control. Three scientists received “significant” radiation exposure, but they seemed unscathed.

39 This incident is fairly well known, but there is some confusion about the exact configuration of the reactor. The uranium is often described as being in powdered form, which makes no sense. If it were powdered, the uranium metal would have reverted to uranium oxide before the sphere was loaded, and metallic uranium was thought to be essential. It was most likely uranium metal formed into marbles, so that they could be packed between aluminum shells. To machine hollow hemispheres of uranium would have been unnecessarily difficult. An alternate, more plausible configuration of L-IV is in a drawing captured by the Alsos Mission in 1945. It shows flat plates of alternating uranium metal and deuterated paraffin stacked inside the aluminum sphere. With ten plates of uranium (551 kilograms) and ten plates of paraffin, only the top hemisphere was filled. The plan was to load two plates at a time while monitoring the neutron multiplication, stopping when criticality was achieved.

40 Georgia Tech physics professor Nesbit Kendrick, my faithful source of atomic bomb stories, told me about the problem of inserting the plutonium “peach-pit” into the center of an Mk-4. You had to hold it connected to the end of a T-wrench and carefully insert it through a hole that was opened up in the high explosives (HE) that surrounded it. The explosives were complex organic compounds containing hydrogen, which is a very effective neutron moderator, and as the pit passed through the hole, slow neutrons would bounce back into it and it would go supercritical on a slow period! One did not linger in the midst of the HE, lest the fission neutrons boiling off the plutonium sphere burn the skin off the hand gripping the wrench handle.

41 The information in this account comes from the classified “REPORT OF ACCIDENT OF AUGUST 21, 1945 AT OMEGA SITE.” The report was unclassified on August 28, 1979, and publicly released on January 28, 1986.

42 SED means Special Engineer Detachment.

43 The “fission chamber” is an ion-chamber tube lined with uranium-235. If a neutron wanders into it, a fission will likely occur in the uranium, and this ionizing event causes the gas in the tube to conduct electricity which is countable as one neutron interception. The BF3 chamber is not quite as sensitive. The ion chamber is filled with boron trifluoride gas, and if a slow neutron is captured by the boron, the resulting radioactive decay of the activated boron will also ionize the gas and register as an encounter with a neutron.

44 A characteristic that all criticality accidents seem to have in common is the blue flash. It is caused by the sudden blast of radiation from the uncontrolled chain reaction ionizing nitrogen gas in the air and causing it to glow a characteristic color. In this first case, the glow was about two inches deep around the box made of WC bricks.

45 Roentgen Equivalent Man. The rem is an obsolete measure of radiation dose, taking into account the unique sensitivities of the average human body Doses in the range of 1,000 rem are usually fatal. The current measure of dose is the sievert. To convert rem to sieverts, divide the value in rems by 100.

46 The “supercritical” condition is necessary for this to be a disaster. Any reactor can be exactly critical, conducting self-sustaining fission, while generating no detectable power. The only way to bring an operating reactor up to a useful power-level is to temporarily add some reactivity, making it slightly supercritical. When the power level is achieved, the reactor is leveled off at exactly critical. To lower the power level, the reactor is rendered slightly subcritical on a temporary basis.

47 Slotin’s brother, Sam, in a later interview revealed that Louis had gone on a short walking tour in northern Spain and had participated in the revolution only in spirit.

48 Declassified documents differ on the type of neutron source used. One says it was a radium-beryllium source, and one says it was plutonium — beryllium. Usually not mentioned was an extremely active 30 curie polonium-beryllium source, three months old, located about seven feet east — northeast of the assembly table. These seem minor points, but one strives for as much accuracy as possible.

49 “Prompt criticality” is an important term. It means that a state of at least break-even chain reaction was reached using only promptly available neutrons. There was no need to wait for the delayed fission neutrons, which could take seconds, to get a load sufficient to declare the assembly critical. The additional reactivity needed to go from delayed to prompt criticality is exactly one dollar. The practice of expressing reactivity in dollars and cents, still in use today, was coined by Dr. Louis A. Slotin.

50 The Japanese battleship was the Nagato, carefully placed in the array so that it would be certain to sink. It had been the command ship from which the Pearl Harbor attack was directed back in 1941, and to sink it with an A-bomb was symbolic. It was a well-built ship, and two nuclear devices failed to send it to the bottom. The target point was the battleship Nevada, a survivor of Pearl Harbor. It was painted red so that the bombardier could see it (not likely in warfare), but they missed it by 710 yards, putting the bomb on top of a lowly transport ship, the Gilliam.

51 Not really At the Los Alamos Lab there were also the Topsy and the Jezebel assemblies. These specialized devices may have been better designed, as no unplanned criticalities were ever reported for them. The French were conducting similar experiments at about the same time, first at Saclay with the PROSERPINE and ALECTO assemblies and then after 1961 at the Valduc Research Centre using the CASTOR and POLLUX machines (rig B and rig D). No accidents were recorded.

52 The uranium assembly built in 1952 was named “Jemima.” The Mk-8 uranium bomb was already deployed by then. Jemima was probably the W-9 280mm artillery shell, being handed over to the Army that month.

53 Lockheed Nuclear Products received the go-ahead to build a Godiva II on an aluminum railcar for use at the Georgia Nuclear Aircraft Laboratory in 1957. This plutonium “pulse reactor” was supposed to simulate a nuclear weapon explosion below the nuclear-powered bomber as it flew away after a drop. Would the radiation pulse confuse the engine instruments and cause a scram in the aircraft? I find no record of its use nor accident reports.

54 There was also a “mini-Godiva” for portable use by weaponeers. An aluminum Halliburton case was filled top and bottom with paraffin, with cutouts shaped to fit the target-piece for a uranium assembly weapon. A BF3 neutron detector and a fixed neutron source were also embedded in the paraffin, with a cable connection for the counter electronics in another Halliburton. The target was made of little uranium discs that would screw together into a cylinder. In the field it could be shimmed to the proper level of activity by adding or subtracting discs. The specialist would lay the cylinder in the paraffin nest, close the case, and push a button on the neutron counter. After counting neutron hits for a minute, the activity level of the target was evaluated

using the results.

55 Perhaps. I actually don’t know what he was thinking, but the metaphor was too thick not to use it.

56 Technically he absorbed 4,500 rad of neutron radiation and 350 rad gamma rays. The rad is an obsolete measurement that does not take into account the “Q,” or the radiation quality factor and how it affects humans. Assume a Q of one, and he got a body dose of at least 4,850 rem. It was probably closer to 40,000 rem or 400 sieverts, which would drop an elephant.

57 If you are amazed by some of the detailed information available concerning Soviet nuclear work, read an example of glasnost in the Proceedings of ICNC’95, Vol. 1, pp. 4.44-4.47, “Criticality Measurements at VNIITF Review,” V. A. Teryokhin, V. V. Pereshogin, and Yu. A. Sokolov.

Chapter 3