366 lines
20 KiB
Plaintext
366 lines
20 KiB
Plaintext
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"Within about 1ms after the explosion, some 70-80% of the explosion energy...
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is emitted as primary thermal radiation, most of which consists of soft
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X-rays."
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Glasstone, The Effects of Nuclear Weaponns
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FISSION PRINCIPLES
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The binding energy per nucleon versus atomic mass has a turning point around
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Fe-56. Iron is the most stable element. Elements with atomic masses less
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than iron tend to combine, and those with masses greater than iron tend to
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split. Radioactivity is an indication of this instability. The problem is that
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protons in the nucleus tend to repel each other. There comes a stage where
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the nuclear binding energy cannot compete with this repelling force, even if
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you add more and more neutrons to the nucleus. Take as an example, the highest
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Z naturally occuring element - uranium.
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U has many radioactive isotopes. These include U-234, U-235 and U-238. They are
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among the longest-living elements in a table of radioactive isotopes.
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The U-235 isotope is used in weapons since it has the highest fission cross
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section of all the U isotopes, for thermal neutrons.
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If you bombard U-238 with thermal neutrons, you might just cause
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a transuranic beta decay to Pu-239. Pu does not occur naturally, and is of
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use in weapons. If you bombard the radioactive isotopes with slow neutrons
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there is a chance that you will split the nuclei in half. In the process, you
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release some binding energy, and some more neutrons. For an explosion, you
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need a self-sustaining chain reaction which keeps on generating more and more
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neutrons. In effect, you need a critical mass of fissionable material to
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offset any loss of neutrons. (Instead of hitting other isotopic nuclei, the
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neutrons might just wander off.) A sphere of material is used to provide the
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least surface area for neutron loss. If the sphere is large enough, neutron
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loss will be balanced by neutron generation, resulting in a self-sustaining
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reaction. You have an energy release in fission since the mass of the original
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atom doesn't equal the mass of the two reaction atoms. The lost energy is
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converted to radiation and kinetic energy of the atoms via mass-energy
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equivalence. The fission products are around equal size, and are highly
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radioactive. Products include Sr, which is absorbed into human bones and
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stays there, since it is chemically similar to calcium. Other harmful
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products include cesium, similar to potassium. Cesium is distributed
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uniformly throughout the body.
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The number of fissioning nuclei increases as a geometric progression, with
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each generation. Most of the energy in a bomb is released during around the
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80th generation.
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It is estimated in 10^-6 secs, about 2x10-24 U-235 nuclei split, releasing
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HUGE amounts of energy. A single split gives you about 170MeV on average,
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whereas a chemical reaction only gives you a few eV.
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An example of a fission reaction is:
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U-235 + n -> Kr-92 + Xe-142 + 2n + 207 MeV.
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The released energy is many orders of magnitude greater than that released
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by a chemical reaction using the same amount of matter.
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A solid Pu sphere of 6.2kg mass is about 3.3" in diameter. It would be as
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big as a tennis ball, but as massive as a bowling ball. The sphere would be
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bigger if there was a Po-Be core inside.
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Uranium & Plutonium
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-------------------
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Uranium-235 is very difficult to extract. In fact, for every 25,000 tons
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of Uranium ore that is mined from the earth, only 50 tons of Uranium metal can
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be refined from that, and 99.3% of that metal is U-238 which is too stable to
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be used as an active agent in an atomic detonation. To make matters even more
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complicated, no ordinary chemical extraction can separate the two isotopes
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since both U-235 and U-238 possess precisely identical chemical
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characteristics. The only methods that can effectively separate U-235 from
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U-238 are mechanical methods.
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U-235 is slightly, but only slightly, lighter than its counterpart,
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U-238. A system of gaseous diffusion is used to begin the separating process
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between the two isotopes. In this system, Uranium is combined with fluorine
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to form Uranium Hexafluoride gas. This mixture is then propelled by low-
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pressure pumps through a series of extremely fine porous barriers. Because
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the U-235 atoms are lighter and thus propelled faster than the U-238 atoms,
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they could penetrate the barriers more rapidly. As a result, the
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U-235's concentration became successively greater as it passed through each
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barrier. After passing through several thousand barriers, the Uranium
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Hexafluoride contains a relatively high concentration of U-235 -- 2% pure
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Uranium in the case of reactor fuel, and if pushed further could
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(theoretically) yield up to 95% pure Uranium for use in an atomic bomb.
