The Making of the A-bomb
Marcus Brüggen
Outline
• History of the atomic bomb
Discovery of Fission and its Properties
First Investigations of Atomic bomb
The Manhattan Project
Racing against Victory - the final year
Hiroshima and thereafter
• Nuclear Weapon Physics and Design
• Facts about Nuclear Weapons and Final Remarks
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The Trinity site today. The obelisk marks the spot of the explosion
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• Feb. 1932: James Chadwick demonstrates existence of neutron
(1935 Nobel Prize)
• 1933: Leo Szilard conceives the idea of a chain reaction
• Oct. 1934: Enrico Fermi - principle of neutron moderation
• Dec. 1938: Hahn and Strassmann: production of barium from
neutron irradiated uranium: evidence for fission
At this point: Unclear how self-sustaining chain-reaction could arise
Key uncertainties:
1) number of neutrons emitted / fission
2) cross-sections for fission and absorption
• Aug. 1939: Bohr & Wheeler: theoretical analysis of fission
U-235 more fissile than U-238. Undiscovered element
94-239 also very fissile.
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• Aug. 1939: Einstein/Szilard letter to FDR written
• Sep. 1939: Germany invades Poland, beginning WWII
• Feb. 1940: Research into isotope separation and fast fission
starts in the UK (Frisch, Peierls, MAUD committee)
• May 1940: Germany launches assaults on Western Europe
• Feb. 1941: Seaborg & Wahl discover plutonium
• Mar. 1941: x-section of U-235 is measured; Peierls calculates
critical mass as 18 pounds
• May 1941: Segre & Seaborg measure fission x-section of
plutonium: high value
• Sep. 1941: Churchill instigates development of atomic bomb
• Dec. 1941: Pearl Harbor
By early 1942 fission physics was hardly explored. Experimental
data was scarce and poor.
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Szilard and Einstein together after the War
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• Jul.1942: Oppenheimer assembles theory group in Berkeley
to study bomb design (Bethe, Teller, Bloch ...)
• Sep. 1942: Gen. Groves heads construction of Manhattan Project
• Dec. 1942:Fermi’s CP-1 pile in Chicago went critical
(thermal output = 0.5 W, k=1.00006)
• Apr.1943: Bethe head of theory group at Los Alamos
• Nov. 1943: Bohr, Frisch, Peierls, Chadwick, Fuchs move from
UK to US to assist in bomb project
At the end of 1944 feasibility of bomb still looks grim:
Bomb design exists for U-235, which was virtually impossible to
produce. Plutonium was about to begin but no bomb designs
existed.
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Robert Oppenheimer
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Hans Bethe
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Enrico Fermi
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• Dec. 1944: Large-scale plutonium production begins
• Jan. 1945: Y-12 in Oak Ridge:204 g of highly (80%) enriched
U/day (electromagnetic separation)
• Apr. 1945: 25 kg of U-235 and 6.5 kg of Pu-239 on hand
bomb seems feasible
Target Committee meets for the first time
• May 1945: Germany capitulates
• Jul. 1945: Gadget is detonated at Trinity test site in the first
atomic explosion in history. Explosive yield 20 kt,
vaporising steel tower.
• Jul. 1945: Truman discloses existence of bomb to Stalin
(who already knew about it)
Groves drafts directive for use of bomb. Target list:
Hiroshima, Kokura, Niigata, Nagasaki
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The D-reactor at Hanford
The Y-12 plant at Oak Ridge
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Sgt. Herbert Lehr delivering
the plutonium core (or more
probably half of it) for the
Gadget in its shock-mounted
carrying case to the assembly
room in the McDonald Ranch
farmhouse.
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The partially assembled Gadget.
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Oppenheimer and Groves
inspecting the remains of
the Trinity test tower
9 Sep. 1945
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The heat of the Trinity
explosion melted the
sandy soil around the
tower to form a glassy
crust known as
"trinitite".
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• Jul. 1945: Japanese reject Potsdam Declaration requiring
unconditional surrender
• Aug. 6 1945:”Little Boy” explodes over Hiroshima (U-235)
• Aug. 9 1945 “Fat Man” explodes over Nagasaki because
Kokura is covered by Haze. (Pu)
• Aug. 1945 Japan surrenders
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Blue print of Fat Man
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Fat Man bomb being prepared for loading on the B-29 Bock's Car
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Little Boy and Fat Man
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Hiroshima
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Edward Teller
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"Most did not know about this work. It was top secret. Among those
who knew, not all understood, and among those who understood, not
all had access to key decision-makers in Washington. Among those
who knew, and understood, and who had access, I was the only one
who stood up for it. Without that, it is certain the positive
information would never have reached the President. I did
something, and I'm glad I did it. I'm glad I did it because it
contributed to the collapse of the Soviet Union. My only regret is
that so many of my former friends who disagreed became bitter. I
stood up to an unreasonable majority which
wanted to stop the hydrogen bomb."
Dr. Edward Teller on his role in the development of
the hydrogen bomb, Seattle Times interview, 1995.
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"A bright light filled the plane. The first shock wave hit us. We
were eleven and a half slant miles from the atomic explosion, but
the whole airplane cracked and crinkled from the blast. I yelled
`flak!' thinking a heavy gun battery had found us."
Col. Paul Tibbets, pilot of the Enola Gay,
recounting the explosion at Hiroshima.
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I do not know with what weapons World War 3 will be fought,
but World War 4 will be fought with sticks and stones.
A. Einstein
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"It is a profound and necessary truth that the deep things in
science are not found because they are useful, they are found
because it was possible to find them."
J. Robert Oppenheimer.
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"You who are scientists may have been told that you are in part
responsible for the debacle (war) of today....but I assure you
that it is not the scientists of the world who are
responsible....What has come about has been caused solely by
those who would use, and are using, the progress that you have
made along lines of peace in an entirely different cause."
President Franklin D. Roosevelt, 1940.
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"To avert a vast, indefinite butchery, to bring the war to an end,
to give peace to the world, to lay healing hands upon its
tortured peoples by a manifestation of overwhelming power at
the cost of a few explosions seemed, after all our toils and
perils, a miracle of deliverance."
Winston Churchill in his history of World War II.
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"We can sum it up in one sentence: Our technical civilization has
just reached its greatest level of savagery. We will have to choose,
in the more or less near future, between collective suicide and the
intelligent use of our scientific conquests.......Before the terrifying
prospects now available to humanity, we see even more clearly
that peace is the only goal worth struggling for. This is no longer a
prayer but a demand to be made by all peoples to their
governments -- a demand to choose definitively between hell and
reason.”
Albert Camus, Combat, 8 August 1945
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Niels Bohr
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"Knowledge itself is the basis of civilization."
Niels Bohr.
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Nuclear Weapons Facts
• Total US nuclear weapons built, 1951-present: 67,500
• Peak number of weapons in US stockpile: 32,500 in 1967
• US nuclear bombs lost and never recovered: 11
• Number of US nuclear tests in the Pacific: 106
• Number of US nuclear tests in Nevada: 935
• States with most deployed nuclear weapons: Washington
and Georgia (1,450 each)
• Amount of plutonium still in weapons: 47 tons.
Source: Brookings Institution, Washington
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References
R. Rhodes, The Making of the Atomic Bomb
http://www.nuclearfiles.org/docs/bombing-hiroshima.html
http://www.dannen.com/szilard.html
http://seattletimes.nwsource.com/trinity/articles/part1.html
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