Sam Wormley
2015-08-08 17:25:26 UTC
How Physics Drove the Design of the Atomic Bombs Dropped on Japan
http://www.smithsonianmag.com/science-nature/how-physics-drove-design-atomic-bombs-dropped-japan-180956172/
For many scientists involved in the Manhattan Project, the race to
build an atomic bomb was a grim battle between life and death. There
was no denying the technology's destructive force or its inevitable
civilian toll. After the bombings of Hiroshima and Nagasaki, which
took place 70 years ago this week, scientific director J. Robert
Oppenheimer famously recalled his feelings upon hearing the news,
quoting from a Hindu text: "Now I am become Death, the destroyer of
worlds."
But in the grip of World War II, with German scientists furtively
working on the same technology, Oppenheimer and other physicists in
the U.S. were keenly focused on the task of creating the world's
first nuclear weapon. And within the secret confines of Los Alamos
National Laboratory, an internal battle was raging between two groups
with opposing ideas for how to deliver the deadly payload.
Ultimately, two types of bomb using different radioactive materials
fell on Japan just days apart, codenamed Little Boy and Fat Man. But
if scientists had succeeded in their first attempts, both bombs could
have been named Thin Man.
The nucleus of an atom is a more variable place than you might
imagine. At its heart, an atom contains a mix of particles called
protons and neutrons, which combine to give the atom its mass and its
unique elemental personality. While all atoms of a given chemical
element have the same number of protons, the neutron count can vary,
yielding isotopes of different masses. But like an overcrowded raft,
some isotopes teeter on the edge of stability and are prone to
spontaneously tossing out excess energy and particles in the form of
radiation. Over time, radioactive isotopes naturally decay into more
stable configurations and even into new elements in a fairly
predictable chain of events.
Harnessing the atom to create an explosion didn't seem realistic
until 1939, when scientists in Berlin managed to deliberately split a
uranium atom into lighter elements. Induced in the right way, this
process of nuclear fission can release enormous amounts of
energy—according to initial reports by The New York Times, the bomb
dropped on Hiroshima exploded with the force of 20,000 tons of TNT,
although that estimate has since been downgraded to 15,000 tons.
In a 1939 letter to U.S. President Franklin Roosevelt, Albert
Einstein warned of the fission experiment and Nazi efforts to build a
weapon. Soon after, scientists showed just how much uranium would be
needed to achieve critical mass and detonate a fission bomb, and they
proved that they could also use plutonium for the task. By 1941, the
Manhattan Project had joined the race to develop a working atomic
bomb.
http://www.smithsonianmag.com/science-nature/how-physics-drove-design-atomic-bombs-dropped-japan-180956172/#tm0j61ku8EIhXlOK.99
For many scientists involved in the Manhattan Project, the race to
build an atomic bomb was a grim battle between life and death. There
was no denying the technology's destructive force or its inevitable
civilian toll. After the bombings of Hiroshima and Nagasaki, which
took place 70 years ago this week, scientific director J. Robert
Oppenheimer famously recalled his feelings upon hearing the news,
quoting from a Hindu text: "Now I am become Death, the destroyer of
worlds."
But in the grip of World War II, with German scientists furtively
working on the same technology, Oppenheimer and other physicists in
the U.S. were keenly focused on the task of creating the world's
first nuclear weapon. And within the secret confines of Los Alamos
National Laboratory, an internal battle was raging between two groups
with opposing ideas for how to deliver the deadly payload.
Ultimately, two types of bomb using different radioactive materials
fell on Japan just days apart, codenamed Little Boy and Fat Man. But
if scientists had succeeded in their first attempts, both bombs could
have been named Thin Man.
The nucleus of an atom is a more variable place than you might
imagine. At its heart, an atom contains a mix of particles called
protons and neutrons, which combine to give the atom its mass and its
unique elemental personality. While all atoms of a given chemical
element have the same number of protons, the neutron count can vary,
yielding isotopes of different masses. But like an overcrowded raft,
some isotopes teeter on the edge of stability and are prone to
spontaneously tossing out excess energy and particles in the form of
radiation. Over time, radioactive isotopes naturally decay into more
stable configurations and even into new elements in a fairly
predictable chain of events.
Harnessing the atom to create an explosion didn't seem realistic
until 1939, when scientists in Berlin managed to deliberately split a
uranium atom into lighter elements. Induced in the right way, this
process of nuclear fission can release enormous amounts of
energy—according to initial reports by The New York Times, the bomb
dropped on Hiroshima exploded with the force of 20,000 tons of TNT,
although that estimate has since been downgraded to 15,000 tons.
In a 1939 letter to U.S. President Franklin Roosevelt, Albert
Einstein warned of the fission experiment and Nazi efforts to build a
weapon. Soon after, scientists showed just how much uranium would be
needed to achieve critical mass and detonate a fission bomb, and they
proved that they could also use plutonium for the task. By 1941, the
Manhattan Project had joined the race to develop a working atomic
bomb.
http://www.smithsonianmag.com/science-nature/how-physics-drove-design-atomic-bombs-dropped-japan-180956172/#tm0j61ku8EIhXlOK.99
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sci.physics is an unmoderated newsgroup dedicated
to the discussion of physics, news from the physics
community, and physics-related social issues.