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Once the process of gaseous diffusion is finished, the Uranium must be
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refined once again. Magnetic separation of the extract from the previous
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enriching process is then implemented to further refine the Uranium. This
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involves electrically charging Uranium Tetrachloride gas and directing it past
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a weak electromagnet. Since the lighter U-235 particles in the gas stream are
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less affected by the magnetic pull, they can be gradually separated from the
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flow.
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Following the first two procedures, a third enrichment process is then
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applied to the extract from the second process. In this procedure, a gas
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centrifuge is brought into action to further separate the lighter U-235 from
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its heavier counter-isotope. Centrifugal force separates the two isotopes of
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Uranium by their mass. Once all of these procedures have been completed, all
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that need be done is to place the properly molded components of Uranium-235
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inside a warhead that will facilitate an atomic detonation.
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Supercritical mass for Uranium-235 is defined as 110 lbs (50 kgs) of
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pure Uranium.
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Depending on the refining process(es) used when purifying the U-235 for
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use, along with the design of the warhead mechanism and the altitude at which
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it detonates, the explosive force of the A-bomb can range anywhere from 1
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kiloton (which equals 1,000 tons of TNT) to 20 megatons (which equals 20
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million tons of TNT -- which, by the way, is the smallest strategic nuclear
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warhead we possess today. {Point in fact -- One Trident Nuclear Submarine
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carries as much destructive power as 25 World War II's}).
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While Uranium is an ideally fissionable material, it is not the only one.
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Plutonium can be used in an atomic bomb as well. By leaving U-238 inside an
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atomic reactor for an extended period of time, the U-238 picks up extra
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particles (neutrons especially) and gradually is transformed into the element
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Plutonium.
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Plutonium is fissionable, but not as easily fissionable as Uranium.
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While Uranium can be detonated by a simple 2-part gun-type device, Plutonium
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must be detonated by a more complex 32-part implosion chamber along with a
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stronger conventional explosive, a greater striking velocity and a
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simultaneous triggering mechanism for the conventional explosive packs. Along
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with all of these requirements comes the additional task of introducing a fine
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mixture of Beryllium and Polonium to this metal while all of these actions are
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occurring.
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Supercritical mass for Plutonium is defined as 35.2 lbs (16 kgs). This
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amount needed for a supercritical mass can be reduced to a smaller quantity of
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22 lbs (10 kgs) by surrounding the Plutonium with a U-238 casing.
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============================================================================
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- Diagram of a Chain Reaction -
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-------------------------------
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[1]------------------------------> o
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. o o .
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. o_0_o . <-----------------------[2]
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. o 0 o .
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. o o .
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\|/
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~
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. o o. .o o .
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[3]-----------------------> . o_0_o"o_0_o .
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. o 0 o~o 0 o .
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. o o.".o o .
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/ | \
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|/_ | _\|
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~~ | ~~
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o o | o o
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[4]-----------------> o_0_o | o_0_o <---------------[5]
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o~0~o | o~0~o
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o o ) | ( o o
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/ o \
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/ [1] \
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/ \
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/ \
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/ \
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o [1] [1] o
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. o o . . o o . . o o .
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. o_0_o . . o_0_o . . o_0_o .
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. o 0 o . <-[2]-> . o 0 o . <-[2]-> . o 0 o .
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. o o . . o o . . o o .
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/ | \
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|/_ \|/ _\|
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~~ ~ ~~
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. o o. .o o . . o o. .o o . . o o. .o o .
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. o_0_o"o_0_o . . o_0_o"o_0_o . . o_0_o"o_0_o .
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. o 0 o~o 0 o . <--[3]--> . o 0 o~o 0 o . <--[3]--> . o 0 o~o 0 o .
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. o o.".o o . . o o.".o o . . o o.".o o .
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. | . . | . . | .
