Enter the time warp
To understand the difficulty of
inventing the
H-bomb, take a mental journey to 1945. Atomic ("fission")
bombs have
just closed World War II with a double-bang. For more than
two years,
Los Alamos, New Mexico has been world headquarters for
physicists,
home to the intense intellectual debates and frantic
engineering needed
to build the atomic bomb. But
the exhilaration at Los Alamos is soured by the
realization that
the "project" has killed more than 100,000 people and
forever tipped
the military balance toward offense. A week after
Nagasaki, Manhattan
Project leader J. Robert Oppenheimer is "guilty, weary and
depressed,
wondering if the dead at Hiroshima and Nagasaki were not
luckier
than the survivors, whose exposure to the bombs would have
lifetime
effects," wrote Richard Rhodes in his history of the
hydrogen bomb.
The leaders of the bomb project write that "the safety of
this nation...
cannot lie wholly or even primarily in its scientific or
technical
prowess. It can only be based on making future wars
impossible"
(see p. 203, "Dark Sun... " in the bibliography.
While Los Alamos continues
working on the
atomic bomb, and takes faltering steps toward a hydrogen
bomb, many
physicists, satisfied that their goal is met and uncertain
about
building a hydrogen bomb based on the vastly greater
energy of fusion,
return to their universities.
Fusion
confusion: the
terrible terminology of fission and fusion
Nuclear energy comes
from two
distinct sources—fission
and fusion:
Fission
("splitting") occurs
when the nucleus of large, unstable atoms, like uranium
and plutonium,
break into smaller atoms, releasing energetic radiation
and neutrons.
Fission powers the "atomic" bomb that destroyed Hiroshima, and all nuclear power reactors.
Fusion
("joining") occurs when
light atoms, primarily isotopes of hydrogen, fuse into
larger atoms,
releasing fantastic quantities of energy. Fusion powers
the sun
and "hydrogen" bombs, which are called "thermonuclear" for
the intense
heat needed to overcome electrical repulsion between
positively-charged
hydrogen nuclei. Fusion, however, is extremely difficult
to control;
although billions have been spent to tame fusion for
electricity,
practical reactors are decades away.
In bombs, the two forms of nuclear
energy are
often blended. Most fission bombs are "boosted" with
fusion fuel.
All fusion bombs are triggered by fission bombs, and most
contain
a second fission bomb, called a "spark plug."
In 1946, Edward Teller departs for the
University
of Chicago. One of several brilliant Hungarian refugees who
contributed
mightily to the atomic bomb, Teller had earned his Ph.D.
under the
eminent German physicist Werner Heisenberg and moved to the
United
States in 1933, after the Nazis took power in Germany.
A 'super' bomb?
Teller's interest in the hydrogen bomb dated to 1941, when Italian
physicist Enrico Fermi floated the idea. Although the fusion bomb
(called the 'super') got some attention, leaders of the Manhattan
Project decided to defer the difficult challenge of fusion until they
had learned to make a fission weapon from uranium and plutonium. (For
one thing, fission could be tested in the laboratory, while fusion
requires conditions more like the center of the sun than the top of a
New Mexican mesa. And the physicists understood that a fusion bomb would
need a fission trigger.)
While the Manhattan Project tried to tackle first things first, Teller
dwelled on fusing two isotopes of hydrogen --deuterium and tritium.
(Isotopes are atoms that are chemically identical but have a different
neutron count and different masses.) "Even during the war he was
troublesome," says physicist Herbert York. "He wanted to work on fusion,
but the job was fission, and he quit in a huff several times."
Under earthly conditions,
electrical repulsion
prevents hydrogen nuclei from fusing. In the sun, however,
enormous
gravitation squeezes hydrogen nuclei until they fuse into
helium.
Gobs of energy are released when a bit of their mass is
converted
to energy according to Einstein's famous equation, E=MC2
(Energy equals mass times the speed of light, squared).
The Apache H-bomb test, July, 8,
1956 on Eniwetok
atoll. In 1963, health concerns about radioactive fallout
led to
a ban on atmospheric testing. Photo:
Department
of Energy
Shocking truth
Scientists had known since the 1930s about fusion in the sun, but fusion
refused to be "tamed" into a bomb on Earth, and even after the war,
fusion was not the focus at Los Alamos. Then the Cold War intensified:
The 1948 Berlin blockade, the 1949 Soviet atomic bomb test, and the
start of the Korean war in 1950 created new political realities. In
1950, President Harry Truman made the H-bomb a national priority.
In June, 1950, however a long series of calculations proved that
Teller's super design would fail. The calculations, made in those
pre-computer days with slide rules and mechanical calculators, were
incredibly complex, says Carey Sublette, author of Nuclear Weapons
Frequently Asked Questions and operator of the Nuclear Weapon Archive
website. "There are a lot of processes involved that could pull the
outcome in different directions, and all are significant, so you can't
simplify the problem by assuming things away, as you frequently can do
in science .... Very complicated computations were needed to chart what
was going to happen."
