Today, we ask about Germany and the atom bomb in
WW-II. The University of Houston's College of
Engineering presents this series about the machines
that make our civilization run, and the people
whose ingenuity created them.
Physicist Jonothan Logan
tells a strange tale that begins in 1945, soon
after Germany surrendered. Fifteen of Germany's
greatest physicists have been taken to an English
country house and asked to write an account of
German science during the war.
Suddenly, a radio announcement: The BBC says an
atomic bomb has fallen on Hiroshima with a blast
equal to 2000 ten-ton bombs.
Werner Heisenberg, of Heisenberg Uncertainty
Principle fame, is there. He doesn't know the
English have hidden microphones in the room. He
blurts out that such a bomb would be impossible. No
one had enough uranium to do the job. Some
dilettante in America, who knows very little about
it, has bluffed them, he grumbles.
The transcripts of those conversations were only
declassified in 1992. As we listen in, a
half-century later, we learn the real reason why
Germany never produced an atom bomb.
The idea of an atomic bomb had been born seven
years before -- in February, 1939. That's when
Lisa Meitner published a
paper with her nephew Otto Frisch explaining the
release of energy by the fission of uranium. Seven
months later Germany invaded Poland and full war
began. Meanwhile, both Meitner and Frisch got out
of Germany.
Meitner wanted nothing to do with bombs. She wanted
to create peaceful nuclear power. But in 1940,
Frisch wrote the English military to tell them it'd
take only one kilogram of uranium 235 to make a
bomb. U-235 is a hard-to-separate isotope that
makes up less than one percent of natural uranium.
Frisch underestimated how much of it we'd need, but
only by a factor of ten. Heisenberg also made the
calculation and got 13,000 kilograms. The huge
difference in estimates has to do with the way
chain reactions work:
A neutron is so tiny and fast moving that it
travels a long distance in uranium before it
chances to hit an atom and knock more neutrons
loose. If it has to travel, say, a full meter, you
need a huge chunk of U-235 to get a chain reaction.
If it only has to travel, say, one centimeter, then
a small block of U-235 will do the trick.
Heisenberg, brilliant theoretician, overestimated
the path of travel. Experimentalists Meitner and
Frisch did far better; and Frisch's note sent
America on the way to building a bomb. Heisenberg's
estimate so discouraged the German High Command
that they never did undertake serious
bomb-building.
Back in that English country house, Heisenberg
heard about the second bomb over Nagasaki. So he
quickly figured out how his calculation should've
gone in the first place. Then he told the English
he could've built a bomb all along, but he and his
colleagues had been anti-Nazi. They'd kept Germany
from bomb building and steered her into a slow
program of nuclear power development.
That was the story for the next forty-seven years.
Then we finally opened those hidden microphone
records -- and history changed.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.
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