“Professor Heisenberg had not given any final answer to my question whether a successful nuclear fission could be kept under control with absolute certainty… Hitler was plainly not delighted with the possibility that the earth under his rule might be transformed into a glowing star.”
—Albert Speer, Nazi Minister of Armaments
The truck pulled up with the last shipment of graphite blocks. Professor Abraham Esau stood in the doorway of the Virus House laboratory, watching it stop in front of the wrong building. Two other technicians ran out in the cold autumn drizzle to direct the driver toward the main bunker. The armed guards on the truck raised their rifles and aimed at the men hurrying toward them; the technicians stopped just in time, waving their arms.
In a way, Esau found it ludicrous, squadrons of guards flanking a graphite truck. Why would any outside saboteur want to steal a shipment of carbon! He’d had an extremely difficult time convincing the German graphite manufacturers—who had never seen more than a minimal war demand for their product—of his need for absolute priority. When orders on his “Plenipotentiary” stationery proved ineffective, Esau had obtained a direct letter from Reich-minister Speer. Finally, things got done properly.
Esau had used Speer’s authorization letter several more times, first to insist on delivery within weeks rather than months, then to force the companies to manufacture graphite with a process that used petroleum coke rather than mineral coke. The new process proved much messier for the manufacturer and cut production in half—but the mineral process always contaminated graphite with boron, the neutron absorber that had ruined Walther Bothe’s initial measurements.
Esau hated it when people, through their own laziness, tried to deceive him. “It cannot be done!” the manufacturers said. But Esau was aware of the petroleum process because some British factories produced ultra-pure graphite for specialized use in electrode tips. He and Graham Fox had required those elements for their experimental work back in Cambridge.
“It will be done,” he muttered to himself outside the Virus House, then pulled up the collar on his jacket and hurried over to the truck.
The driver and the guards worked with Virus House technicians to unload the crates and take them into the bunker building. Esau watched them work. The drizzle could have ruined some of the shipment, but someone had thought to wrap the boxes in waxed paper, which kept everything dry. Other technicians emerged from the bunker, their faces looking comically black from carbon dust.
Esau waited by the truck cab in the shadow of the rain until the workers had finished unloading. “I am Professor Esau. Do you have a receipt for me?” he asked the guard captain.
“Yes, sir.” The guard fumbled inside his wet leather jacket and withdrew a folded set of papers.
Esau took them and removed a fountain pen from his pocket, looking for a flat surface on which to write and finally settling on the wet side of the truck. He scrawled his initials and then carefully printed his full title below. “Now we have everything,” he said to himself.
“Heil Hitler!” the guard said, tucking the papers back inside his pocket.
Esau responded, then walked back toward the bunker. He didn’t listen as the motorcycles started and the truck ground its gears, backing up in the mud and gravel where Heisenberg had been shot two months before.
Inside the bunker, Esau approached the researchers and their assistants. The interior walls had been knocked down by scientists with sledgehammers, leaving only support beams at regular intervals throughout the room. Near the door, Esau stepped around crates filled with ultra-pure graphite bricks, all cut to size for the appropriate lattice spacing.
Much of the floor had been torn up in the center; long wooden planks with protruding nails lay piled against one wall. Construction workers had dug a large pit in the ground, lined it with concrete and then with plates of beryllium metal to reflect back neutrons that tried to spill out of the growing pile.
Down in the pit, three workers had placed a layer of carbon bricks along the bottom. Others passed more of the black, shiny blocks down in a fire-brigade line. Smashed fingers occurred regularly as the workers fumbled with the slippery graphite.
Dr. Kurt Diebner, Esau’s former rival, was one of the men down in the pit doing menial work. Esau smiled, considering it good for the man to get his hands dirty. And dirty he certainly was—his face, his balding head, his thick black glasses, his hands, his neck—everything was covered with shiny black dust that stuck to his sweat, clung to his pores.