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/ | \ / | \ / | \
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: | : : | : : | :
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: | : : | : : | :
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\:/ | \:/ \:/ | \:/ \:/ | \:/
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~ | ~ ~ | ~ ~ | ~
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[4] o o | o o [5] [4] o o | o o [5] [4] o o | o o [5]
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o_0_o | o_0_o o_0_o | o_0_o o_0_o | o_0_o
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o~0~o | o~0~o o~0~o | o~0~o o~0~o | o~0~o
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o o ) | ( o o o o ) | ( o o o o ) | ( o o
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/ | \ / | \ / | \
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/ | \ / | \ / | \
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/ | \ / | \ / | \
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/ | \ / | \ / | \
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/ o \ / o \ / o \
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/ [1] \ / [1] \ / [1] \
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o o o o o o
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[1] [1] [1] [1] [1] [1]
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============================================================================
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- Diagram Outline -
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---------------------
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[1] - Incoming Neutron
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[2] - Uranium-235
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[3] - Uranium-236
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[4] - Barium Atom
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[5] - Krypton Atom
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===========================================================================
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I. The History of the Atomic Bomb
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------------------------------
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On August 2nd 1939, just before the beginning of World War II, Albert
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Einstein wrote to then President Franklin D. Roosevelt. Einstein and several
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other scientists told Roosevelt of efforts in Nazi Germany to purify U-235
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with which might in turn be used to build an atomic bomb. It was shortly
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thereafter that the United States Government began the serious undertaking
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known only then as the Manhattan Project. Simply put, the Manhattan Project
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was committed to expedient research and production that would produce a viable
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atomic bomb.
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The most complicated issue to be addressed was the production of ample
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amounts of `enriched' uranium to sustain a chain reaction. At the time,
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Uranium-235 was very hard to extract. In fact, the ratio of conversion from
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Uranium ore to Uranium metal is 500:1. An additional drawback is that the 1
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part of Uranium that is finally refined from the ore consists of over 99%
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Uranium-238, which is practically useless for an atomic bomb. To make it even
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more difficult, U-235 and U-238 are precisely similar in their chemical
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makeup. This proved to be as much of a challenge as separating a solution of
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sucrose from a solution of glucose. No ordinary chemical extraction could
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separate the two isotopes. Only mechanical methods could effectively separate
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U-235 from U-238. Several scientists at Columbia University managed to solve
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this dilemma.
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A massive enrichment laboratory/plant was constructed at Oak Ridge,
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Tennessee. H.C. Urey, along with his associates and colleagues at Columbia
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University, devised a system that worked on the principle of gaseous
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diffusion. Following this process, Ernest O. Lawrence (inventor of the
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Cyclotron) at the University of California in Berkeley implemented a process
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involving magnetic separation of the two isotopes.
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Following the first two processes, a gas centrifuge was used to further
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separate the lighter U-235 from the heavier non-fissionable U-238 by their
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mass. Once all of these procedures had been completed, all that needed to be
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done was to put to the test the entire concept behind atomic fission.
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Over the course of six years, ranging from 1939 to 1945, more than 2
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billion dollars were spent on the Manhattan Project. The formulas for
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refining Uranium and putting together a working bomb were created and seen to
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their logical ends by some of the greatest minds of our time. Among these
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people who unleashed the power of the atomic bomb was J. Robert Oppenheimer.
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Oppenheimer was the major force behind the Manhattan Project. He
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literally ran the show and saw to it that all of the great minds working on
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this project made their brainstorms work. He oversaw the entire project from
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its conception to its completion.
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Finally the day came when all at Los Alamos would find out whether or not
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The Gadget (code-named as such during its development) was either going to be
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the colossal dud of the century or perhaps end the war. It all came down to
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a fateful morning of midsummer, 1945.
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At 5:29:45 (Mountain War Time) on July 16th, 1945, in a white blaze that
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stretched from the basin of the Jemez Mountains in northern New Mexico to the
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still-dark skies, The Gadget ushered in the Atomic Age. The light of the
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explosion then turned orange as the atomic fireball began shooting upwards at
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360 feet per second, reddening and pulsing as it cooled. The characteristic
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mushroom cloud of radioactive vapor materialized at 30,000 feet. Beneath the
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cloud, all that remained of the soil at the blast site were fragments of jade
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green radioactive glass. ...All of this caused by the heat of the reaction.
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The brilliant light from the detonation pierced the early morning skies
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with such intensity that residents from a faraway neighboring community would
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swear that the sun came up twice that day. Even more astonishing is that a
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blind girl saw the flash 120 miles away.
