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The Basics - Level 2

The Basics - Level 2. The fission process. Nucleus of U-235 or Pu-329 captures a neutron - U-236, Pu-240 nucleus formed. U-236, Pu-240 very unstable, rapidly split into two (fission). Neutrons and a large burst of energy are emitted.

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The Basics - Level 2

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  1. The Basics -Level 2

  2. The fission process • Nucleus of U-235 or Pu-329 captures a neutron - U-236, Pu-240 nucleus formed. • U-236, Pu-240 very unstable, rapidly split into two (fission). • Neutrons and a large burst of energy are emitted. • Complete fissioning of 1 gram of U-235 releases 23,000 kilowatt-hours of heat.

  3. Critical mass • Each nucleus undergoing fission must produce a neutron that splits another nucleus. • Critical mass - the minimum mass of fissile material that can sustain a nuclear fission chain reaction. • Sphere is optimum shape.

  4. Nuclear explosions • If critical mass is exceeded more neutrons are produced with each successive generation of fission. • Nuclear explosions occur at super-critical masses, when the number of neutrons increases rapidly and uncontrollably.

  5. Nuclear explosions • Basic weapons contain fissile material less than critical mass. On detonation, density is increased to super-critical - a process referred to as "assembly". • Within half a millionth of a second: • Temperatures - hundreds of millions degrees centigrade, and pressures - millions of atmospheres, build up.

  6. Fusion • Isotopes of hydrogen - deuterium and tritium. • Extremely high temperatures required for reaction to occur. • Require a fission bomb to provide energy to initiate reaction. • Used mainly to ‘boost’ fission bombs - increase fission rate by providing more high energy neutrons.

  7. Detonation techniques Gun technique • Only used with HEU. • Mass of sub-critical HEU fired at another - sum of two masses supercritical. • Simple technique. • Long assembly time. • Hiroshima bomb.

  8. Detonation techniques • Implosion technique • 1/10 the assembly time of the gun technique. • HEU or plutonium can be used. • Fissile core surrounded by conventional high explosives.

  9. Detonation techniques • Implosion technique • Explosives detonate and uniformly compress the core and increase its density, making it super-critical. • Neutrons also fired into fissile material to encourage fission chain reaction.

  10. Main components of nuclear weapons • High quality, high purity conventional high explosives and reliable detonators. • Electronic circuits. • A tamper and neutron reflector. • A core of fissile material. • A neutron source.

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