The Trinity Paradox (18 page)

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 must 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.

“Are we ready to begin?” he asked.

The others looked to Hahn, who handed his notebook to someone else. “Yes. First we must add our neutron source. Spontaneous neutrons should be sufficient, but this will make sure the reaction commences.” He raised an eyebrow. “We are tossing our first marble into the room, Professor Esau.”

Esau nodded.

“Then we will drop the remaining uranium oxide rods into the pile. This should bring us to criticality. The reaction will be self-sustaining.”

Esau folded his arms across his chest. “You may proceed.” But Hahn had already gone to the equipment piled along the walls, opening a small wooden case lined inside with lead foil. He withdrew a thin glass cylinder.

“This neutron source contains radon gas and beryllium powder. You may find it ironic that the Nazis confiscated it from the laboratories of Frederic and Irene Joliot-Curie in Paris.”

Diebner laughed. He had taken many of the Joliot-Curie notes from their laboratories, claiming the discoveries as his own. No one else said anything.

Hahn climbed the ladder to the top half of the graphite pile rising from the pit in the floor. Suspending the glass tube from a thin chain, he dangled it and let the neutron source slide down into the central hole. The clicking of the counters increased. Hahn looked over his shoulder at them. “That is as we expected. Everything is now in place.”

Esau felt nervousness chewing inside of him. “Fine. We are already behind the Americans. No use wasting time. Let’s see if the reactor works.” He listened to the counters rattling and thought of Hahn’s mousetraps.

Paul Harteck spoke up. “Would everyone please step behind the shielding wall? The leaded glass observation windows should protect you.” No one needed to be reminded twice.

“Perhaps we should proceed an inch at a time,” Hahn said, coming around behind the wall. “We will gain more information that way.”

Esau crowded up so he could see through the narrow window. “We can repeat the experiment later if you require such niceties. For now, we must see if all of us have a future here! If we do not show success with this, certain people will be very upset.” He turned to von Weizsacker. “Lower the uranium oxide.”

Von Weizsacker looked to Hahn, then Diebner, as if searching for someone to counteract Esau’s orders, but no one would speak out loud. Some of the assistants edged toward the door. Von Weizsacker released the catch on the chain, letting the six rods of uranium oxide fall into place inside the pile, bringing the pile beyond its critical limit.

The neutron counters went wild, rattling and roaring. Any attempt to keep track of individual counts failed in an instant. Esau could see no apparent difference from watching the pile.

“The reaction is self-sustaining!” Hahn cried.

Paul Harteck stood on the opposite side of the room behind another barricade, staring down at his counter. He had to shout over the noise of the cheering and the neutron counters. “It is still climbing.”

The pile looked unchanged, but the neutron counters insisted that something wondrous kept happening at the core. They had succeeded! With only minimal information, they had reproduced the triumph of Enrico Fermi a few months earlier. Perhaps the German program would not remain so far behind at all. He couldn’t wait to send a telegram to Reichminister Speer.