Once the air pressure has achieved the desired level, the magnetic bubble will snap back into its original position and strike the contact, thus completing the circuit and setting off the explosive(s).
Detonating Head
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The detonating head (or heads, depending on whether a Uranium or Plutonium bomb is being used as a model) that is seated in the conventional explosive charge(s) is similar to the standard-issue blasting cap. It merely serves as a catalyst to bring about a greater explosion. Calibration of this device is essential. Too small of a detonating head will only cause a colossal dud that will be doubly dangerous since someone's got to disarm and re-fit the bomb with another detonating head. (an added measure of discomfort comes from the knowledge that the conventional explosive may have detonated with insufficient force to weld the radioactive metals. This will cause a supercritical mass that could go off at any time.) The detonating head will receive an electric charge from the either the air pressure detonator or the radar altimeter's coordinating detonator, depending on what type of system is used. The Du Pont company makes rather excellent blasting caps that can be easily modified to suit the required specifications.
Conventional Explosive Charge(s)
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This explosive is used to introduce (and weld) the lesser amount of Uranium to the greater amount within the bomb's housing. [The amount of pressure needed to bring this about is unknown and possibly classified by the United States Government for reasons of National Security]
Plastic explosives work best in this situation since they can be manipulated to enable both a Uranium bomb and a Plutonium bomb to detonate. One very good explosive is Urea Nitrate. The directions on how to make Urea Nitrate are as follows:
- Ingredients
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[1] 1 cup concentrated solution of uric acid (C5 H4 N4 O3)
[2] 1/3 cup of nitric acid
[3] 4 heat-resistant glass containers
[4] 4 filters (coffee filters will do)
Filter the concentrated solution of uric acid through a filter to remove impurities. Slowly add 1/3 cup of nitric acid to the solution and let the mixture stand for 1 hour. Filter again as before. This time the Urea Nitrate crystals will collect on the filter. Wash the crystals by pouring water over them while they are in the filter. Remove the crystals from the filter and allow 16 hours for them to dry. This explosive will need a blasting cap to detonate.
It may be necessary to make a quantity larger than the aforementioned list calls for to bring about an explosion great enough to cause the Uranium (or Plutonium) sections to weld together on impact.
Neutron Deflector
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The neutron deflector is comprised solely of Uranium-238. Not only is U-238 non-fissionable, it also has the unique ability to reflect neutrons back to their source.
The U-238 neutron deflector can serve 2 purposes. In a Uranium bomb, the neutron deflector serves as a safeguard to keep an accidental supercritical mass from occurring by bouncing the stray neutrons from the `bullet' counterpart of the Uranium mass away from the greater mass below it (and viceversa). The neutron deflector in a Plutonium bomb actually helps the wedges of Plutonium retain their neutrons by `reflecting' the stray particles back into the center of the assembly. [See diagram in Section 4 of this file.]
Uranium Plutonium
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Uranium-235 is very difficult to extract. In fact, for every 25,000 tons of Uranium ore that is mined from the earth, only 50 tons of Uranium metal can be refined from that, and 99.3% of that metal is U-238 which is too stable to be used as an active agent in an atomic detonation. To make matters even more complicated, no ordinary chemical extraction can separate the two isotopes since both U-235 and U-238 possess precisely identical chemical characteristics. The only methods that can effectively separate U-235 from U-238 are mechanical methods.
U-235 is slightly, but only slightly, lighter than its counterpart, U-238. A system of gaseous diffusion is used to begin the separating process between the two isotopes. In this system, Uranium is combined with fluorine to form Uranium Hexafluoride gas. This mixture is then propelled by lowpressure pumps through a series of extremely fine porous barriers. Because the U-235 atoms are lighter and thus propelled faster than the U-238 atoms, they could penetrate the barriers more rapidly. As a result, the U-235's concentration became successively greater as it passed through each barrier. After passing through several thousand barriers, the Uranium Hexafluoride contains a relatively high concentration of U-235 -- 2% pure Uranium in the case of reactor fuel, and if pushed further could (theoretically) yield up to 95% pure Uranium for use in an atomic bomb.
Once the process of gaseous diffusion is finished, the Uranium must be refined once again. Magnetic separation of the extract from the previous enriching process is then implemented to further refine the Uranium. This involves electrically charging Uranium Tetrachloride gas and directing it past a weak electromagnet. Since the lighter U-235 particles in the gas stream are less affected by the magnetic pull, they can be gradually separated from the flow.
Following the first two procedures, a third enrichment process is then applied to the extract from the second process. In this procedure, a gas centrifuge is brought into action to further separate the lighter U-235 from its heavier counter-isotope. Centrifugal force separates the two isotopes of Uranium by their mass. Once all of these procedures have been completed, all that need be done is to place the properly molded components of Uranium-235 inside a warhead that will facilitate an atomic detonation.
Supercritical mass for Uranium-235 is defined as 110 lbs (50 kgs) of pure Uranium.
Depending on the refining process(es) used when purifying the U-235 for use, along with the design of the warhead mechanism and the altitude at which it detonates, the explosive force of the A-bomb can range anywhere from 1 kiloton (which equals 1,000 tons of TNT) to 20 megatons (which equals 20 million tons of TNT -- which, by the way, is the smallest strategic nuclear warhead we possess today. {Point in fact -- One Trident Nuclear Submarine carries as much destructive power as 25 World War II's}).
While Uranium is an ideally fissionable material, it is not the only one. Plutonium can be used in an atomic bomb as well. By leaving U-238 inside an atomic reactor for an extended period of time, the U-238 picks up extra particles (neutrons especially) and gradually is transformed into the element Plutonium.
Plutonium is fissionable, but not as easily fissionable as Uranium. While Uranium can be detonated by a simple 2-part gun-type device, Plutonium must be detonated by a more complex 32-part implosion chamber along with a stronger conventional explosive, a greater striking velocity and a simultaneous triggering mechanism for the conventional explosive packs. Along with all of these requirements comes the additional task of introducing a fine mixture of Beryllium and Polonium to this metal while all of these actions are occurring.
Supercritical mass for Plutonium is defined as 35.2 lbs (16 kgs). This amount needed for a supercritical mass can be reduced to a smaller quantity of 22 lbs (10 kgs) by surrounding the Plutonium with a U-238 casing.
To illustrate the vast difference between a Uranium gun-type detonator and a Plutonium implosion detonator, here is a quick rundown.
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[1] Uranium Detonator
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Comprised of 2 parts. Larger mass is spherical and concave.