All of the scientists from the scattered groups of German nuclear research had been summoned here to share offices in the Virus House. Esau himself had moved away from his precious office in the Federal Building downtown. Now, in the unimpressive barracks, he occupied Werner Heisenberg’s former office. He did that intentionally for its psychological effect, to emphasize who was in charge and what he could do if the other researchers displeased him.
He had assigned Diebner to share an office with Manfred von Ardenne, the man who had convinced the Reichpost Ministry to fund his private nuclear research. Von Ardenne was a pleasant, quiet, but brilliant researcher— probably the only one who could tolerate Diebner’s excessive ego for any length of time.
Diebner and Paul Harteck—the two dynamos behind the Göttingen research group—stuck together in their clique, working on their solo research and keeping their secrets. Or at least they had tried to—Esau had put a stop to it immediately. No longer were they petty factions competing against each other. They were competing against the Americans, who, according to Graham Fox’s message, had already succeeded beyond anything the Germans had accomplished.
The floor in the bunker felt slick from the fine black dust that clung to everything. While the graphite bricks had been cut to proper size, the workers used modified woodworking tools to cut notches for the uranium cubes. Each of the lattice holes had to be customized, because Esau was using all the uranium and uranium oxide he had cobbled together from the scattered experiments of the other research teams.
Uranium metal cubes would be scattered at six-inch intervals in the graphite material, but Carl-Friedrich von Weizsacker’s calculations had shown that this would not be enough to make the reaction self-sustaining. Within the growing pile, they would add a circular array of uranium oxide in long tubes. In the center of this they would drop the neutron source that should trigger the whole reaction.
Von Weizsacker climbed out of the pit, saw Esau standing there and walked over to him. “I now recall the papers I discussed with you earlier, Professor Esau, the last open reports about the American nuclear research.” He wiped his blackened hands on his blackened coveralls.
“They were published in Physical Review, in English. I remember reading them on the underground railway in Berlin. I believe I received a few suspicious glances when people saw me poring over an American periodical. This was in June 1940, I believe. Some scientists had reported using Lawrence’s cyclotron at Berkeley to create element 93 by bombarding uranium. But element 93 is unstable and undergoes beta decay, turning into element 94. That is the one we want. Element 94 is fissionable, and stable, and chemically different from uranium. We can make your weapon. If we can get this pile working.”
Esau could sense von Weizsacker dancing around the real issue. He felt impatient. By focusing on the optimistic good news, von Weizsacker implied that he also had something bad to say. “I know all that. So what is the problem?”
“Well, it will be very difficult for us to make sense out of our measurements from this pile we are building,” he said with no other preamble. Specks of graphite blackened von Weizsacker’s teeth, but the smudges could not disguise his boyish features, his statue-perfect Aryan appearance.
“We are mixing the sizes of the uranium cubes, adding the uranium oxide to the metal, changing the spacing. Too many variables in everything. Normally, we would build successive piles, each one simple and straightforward, with conditions we could understand and attempt to p
redict. With successive attempts we can add new twists and see how that affects the readings. We will never be able to understand this reaction. It is too complicated.”
Esau met the younger man’s eyes. He sensed that von Weizsacker had been chosen as a delegate from the other scientists. He noticed that the work had stopped. He kept his voice firm.
“I am not interested in understanding it at this moment. I am interested in demonstrating that it will work! Nuclear physics fascinates me as well, but have you not been listening to the radio broadcasts? The constant bombing of Frankfurt. The American General Eisenhower announcing the unconditional surrender of Italians, and then Italy declaring war on Germany!
“I must deal with the Reichminister of Armaments, who in turn must deal with the Führer. Everyone wants a useful weapon now. Understanding can come later.” Esau turned to go back to his office, but stopped. “When will the pile be ready?”
Von Weizsacker shrugged. “They are still hooking up the counters, and we will need to take measurements at successive stages of the assembly to see how far we must go to achieve criticality.”
Esau kept staring at him, waiting for an answer.
The younger man stopped, thought a minute, then nodded. “Late this evening, I would guess.”
“Good. I will be in my office.”
