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Lawrence. Heard of them?”

“Yes.”

“Thought they were colleagues, partners, right?”

“I suppose so.”

“Wrong. They were rivals. See, we all knew the key was uranium, the world’s heaviest element. And we knew by 1941 that only the lighter isotope, 235, would create the chain reaction we needed. The trick was to separate the point seven percent of the 235 hiding somewhere in the mass of uranium-238.

“When America entered the war, we got a big leg up. After years of neglect, the brass wanted results yesterday. Same old story. So we tried every which way to separate those isotopes.

“Oppenheimer went for gas diffusion—reduce the uranium to a fluid and then a gas, uranium hexafluoride, poisonous and corrosive, difficult to work. The centrifuge came later, invented by an Austrian captured by the Russians and put to work at Sukhumi. Before the centrifuge, gas diffusion was slow and hard.

“Lawrence went for the other route—electromagnetic separation by particle acceleration. Know what that means?”

“I’m afraid not.”

“Basically, you speed the atoms up to a hell of a velocity, then use giant magnets to throw them into a curve. Two racing cars enter a curve at speed, a heavy car and a light car. Which one ends up on the outside track?”

“The heavy one,” said Martin.

“Right. That’s the principle. The calutrons depend on giant magnets about twenty feet across.

These”—he tapped the Frisbees in the photograph—“are the magnets. The layout is a replica of my old baby at Oak Ridge, Tennessee.”

“If they worked, why were they discontinued?” asked Martin.

“Speed,” said Lomax. “Oppenheimer won out. His way was faster. The calutrons were extremely slow and very expensive. After 1945, and even more when that Austrian was released by the Russians and came over here to show us his centrifuge invention, the calutron technology was abandoned. Declassified.

You can get all the details, and the plans, from the Library of Congress. That’s probably what the Iraqis have done.”

The two men sat in silence for several minutes.

“What you are saying,” suggested Martin, “is that Iraq decided to use Model-T Ford technology, and because everyone assumed they’d go for Grand Prix racers, no one noticed.”

“You got it, son. People forget—the old Model-T Ford may be old, but it worked . It got you there. It carried you from A to B. And it hardly ever broke down.”

“Dr. Lomax, the scientists my government and yours have been consulting know that Iraq has got one cascade of gas diffusion centrifuges working, and it has been for the past y

ear. Another one is about to come on stream, but probably is not operating yet. On that basis, they calculate Iraq cannot possibly have refined enough pure uranium—say, thirty-five kilograms—to have enough for a bomb.”

“Quite right,” nodded Lomax. “Need five years with one cascade, maybe more. Minimum three years with two cascades.”

“But supposing they’ve been using calutrons in tandem. If you were head of Iraq’s bomb program, how would you play it?”

“Not that way,” said the old physicist, and began to roll another cigarette. “Did they tell you, back in London, that you start with yellowcake, which is called zero-percent pure, and you have to refine it to ninety-three-percent pure to get bomb-grade quality?”

Martin thought of Dr. Hipwell, with his bonfire of a pipe, in a room under Whitehall saying just that.

“Yes, they did.”

“But they didn’t bother to say that purifying the stuff from zero to twenty takes up most of the time?

They didn’t say that as the stuff gets purer, the process gets faster?”

“No.”

“Well, it does. If I had calutrons and centrifuges, I wouldn’t use them in tandem. I’d use them in sequence. I’d run the base uranium through the calutrons to get it from zero to twenty, maybe twenty-five-percent pure; then use that as the feedstock for the new cascades.”