Heinlein, Robert A – Expanded Universe

want, doe?”

“Harper is relieved from watch. You take over as engineer-of-the-watch. Send

for the standby engineer.”

“Very well.” His voice and manner were phlegmatic, as he accepted the

situation without comment. The atomic engineer whom he had just relieved glanced

from one to the other, then carefully replaced the wrench in its rack.

“Just as you say, Doctor Silard, but send for your relief, too. I shall

demand an immediate hearing!” Harper swept indignantly out, his lead-sheathed boots

clumping on the floorplates.

Doctor Silard waited unhappily for the ensuing twenty minutes until his own

relief arrived. Perhaps he had been hasty. Maybe he was wrong in thinking that

Harper had at last broken under the strain of tending the most dangerous machine in

the world-the atomic breeder plant. But if he had made a mistake, it had to be on

the safe side-slips must not happen in this business; not when a slip might result

in atomic detonation of nearly ten tons of uranium-238, U-235, and plutonium.

He tried to visualize what that would mean, and failed. He had ‘been told

that uranium was potentially twenty million times as explosive as T.N.T. The figure

was meaningless that way. He thought of the pile instead as a hundred million tons

of high explosive, or as a thousand Hiroshimas. It still did not mean anything. He

had once seen an A-bomb dropped, when he had been serving as a temperament analyst

for the Air Forces. He could not imagine the explosion of a thousand such bombs;

his. brain balked. Perhaps these atomic engineers could. Perhaps, with their greater

mathematical ability and closer comprehension of what actually went on inside the

nuclear fission chamber, they had some vivid glimpse of the mind-shattering horror

locked up beyond that shield. If so, no wonder they tended to blow up- He sighed.

Erickson looked away from the controls of the linear resonant accelerator on which

he had been making some adjustment.

“What’s the trouble, doc?”

“Nothing. I’m sorry I had to relieve Harper.”

Silard could feel the shrewd glance of the big Scandinavian. “Not getting

the jitters yourself, are you, doc? Sometimes you squirrel-sleuths blow up, too-”

“Me? I don’t think so. I’m scared of that thing in there-I’d be crazy if I

weren’t.”

“So am I,” Erickson told him soberly, and went back to his work at the

controls of the accelerator. The accelerator proper lay beyond another shielding

barrier; its snout disappeared in the final shield between it and the pile and fed a

steady stream of terrifically speeded up sub-atomic bullets to the beryllium target

located within the pile itself. The tortured beryllium yielded up neutrons, which

shot out in all directions through the uranium mass. Some of these neutrons struck

uranium atoms squarely on their nuclei and split them in two. The fragments were new

elements, barium, xenon, rubidium-depending on the portions in which each atom

split. The new elements were usually unstable isotopes and broke down into a, dozen

more elements by radioactive disintegration in a progressive reaction.

But these second transmutations were comparatively safe; it was the original

splitting of the uranium nucleus, with the release of the awe-inspiring energy that

bound it together-an incredible two hundred million electron volts-that was

important-and perilous.

For, while uranium was used to breed other fuels by bombarding it with

neutrons, the splitting itself gives up more neutrons which in turn may land in

other uranium nuclei and split them. If conditions are favorable to a progressively

increasing reaction of this sort, it may get out of hand, build up in an

unmeasurable fraction of a micro-second into a complete atomic explosion-an

explosion which would dwarf an atom bomb to pop-gun size; an explosion so far beyond

all human experience as to be as completely incomprehensible as the idea of personal

death. It could be feared, but not understood.

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But a self-perpetuating sequence of nuclear splitting, just wider the level

of complete explosion, was necessary to the operation of the breeder plant. To split

the first uranium nucleus by bombarding it with neutrons from the beryllium target

took more power than the death of the atom gave up. In order that the breeder pile