The answer, delivered by mathematician Stanislaw Ulam, was that the
fusion fuel would either not start fusing, or the fission trigger would
blow the fuel apart too soon. Then, in January, 1951, Ulam, who had
immersed himself in matters thermonuclear, suggested using energy from
the fission bomb to compress, not heat, the fusion fuel.
Although Teller had long argued "compression does not matter," Ulam
realized, according to Rhodes, that "Compression works in thermonuclear
fuels in much the same way it works in fission fuels, squeezing nuclei
closer together and therefore improving their chances of interacting"
(Dark Sun, p. 464). Compression also makes the fuel easier to heat with
thermal radiation and slower to cool, Sublette adds.
Although Teller soon scented success, shock from the atomic bomb might
not compress the fuel evenly, and the secondary might still be destroyed
too soon. So Teller built on Ulam's idea by suggesting that the
compression could come from thermal X-rays from the primary bomb, not
the shock wave.
In the Teller-Ulam hydrogen
bomb design,
high explosive compresses fission fuel in the "primary"
stage. Intense
X-rays from the atomic explosion move through the
radiation channel,
vaporizing the uranium pusher-tamper, which acts like an
inside-out
rocket, compressing the fusion fuel and spark plug to
extreme density.
The spark plug becomes a second fission bomb, heating the
fusion
fuel and igniting the fusion reaction. The uranium shield
protects
the secondary from destruction while fusion occurs; the
explosion
is over in microseconds. Diagram:
Adapted from Carey Sublette, Nuclear Weapon Archive
The different was subtle, but critical. Radiation moves at the speed of
light, much faster than a shock wave, and radiation can be directed to
compress the fuel evenly from all directions so quickly that fusion can
occur before the shock wave destroys the secondary.
Teller then contributed another idea: placing a "spark plug" of uranium
or plutonium in the center of the fusion stage. The spark plug,
compressed by the radiation implosion, would fission, heating and
igniting fusion in the already compressed fusion fuel. The result, the
"Teller-Ulam" design for a thermonuclear weapon, remains the standard
design 50 years after it was invented.
The stage was set for the monster, Mike. On Nov. 1, 1952, the world's
first hydrogen bomb created a mushroom cloud 100 miles across and proved
what physicists suspected - that while there was an upper limit to the
size of fission bombs, hydrogen bombs could be made as big as you
wished.
To understand the difficulty of
inventing the
H-bomb, take a mental journey to 1945. Atomic ("fission")
bombs have
just closed World War II with a double-bang. For more than
two years,
Los Alamos, New Mexico has been world headquarters for
physicists,
home to the intense intellectual debates and frantic
engineering needed
to build the atomic bomb. But
the exhilaration at Los Alamos is soured by the
realization that
the "project" has killed more than 100,000 people and
forever tipped
the military balance toward offense. A week after
Nagasaki, Manhattan
Project leader J. Robert Oppenheimer is "guilty, weary and
depressed,
wondering if the dead at Hiroshima and Nagasaki were not
luckier
than the survivors, whose exposure to the bombs would have
lifetime
effects," wrote Richard Rhodes in his history of the
hydrogen bomb.
The leaders of the bomb project write that "the safety of
this nation...
cannot lie wholly or even primarily in its scientific or
technical
prowess. It can only be based on making future wars
impossible"
(see p. 203, "Dark Sun... " in the bibliography.
While Los Alamos continues
working on the
atomic bomb, and takes faltering steps toward a hydrogen
bomb, many
physicists, satisfied that their goal is met and uncertain
about
building a hydrogen bomb based on the vastly greater
energy of fusion,
return to their universities.
Fusion
confusion: the
terrible terminology of fission and fusion
Nuclear energy comes
from two
distinct sources—fission
and fusion:
Fission
("splitting") occurs
when the nucleus of large, unstable atoms, like uranium
and plutonium,
break into smaller atoms, releasing energetic radiation
and neutrons.
Fission powers the "atomic" bomb that destroyed Hiroshima, and all nuclear power reactors.
Fusion
("joining") occurs when
light atoms, primarily isotopes of hydrogen, fuse into
larger atoms,
releasing fantastic quantities of energy. Fusion powers
the sun
and "hydrogen" bombs, which are called "thermonuclear" for
the intense
heat needed to overcome electrical repulsion between
positively-charged
hydrogen nuclei. Fusion, however, is extremely difficult
to control;
although billions have been spent to tame fusion for
electricity,
practical reactors are decades away.
In bombs, the two forms of nuclear
energy are
often blended. Most fission bombs are "boosted" with
fusion fuel.
All fusion bombs are triggered by fission bombs, and most
contain
a second fission bomb, called a "spark plug."
