business; not when a slip might result in the atomic detonation of two and
a half tons of uranium.
He tried to visualize what that would mean, and failed. He had been told
that uranium was potentially forty million times as explosive as TNT. The
figure was meaningless that way. He thought of it, instead, as a hundred
million tons of high explosive, two hundred million aircraft bombs as big
as the biggest ever used. It still did not mean anything. He had once seen
such a bomb dropped, when he had been serving as a temperament analyst for
army aircraft pilots. The bomb had left a hole big enough to hide an
apartment house. He could not imagine the explosion of a thousand such
bombs, much, much less a hundred million of them.
Perhaps these atomic engineers could. Perhaps, with their greater
mathematical ability and closer comprehension of what actually went on
inside the nuclear fission chamber — the “bomb” — they had some vivid
glimpse of the mind-shattering horror locked up beyond that shield. If so,
ho wonder they tended to blow up —
He sighed. Erickson looked up from 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.
The accelerator’s snout disappeared in the shield between them and the
bomb, where it fed a steady stream of terrifically speeded up subatomic
bullets to the beryllium target located within the bomb 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 proportions 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 chain reaction.
But these chain-reactions were comparatively unimportant; 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 isotope 235 may be split by bombarding it with neutrons
from an outside source, 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 the eruption of
Krakatoa to popgun 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.
But a self-perpetuating sequence of nuclear splitting, just under the level
of complete explosion, was necessary to the operation of the power 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 output of power from the system should exceed the power
input in useful proportion it was imperative that each atom split by a
neutron from the beryllium target should cause the splitting of many more.
It was equally imperative that this chain of reactions should always tend
to dampen, to die out. It must not build up, or the entire mass would
explode within a time interval too short to be measured by any means
whatsoever.
Nor would there be anyone left to measure it.
The atomic engineer on duty at the bomb could control this reaction by
means of the “trigger,” a term the engineers used to include the linear
resonant accelerator, the beryllium target, and the adjacent controls,