The man who had discovered nuclear fission, Dr. Otto Hahn, had been chosen the de facto leader of the Kaiser-Wilhelm group. Esau fostered this impression, since he respected Hahn. And Hahn seemed more interested in his physics than in using his authority, which was fine with Esau.
The great physicist, though, treated Abraham Esau like a schoolboy to be lectured. Esau’s own grasp of nuclear physics, though considerable, did not compare with the researchers working under him. He forced himself not to act too impatient when Hahn began to teach him about the pile being constructed in the bunker. Hahn ignored the fact that Esau himself had passed along the key bit of information about graphite.
Otto Hahn himself insisted on “clarifying” it to Esau, making sure that the Plenipotentiary understood the enormity of the event about to take place. Hahn stood in Heisenberg’s old office as Esau dutifully watched the great man pace. Hahn began to talk in his quiet voice.
“We know nothing about what the Americans have done, but we can conjecture how to repeat their experiment. In principle at least.” Esau noticed the stubble on Harm’s cheeks. His moustache stood out, and his eyes looked big and sad, bloodshot from too little sleep. “This goes far beyond the tiny laboratory exercises that I did with Herr Strassman and Dr. Lise Meitner—”
“You need not credit a Jew for your discovery, Dr. Hahn,” Esau interrupted, straightening in his seat.
Hahn halted his pacing, raised his bushy eyebrows and turned to Esau. “Lise did much of the work. She had the idea first. She understood long before I did—” He stopped himself, but Esau already knew what Hahn thought. Rumors even said that he had helped Lise Meitner escape to Sweden, but Hahn had never said this aloud.
Esau didn’t want to push him. He needed Hahn’s mind, his ideas, to make a self-sustaining chain reaction. “No matter. We are worried about physical principles now, not political ones.”
Hahn nodded curtly. “So we are. We know that the uranium nucleus can fission, and that it is the scarce 235 isotope that fissions due to slow neutrons. Niels Bohr pointed that out.”
Esau let his eyes fall closed for just a moment. Bohr, the half-Jew. It seemed they permeated nuclear physics.
“But now we cannot be satisfied with causing merely a fission or two just to prove that it can be done. We must make one fission cause another, and another, and another, so that the reaction continues of its own. Then perhaps it can be useful, such as making a uranium burner to produce power. That was one of Heisenberg’s ideas.”
“We wish to make a weapon, Dr. Hahn. Not a furnace.”
“Both work on the same principle. Listen.” He held up one finger, a thick finger, with blackened pores and nails from handling the carbon blocks. It would take weeks to wash everything off. Even after a thorough shower, the pores of the skin exuded graphite dust within another hour.
“In your mind, Herr Esau, picture a mousetrap with a marble balanced just above the spring.” He stepped back and gestured to the empty floor. “Now picture this floor covered with such mousetraps, each one loaded with a marble, each one ready to snap the instant an appropriate signal is received.”
Involuntarily, Esau leaned over and looked at the bare wooden planks of the floor. Hahn glanced around as if suddenly remembering where he was, then he lowered his eyes and fixed his face into a scowl. “Professor Heisenberg was very good at these thought experiments too.”
Esau said nothing. He tapped his fingertips together and waited for Hahn to continue.
“Now, I will stand outside this room full of mousetraps…” Hahn stepped back, holding one hand up and keeping a gap between his fingers as if holding something. “I have a marble in my grasp. I toss it into the room.” He mimed the gesture.
“The marble in my hand is like a neutron that I send into our reactor. Each of our mousetraps, cocked and holding their marbles, is like a uranium nucleus waiting to fission.
“My marble strikes a mousetrap, setting it off. The spring snaps up, sending my initial marble and its own marble flying into the air. Each of those two marbles strikes another mousetrap, sending two new marbles into the air, plus the same two all over again. Now we have four marbles launched in different directions, heading to different targets. And it repeats again, and again, all in a few seconds! It is like a firestorm, yes? Suddenly the air is filled with flying marbles. The sounds of clacking and springing and snapping!