In 1946, Edward Teller departs for the
University
of Chicago. One of several brilliant Hungarian refugees who
contributed
mightily to the atomic bomb, Teller had earned his Ph.D.
under the
eminent German physicist Werner Heisenberg and moved to the
United
States in 1933, after the Nazis took power in Germany.
A 'super' bomb?
Teller's interest in the hydrogen bomb dated to 1941, when Italian
physicist Enrico Fermi floated the idea. Although the fusion bomb
(called the 'super') got some attention, leaders of the Manhattan
Project decided to defer the difficult challenge of fusion until they
had learned to make a fission weapon from uranium and plutonium. (For
one thing, fission could be tested in the laboratory, while fusion
requires conditions more like the center of the sun than the top of a
New Mexican mesa. And the physicists understood that a fusion bomb would
need a fission trigger.)
While the Manhattan Project tried to tackle first things first, Teller
dwelled on fusing two isotopes of hydrogen --deuterium and tritium.
(Isotopes are atoms that are chemically identical but have a different
neutron count and different masses.) "Even during the war he was
troublesome," says physicist Herbert York. "He wanted to work on fusion,
but the job was fission, and he quit in a huff several times."
Under earthly conditions,
electrical repulsion
prevents hydrogen nuclei from fusing. In the sun, however,
enormous
gravitation squeezes hydrogen nuclei until they fuse into
helium.
Gobs of energy are released when a bit of their mass is
converted
to energy according to Einstein's famous equation, E=MC2
(Energy equals mass times the speed of light, squared).
The Apache H-bomb test, July, 8,
1956 on Eniwetok
atoll. In 1963, health concerns about radioactive fallout
led to
a ban on atmospheric testing. Photo:
Department
of Energy
Shocking truth
Scientists had known since the 1930s about fusion in the sun, but fusion
refused to be "tamed" into a bomb on Earth, and even after the war,
fusion was not the focus at Los Alamos. Then the Cold War intensified:
The 1948 Berlin blockade, the 1949 Soviet atomic bomb test, and the
start of the Korean war in 1950 created new political realities. In
1950, President Harry Truman made the H-bomb a national priority.
In June, 1950, however a long series of calculations proved that
Teller's super design would fail. The calculations, made in those
pre-computer days with slide rules and mechanical calculators, were
incredibly complex, says Carey Sublette, author of Nuclear Weapons
Frequently Asked Questions and operator of the Nuclear Weapon Archive
website. "There are a lot of processes involved that could pull the
outcome in different directions, and all are significant, so you can't
simplify the problem by assuming things away, as you frequently can do
in science .... Very complicated computations were needed to chart what
was going to happen."
The answer, delivered by mathematician Stanislaw Ulam, was that the
fusion fuel would either not start fusing, or the fission trigger would
blow the fuel apart too soon. Then, in January, 1951, Ulam, who had
immersed himself in matters thermonuclear, suggested using energy from
the fission bomb to compress, not heat, the fusion fuel.
Although Teller had long argued "compression does not matter," Ulam
realized, according to Rhodes, that "Compression works in thermonuclear
fuels in much the same way it works in fission fuels, squeezing nuclei
closer together and therefore improving their chances of interacting"
(Dark Sun, p. 464). Compression also makes the fuel easier to heat with
thermal radiation and slower to cool, Sublette adds.
Although Teller soon scented success, shock from the atomic bomb might
not compress the fuel evenly, and the secondary might still be destroyed
too soon. So Teller built on Ulam's idea by suggesting that the
compression could come from thermal X-rays from the primary bomb, not
the shock wave.
In the Teller-Ulam hydrogen
bomb design,
high explosive compresses fission fuel in the "primary"
stage. Intense
X-rays from the atomic explosion move through the
radiation channel,
vaporizing the uranium pusher-tamper, which acts like an
inside-out
rocket, compressing the fusion fuel and spark plug to
extreme density.
The spark plug becomes a second fission bomb, heating the
fusion
fuel and igniting the fusion reaction. The uranium shield
protects
the secondary from destruction while fusion occurs; the
explosion
is over in microseconds. Diagram:
Adapted from Carey Sublette, Nuclear Weapon Archive
The different was subtle, but critical. Radiation moves at the speed of
light, much faster than a shock wave, and radiation can be directed to
compress the fuel evenly from all directions so quickly that fusion can
occur before the shock wave destroys the secondary.
Teller then contributed another idea: placing a "spark plug" of uranium
or plutonium in the center of the fusion stage. The spark plug,
compressed by the radiation implosion, would fission, heating and
igniting fusion in the already compressed fusion fuel. The result, the
"Teller-Ulam" design for a thermonuclear weapon, remains the standard
design 50 years after it was invented.
The stage was set for the monster, Mike. On Nov. 1, 1952, the world's
first hydrogen bomb created a mushroom cloud 100 miles across and proved
what physicists suspected - that while there was an upper limit to the
size of fission bombs, hydrogen bombs could be made as big as you
wished.
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