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Upon witnessing the explosion, reactions among the people who created
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it were mixed. Isidor Rabi felt that the equilibrium in nature had been
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upset -- as if humankind had become a threat to the world it inhabited.
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J. Robert Oppenheimer, though ecstatic about the success of the project,
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quoted a remembered fragment from Bhagavad Gita. "I am become Death," he
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said, "the destroyer of worlds." Ken Bainbridge, the test director, told
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Oppenheimer, "Now we're all sons of bitches."
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Several participants, shortly after viewing the results, signed petitions
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against loosing the monster they had created, but their protests fell on deaf
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ears. As it later turned out, the Jornada del Muerto of New Mexico was not
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the last site on planet Earth to experience an atomic explosion.
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As many know, atomic bombs have been used only twice in warfare. The
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first and foremost blast site of the atomic bomb is Hiroshima. A Uranium
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bomb (which weighed in at over 4 & 1/2 tons) nicknamed "Little Boy" was
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dropped on Hiroshima August 6th, 1945. The Aioi Bridge, one of 81 bridges
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connecting the seven-branched delta of the Ota River, was the aiming point of
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the bomb. Ground Zero was set at 1,980 feet. At 0815 hours, the bomb was
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dropped from the Enola Gay. It missed by only 800 feet. At 0816 hours, in
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the flash of an instant, 66,000 people were killed and 69,000 people were
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injured by a 10 kiloton atomic explosion.
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The point of total vaporization from the blast measured one half of a
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mile in diameter. Total destruction ranged at one mile in diameter. Severe
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blast damage carried as far as two miles in diameter. At two and a half
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miles, everything flammable in the area burned. The remaining area of the
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blast zone was riddled with serious blazes that stretched out to the final
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edge at a little over three miles in diameter.
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On August 9th 1945, Nagasaki fell to the same treatment as Hiroshima.
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Only this time, a Plutonium bomb nicknamed "Fat Man" was dropped on the city.
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Even though the "Fat Man" missed by over a mile and a half, it still leveled
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nearly half the city. Nagasaki's population dropped in one split-second from
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422,000 to 383,000. 39,000 were killed, over 25,000 were injured. That
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blast was less than 10 kilotons as well. Estimates from physicists who have
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studied each atomic explosion state that the bombs that were used had utilized
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only 1/10th of 1 percent of their respective explosive capabilities.
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While the mere explosion from an atomic bomb is deadly enough, its
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destructive ability doesn't stop there. Atomic fallout creates another hazard
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as well. The rain that follows any atomic detonation is laden with
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radioactive particles. Many survivors of the Hiroshima and Nagasaki blasts
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succumbed to radiation poisoning due to this occurance.
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The atomic detonation also has the hidden lethal surprise of affecting
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the future generations of those who live through it. Leukemia is among the
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|
|
greatest of afflictions that are passed on to the offspring of survivors.
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While the main purpose behind the atomic bomb is obvious, there are many
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|
by-products that have been brought into consideration in the use of all
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|
|
weapons atomic. With one small atomic bomb, a massive area's communications,
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|
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travel and machinery will grind to a dead halt due to the EMP (Electro-
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|
|
Magnetic Pulse) that is radiated from a high-altitude atomic detonation.
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|
These high-level detonations are hardly lethal, yet they deliver a serious
|
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|
|
enough EMP to scramble any and all things electronic ranging from copper wires
|
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|
all the way up to a computer's CPU within a 50 mile radius.
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At one time, during the early days of The Atomic Age, it was a popular
|
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|
|
notion that one day atomic bombs would one day be used in mining operations
|
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|
|
and perhaps aid in the construction of another Panama Canal. Needless to say,
|
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|
|
it never came about. Instead, the military applications of atomic destruction
|
||
|
|
increased. Atomic tests off of the Bikini Atoll and several other sites were
|
||
|
|
common up until the Nuclear Test Ban Treaty was introduced. Photos of nuclear
|
||
|
|
test sites here in the United States can be obtained through the Freedom of
|
||
|
|
Information Act.
|
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|
|
||
|
|
[See Smyth Report for fuller details. Goin's book in References has photos
|
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|
|
of nuke sites.]
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============================================================================
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|
1994
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