"The problem of nuclear weapon proliferation will not be solved until the
 root cause is attacked. This is the belief that nuclear weapons are desirable
 things to have, whether for use in fighting wars, in deterring and/or
 intimidating adversaries, or only as symbols of technological power or
 political equality with the mighty. Until all these motivations are shown to
 be empty, and until nuclear weapons are outlawed by a world consensus that
 they are too dangerous, politically and militarily counter-productive and
 morally unacceptable, the threat of nuclear proliferation will remain."

p.83, Uranium Enrichment & Nuclear Weapon Proliferation, SIPRI, A. Krass et al.

IMPLOSION ASSEMBLY

The idea here is to have a hollow shell of fissionable material, and compress
it using carefully placed surrounding explosives. By pressuring the material 
into a smaller volume, you increase the density. By doing so, you increase the
probability of a neutron split over neutron loss. You need a precise spherical
shock wave for compression.

The collapsed core is then irradiated with external neutrons to start fission.
The number of nuclei fissioning during later generations is proportional to
how many nuclei you have fissioning initially. This depends on the initial
neutron flux.

Fusion Boosting

At the centre of the core you can have solid Li6D. Some time before detonation
you could also inject the core with T gas, from some exterior device. The idea
is to achieve a fusion reaction in the central pit.

During implosion, the core gains a high enough temperature and
pressure for fusion reactions to occur. The synergy between fusion and fission
reactions greatly improves chain reaction efficiency. Neutrons released from
fusion have much higher energies than those released via fission processes.
When these ultra fast neutrons hit U-235 nuclei, the splitting releases more
neutrons than when U-235 are hit with fission neutrons. The chain reaction
multiplies rapidly, leading to higher temperatures, and more fusion. The
ultimate result is more U-235 splitting than you would have without the
boost.

The shell may be made of U-235 or Pu-239. The first Chinese test employed
a U-235 shell.

Another technique is to introduce a tamper of some sort, which is another shell
surrounding the fissionable material. This shell is usually made of 
Beryllium or U-238. It's purpose is to reflect escaping neutrons back into
the reaction. This has the effect of reducing the amount of fissionable
material needed for a reaction.

The Fat Man bomb used a hollow core, but present day weapons might employ a
solid (subcritical) core of fissile material. The density increase in a solid
core reduces the amount of critical mass required for a chain reaction. This
is because the reaction cross section is substantially increased.

Core Levitation

To increase the impact of the tamper on the fissionable shell, you can
levitate the shell. You leave an air gap between the two materials. This
has the effect of increasing momentum transfer, and hence facilitating
implosion. According to Ted Taylor, in John McPhee's book (see Refs):

"[Taylor] said there was something about the structure of implosion
bombs that he had not gone into, and that he could not go into, which
contributed greatly to their yield... 'All I can say is this: They
had known all along that the way to get more energy into the middle was
to hit the core harder. When you hammer a nail, what do you do? Do you
put the hammer on the nail and push?'"


============================================================================

     [1]  Uranium Detonator
          -----------------

              Comprised of 2 parts.  Larger mass is spherical and concave.
              Smaller mass is precisely the size and shape of the `missing'
              section of the larger mass.  Upon detonation of conventional
              explosive, the smaller mass is violently injected and welded
              to the larger mass.  Supercritical mass is reached, chain
              reaction follows in one millionth of a second.

     [2]  Plutonium Detonator
          -------------------

              Comprised of 32 individual 45-degree pie-shaped sections of
              Plutonium surrounding a Beryllium/Polonium mixture.  These 32
              sections together form a sphere.  All of these sections must
              have the precisely equal mass (and shape) of the others.  The
              shape of the detonator resembles a soccerball.  Upon detonation
              of conventional explosives, all 32 sections must merge with the
              B/P mixture within 1 ten-millionths of a second.

 ____________________________________________________________________________

                                  - Diagram -
                                 -------------
 ____________________________________________________________________________
                                       |
            [Uranium Detonator]        |         [Plutonium Detonator]
 ______________________________________|_____________________________________
                _____                  |
               |    :|                 |               . [2] .
               |    :|                 |           . ~   \_/   ~ .
               | [2]:|                 |        ..        .        ..
               |    :|                 |      [2]|        .        |[2]
               |   .:|                 |     . ~~~ .      .      . ~~~ .
               `...::'                 |    .        .    .    .        .
               _ ~~~ _                 |   .           .  ~  .           .
            . `|     |':..             | [2]\.  .  .  .  [1]  .  .  .  ./[2]
         .     |     | `:::.           |   ./          . ~~~ .          \.
               |     |   `:::          |   .         .    :    .         .
       .       |     |    ::::         |    .      .      .      .      .
               | [1] |    ::|::        |     . ___        .        ___ .
      .        `.   .'   ,::||:        |      [2]|        .        |[2]
                 ~~~     ::|||:        |        .'        _        `.
       ..        [2]   .::|||:'        |           .     / \     .
        ::...       ..::||||:'         |              ~ -[2]- ~
         :::::::::::::||||::'          |
          ``::::||||||||:''            |
              ``:::::''                |
                                       |
                                       |
                                       |
                                       |
       [1] = Collision Point           |      [1] = Collision Point
       [2] - Uranium Section(s)        |      [2] = Plutonium Section(s)
                                       |
                                       |
 ______________________________________|_____________________________________
============================================================================


