Bill,
     Here is some info I dredged up that is not classified. It
 covers the type of weapons that were used in the 1950's. The
 fissle materal was not inserted until a war situation existed.
     The bomber crew did this... Nothing but HE until it was
 even inserted, it could burn and not explode. read this little
 bit which has been released. Many encyclopedias have diagrams
 of both types... Fusion weapons are another thing.
 The following is extracted from InfoPedia 2.0 (c) Soft Key 1996
 NUCLEAR WEAPONS,
     explosive devices, designed to release nuclear energy on a large
 scale, used primarily in military applications.
     The first atomic bomb (or A-bomb), which was tested on July 16,
 1945, at Alamogordo, N. Mex., represented a completely new type of
 artificial explosive. All explosives prior to that time derived
 their power from the rapid burning or decomposition of some chemical
 compound. Such chemical processes release only the energy of the
 outermost electrons in the atom.
 Fission Weapons.
     The light isotope of uranium, uranium-235, is easily split by
 the fission neutrons and, upon fission, emits an average of about
 2.5 neutrons. One neutron per generation of nuclear fissions is
 necessary to sustain the chain reactions. Others may be lost by
 escape from the mass of chain-reacting material, or they may be
 absorbed in impurities or in the heavy uranium isotope, uranium-238,
 if it is present. Any substance capable of sustaining a fission
 chain reaction is known as a fissile material.
 Critical mass.
     A small sphere of pure fissile material, such as uranium-235,
 about the size of a golf ball, would not sustain a chain reaction.
 Too many neutrons escape through the surface area, which is rela-
 tively large compared with its volume, and thus are lost to the
 chain reaction. In a mass of uranium-235 about the size of a base-
 ball, however, the number of neutrons lost through the surface is
 compensated for by the neutrons generated in additional fissions
 taking place within the sphere. The minimum amount of fissile
 material (of a given shape) required to maintain the chain reaction
 is known as the critical mass. Increasing the size of the sphere
 produces a supercritical assembly, in which the successive gener-
 ations of fissions increase very rapidly, leading to a possible
 explosion as a result of the extremely rapid release of a large
 amount of energy. In an atomic bomb, therefore, a mass of fissile
 material greater than the critical size must be assembled instan-
 taneously and held together for about a millionth of a second to
 permit the chain reaction to propagate before the bomb explodes. A
 heavy material, called a tamper, surrounds the fissile mass and
 prevents its premature disruption. The tamper also reduces the
 number of neutrons that escape.
     If every atom in 0.5 kg (1.1 lb) of uranium were to split,
 the energy produced would equal the explosive power of 9.9 kilo-
 tons of TNT.  In this hypothetical case, the efficiency of the
 process would be 100 percent. In the first A-bomb tests, this kind
 of efficiency was not approached. Moreover, a 0.5-kg (1.1-lb) mass
 is too small for a critical assembly.
  Detonation of atomic bombs.
     Various systems have been devised to detonate the atomic bomb.
 The simplest system is the gun-type weapon, in which a projectile
 made of fissile material is fired at a target of the same material
 so that the two weld together into a supercritical assembly. The
 atomic bomb exploded by the U.S. over Hiroshima, Japan, on Aug. 6,
 1945, was a gun-type weapon. It had the energy equivalent of about
 20 kilotons of TNT. (To the best of knowledge, the only one of this
 type ever made. Jim)
     A more complex method, known as implosion, is utilized in a
 spherically shaped weapon. The outer part of the sphere consists
 of a layer of closely fitted and specially shaped devices, called
 lenses, consisting of high explosive and designed to concentrate
 the blast toward the center of the bomb. Each segment of the high
 explosive is equipped with a detonator, which in turn is wired to
 all other segments. An electrical impulse explodes all the chunks
 of high explosive simultaneously, resulting in a detonation wave
 that converges toward the core of the weapon.
     At the core is a sphere of fissile material, which is compressed
 by the powerful, inwardly directed pressure, or implosion. The den-
 sity of the metal is increased, and a supercritical assembly is
 produced.
    (Here is the part---If the core has not been inserted, there can
 be no detonation... or spread of material. Think about it. Jim)
     The Alamogordo test bomb, as well as the one dropped by the U.S.
 on Nagasaki, Japan, on Aug. 9, 1945, were of the implosion type.
 Each was equivalent to about 20 kilotons of TNT.
     Regardless of the method used to attain a supercritical assembly,
 the chain reaction proceeds for about a millionth of a second, lib-
 erating vast amounts of heat energy. The extremely fast release of
 a very large amount of energy in a relatively small volume causes
 the temperature to rise to tens of millions of degrees. The result-
 ing rapid expansion and vaporization of the bomb material causes a
 powerful explosion.
--- DB 1.39/004487
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