“This intense reaction will continue for only a moment until all the mousetraps have sprung. All the marbles fall to the floor. Do you see how much energy I have released by simply tossing one particle?” He snapped his black-stained fingers. “That is how your bomb will work, all in an instant.”
Hahn stepped back into the office. “But that is not how our first chain reaction must work. We cannot have everything used up in an instant. We need the reaction to continue in a much slower, controlled manner, because we are using the excess flying marbles to build our new element 94. How do we do this? How can we control such an inferno?
“Imagine perhaps the room filled with cocked mousetraps again, but most of them are not loaded with marbles. Only a few of them. The rest are bare. We must get the right amount of mousetraps loaded—the right amount of uranium-235 in the mixture—and we must also space the mousetraps at the appropriate distances from each other so our result is that on average each marble that strikes a mousetrap causes exactly one more marble to fly in the air. In this way the reaction will continue at a controllable rate for as long as we require it.”
Esau smiled. “Most elegant.”
“The universe is elegant,” Hahn answered, “but secretive. It is up to us to unravel these secrets. In times of war we must unravel them faster than we might like.”
“That is the right attitude, Dr. Hahn.” Esau smiled in a way that might have been considered patronizing.
Hahn stiffened. “Professor Esau, I have already invented one terrible weapon in my life. During the Great War, Fritz Haber and I were the first to consider using poison gas against the enemy. Phosgene, chlorine gas, mustard gas. We were the first. It was our idea. Fritz Haber’s wife was a chemist herself, the first woman ever to receive a degree from Breslau University. She despised her husband’s work. She called it an abomination of science.”
Hahn lowered his eyes, letting them sink deeper behind his bushy eyebrows. “Dr. Clara Haber committed suicide when her husband refused to stop his work on our ‘super weapon.’ “
Esau decided to show compassion in his voice. “I am sorry to hear that.”
“Fritz Haber told me that a scientist belongs to the world in times of peace, but to his country in times of war. So now it is a time of war, and once again I m
ust turn my work to the benefit of Germany. No matter what it does to the rest of the world.”
He stared at his fingers. “I like to consider myself a gentle man, but if you count all the victims of poison gas in the Great War, I already have the blood of over a million people on my hands.” He raised his eyes. “Please don’t treat me as if I am not aware of what we are doing here.”
He glared at Esau once, then left the office.
“It will go critical in the next few layers, Professor Esau.” Esau blinked, startled. He had fallen asleep with elbows sprawled on the wooden desktop. He glanced at von Weizsacker waiting by the door, then he looked at the clock. It was just past two in the morning. “I will be there shortly.” He blinked sleep away from his eyes.
A few moments later he ran along the gravel path to the bunker. Inside, naked bulbs flooded the pale walls and graphite-dusted floor, making it look like a bad black-and-white photograph. Two men continued to assemble the pile; the rest stood waiting behind the cinder-block observation wall that would shield them from stray radiation.
The pile had filled the deep pit. Graphite bricks and chunks of uranium stood in a blocky, somewhat spherical configuration. Neutron counters placed at various locations clicked from the presence of stray particles by the natural uranium decay. Otto Hahn and Paul Harteck stood beside opposite detectors, recording neutron counts as each layer was added to the pile.
Diebner climbed down from the pile. “That is the last layer, according to our calculations.” He kept his voice neutral. “If it doesn’t work now, we must begin again from scratch.”
Suspended above the pile from a chain on the ceiling, six tubes of uranium oxide hung partially inserted within the mound of black bricks. They would be the last pieces to enter the reacting pile. Von Weizsacker stood by a lever that would release a massive counterweight in case of an emergency; the weight would fall and yank out the uranium oxide rods, bringing the pile back to a subcritical state. As an added safety measure, Diebner and Harteck had mounted a drum filled with boric acid solution over the pile; in an extreme situation they could dump the solution into the pile, where the boron would swallow up all the free neutrons and smother the chain reaction. Esau winced at the drum’s precarious position. An accident could spill the boric acid into the graphite bricks, ruining the ultra-pure carbon that had been so difficult to obtain.
The Trinity Paradox Page 13