                        - Diagram for Plutonium Bomb -
                       --------------------------------
                       [Gravity Bomb - Implosion Model]
                       --------------------------------
                        -> Cutaway Sections Visible <-



============================================================================



                                      /\
                                     /  \ <---------------------------[1]
                                    /    \
                  _________________/______\_________________
                 | :      ||:      ~      ~               : |
     [2]-------> | :      ||:                             : |
                 | :      ||:                             : |
                 | :      ||:                             : |
                 | :      ||:                             : |
                 | :      ||:                             : |
                 | :      ||:                             : |
                 | :      ||:                             : |
                 | :      ||:                             : |
                 | :      ||:                             : |
                 | :      ||:                             : |
                 | :      ||:                             : |
                 | :______||:_____________________________: |
                 |/_______||/______________________________\|
                  \       ~\       | :          |:|         /
                   \       |\      | :          |:|        /
                    \      | \     | :__________|:|       /
                     \     |:_\    | :__________\:|      /
                      \    |___\   |______________|     /
                       \  |     \ |~               \   /
                        \|_______\|_________________\_/
                        |_____________________________|
                        /                             \
                       /                               \
                      /                                 \
                     /          _______________          \
                    /       ___/               \___       \
                   /____ __/                       \__ ____\
     [3]_______________________________               \ ___|
                   / __/               \               \__ \
                  / /                  \/                 \ \
                 / /              ___________              \ \
                / /            __/___________\__            \ \
              ./ /__  ___     /=================\     ___  __\ \.
     [4]-------> ___||___|====|[[[[[|||||||]]]]]|====|___||___ <------[4]
            /  /              |=o=o=o=o=o=o=o=o=| <-------------------[5]
           .' /                \_______ _______/                \ `.
           :  |___                    |*|                    ___|  :
          .'  |   \_________________  |*|  _________________/   |  `.
          :   |   ___________   ___ \ |*| / ___   ___________   |   :
          :   |__/           \ /   \_\\*//_/   \ /           \__|   :
          :   |______________:|:____:: **::****:|:********\ <---------[6]
         .'  /:|||||||||||||'`|;..:::::::::::..;|'`|||||||*|||||:\  `.
     [7]----------> ||||||' .:::;~|~~~___~~~|~;:::. `|||||*|| <-------[7]
         :   |:|||||||||' .::'\ ..:::::::::::.. /`::. `|||*|||||:|   :
         :   |:|||||||' .::' .:::''~~     ~~``:::. `::. `|\***\|:|   :
         :   |:|||||' .::\ .::''\ |   [9]   | /``::: /::. `|||*|:|   :
     [8]------------>::' .::'    \|_________|/    `::: `::. `|* <-----[6]
         `.  \:||' .::' ::'\ [9] .     .     . [9] /::: `::.  *|:/  .'
          :   \:' :::'.::'  \  .               .  /  `::.`::: *:/   :
          :    | .::'.::'____\    [10] . [10]    /____`::.`::.*|    :
          :    | :::~:::     |       . . .       |     :::~:::*|    :
          :    | ::: ::  [9] | .   . ..:.. .   . | [9]  :: :::*|    :
          :    \ ::: ::      |       . :\_____________________________[11]
          `.    \`:: ::: ____|     .   .   .     |____ ::: ::'/    .'
           :     \:;~`::.    / .  [10]   [10]  . \    .::'~::/     :
           `.     \:. `::.  /    .     .     .    \  .::' .:/     .'
            :      \:. `:::/ [9]   _________   [9] \:::' .:/      :
            `.      \::. `:::.   /|         |\   .:::' .::/      .'
             :       ~~\:/ `:::./ |   [9]   | \.:::' \:/~~       :
             `:=========\::. `::::...     ...::::' .::/=========:'
              `:         ~\::./ ```:::::::::''' \.::/~         :'
               `.          ~~~~~~\|   ~~~   |/~~~~~~          .'
                `.                \:::...:::/                .'
                 `.                ~~~~~~~~~                .'
                  `.                                       .'
                   `:.                                   .:'
                    `::.                               .::'
                      `::..                         ..::'
                        `:::..                   ..:::'
                          `::::::...        ..::::::'
    [12]------------------> `:____:::::::::::____:' <-----------------[12]
                              ```::::_____::::'''
                                     ~~~~~






============================================================================


                              - Diagram Outline -
                             ---------------------

                        [1] - Tail Cone
                        [2] - Stabilizing Tail Fins
                        [3] - Air Pressure Detonator
                        [4] - Air Inlet Tube(s)
                        [5] - Altimeter/Pressure Sensors
                        [6] - Electronic Conduits & Fusing Circuits
                        [7] - Lead Shield Container
                        [8] - Neutron Deflector (U-238)
                        [9] - Conventional Explosive Charge(s)
                       [10] - Plutonium (Pu-239)
                       [11] - Receptacle for Beryllium/Polonium mixture
                              to facilitate atomic detonation reaction.
                       [12] - Fuses (inserted to arm bomb)




============================================================================

1994
