Digital Fortress

Susan knew Jabba was right. Because the number line was infinite, one could always look a little farther and find another prime number. Between zero and a million, there were over 70,000 choices. It all depended on how large a prime Tankado decided to use. The bigger it was, the harder it was to guess.

"It’ll be huge." Jabba groaned. "Whatever prime Tankado chose is sure to be a monster."

A call went up from the rear of the room. "Two-minute warning!"

Jabba gazed up at the VR in defeat. The final shield was starting to crumble. Technicians were rushing everywhere.

Something in Susan told her they were close. "We can do this!" she declared, taking control. "Of all the differences between uranium and plutonium, I bet only one can be represented as a prime number! That’s our final clue. The number we’re looking for is prime!"

Jabba eyed the uranium/plutonium chart on the monitor and threw up his arms. "There must be a hundred entries here! There’s no way we can subtract them all and check for primes."

"A lot of the entries are nonnumeric," Susan encouraged. "We can ignore them. Uranium’s natural, plutonium’s man-made. Uranium uses a gun barrel detonator, plutonium uses implosion. They’re not numbers, so they’re irrelevant!"

"Do it," Fontaine ordered. On the VR, the final wall was eggshell thin.

Jabba mopped his brow. "All right, here goes nothing. Start subtracting. I’ll take the top quarter. Susan, you’ve got the middle. Everybody else split up the rest. We’re looking for a prime difference."

Within seconds, it was clear they’d never make it. The numbers were enormous, and in many cases the units didn’t match up.

"It’s apples and goddamn oranges," Jabba said. "We’ve got gamma rays against electromagnetic pulse. Fissionable against unfissionable. Some is pure. Some is percentage. It’s a mess!"

"It’s got to be here," Susan said firmly. "We’ve got to think. There’s some difference between plutonium and uranium that we’re missing! Something simple!"

"Ah… guys?" Soshi said. She’d created a second document window and was perusing the rest of the Outlaw Labs document.

"What is it?" Fontaine demanded. "Find something?"

"Um, sort of." She sounded uneasy. "You know how I told you the Nagasaki bomb was a plutonium bomb?"

"Yeah," they all replied in unison.

"Well…" Soshi took a deep breath. "Looks like I made a mistake."

"What!" Jabba choked. "We’ve been looking for the wrong thing?"

Soshi pointed to the screen. They huddled around and read the text: …the common misconception that the Nagasaki bomb was a plutonium bomb. In fact, the device employed uranium, like its sister bomb in Hiroshima.

"But-" Susan gasped. "If both elements were uranium, how are we supposed to find the difference between the two?"

"Maybe Tankado made a mistake," Fontaine ventured. "Maybe he didn’t know the bombs were the same."

"No." Susan sighed. "He was a cripple because of those bombs. He’d know the facts cold."

Chapter 126

"One minute!"

Jabba eyed the VR. "PEM authorization’s going fast. Last line of defense. And there’s a crowd at the door."

"Focus!" Fontaine commanded.

Soshi sat in front of the Web browser and read aloud. …Nagasaki bomb did not use plutonium but rather an artificially manufactured, neutron-saturated isotope of uranium 238."

"Damn!" Brinkerhoff swore. "Both bombs used uranium. The elements responsible for Hiroshima and Nagasaki were both uranium. There is no difference!"

"We’re dead," Midge moaned.

"Wait," Susan said. "Read that last part again!"

Soshi repeated the text. "…artificially manufactured, neutron-saturated isotope of uranium 238."

"238?" Susan exclaimed. "Didn’t we just see something that said Hiroshima’s bomb used some other isotope of uranium?"

They all exchanged puzzled glances. Soshi frantically scrolled backward and found the spot. "Yes! It says here that the Hiroshima bomb used a different isotope of uranium!"

Midge gasped in amazement. "They’re both uranium-but they’re different kinds!"

"Both uranium?" Jabba muscled in and stared at the terminal. "Apples and apples! Perfect!"

"How are the two isotopes different?" Fontaine demanded. "It’s got to be something basic."

Soshi scrolled through the document. "Hold on… looking… okay…"

"Forty-five seconds!" a voice called out.

Susan looked up. The final shield was almost invisible now.

"Here it is!" Soshi exclaimed.

"Read it!" Jabba was sweating. "What’s the difference! There must be some difference between the two!"

"Yes!" Soshi pointed to her monitor. "Look!"

They all read the text: …two bombs employed two different fuels… precisely identical chemical characteristics. No ordinary chemical extraction can separate the two isotopes. They are, with the exception of minute differences in weight, perfectly identical.

"Atomic weight!" Jabba said, excitedly. "That’s it! The only difference is their weights! That’s the key! Give me their weights! We’ll subtract them!"

"Hold on," Soshi said, scrolling ahead. "Almost there! Yes!" Everyone scanned the text. …difference in weight very slight… …gaseous diffusion to separate them… …10,032498X10?134 as compared to 19,39484X10?23.** "There they are!" Jabba screamed. "That’s it! Those are the weights!"

"Thirty seconds!"

"Go," Fontaine whispered. "Subtract them. Quickly."

Jabba palmed his calculator and started entering numbers.

"What’s the asterisk?" Susan demanded. "There’s an asterisk after the figures!"

Jabba ignored her. He was already working his calculator keys furiously.

"Careful!" Soshi urged. "We need an exact figure."

"The asterisk," Susan repeated. "There’s a footnote."

Soshi clicked to the bottom of the paragraph.

Susan read the asterisked footnote. She went white. "Oh… dear God."

Jabba looked up. "What?"

They all leaned in, and there was a communal sigh of defeat. The tiny footnote read: **12% margin of error. Published figures vary from lab to lab.

Chapter 127

There was a sudden and reverent silence among the group on the podium. It was as if they were watching an eclipse or volcanic eruption-an incredible chain of events over which they had no control. Time seemed to slow to a crawl.

"We’re losing it!" a technician cried. "Tie-ins! All lines!"

On the far-left screen, David and Agents Smith and Coliander stared blankly into their camera. On the VR, the final fire wall was only a sliver. A mass of blackness surrounded it, hundreds of lines waiting to tie in. To the right of that was Tankado. The stilted clips of his final moments ran by in an endless loop. The look of desperation-fingers stretched outward, the ring glistening in the sun.

Susan watched the clip as it went in and out of focus. She stared at Tankado’s eyes-they seemed filled with regret. He never wanted it to go this far, she told herself. He wanted to save us. And yet, over and over, Tankado held his fingers outward, forcing the ring in front of people’s eyes. He was trying to speak but could not. He just kept thrusting his fingers forward.

In Seville, Becker’s mind still turned it over and over. He mumbled to himself, "What did they say those two isotopes were? U238 and U…?" He sighed heavily-it didn’t matter. He was a language teacher, not a physicist.