Nuclear weapons

The Fission Bomb

• To prevent premature detonation of a weapon, the nuclear material must be separated into two or more sub critical masses.
• The mechanism which combines these masses is the most important part of the weapon.
• The mechanism must combine the sub critical masses into one supercritical mass fast enough that the mass is fully assembled before there is any chance of the chain reaction blowing the fissile material apart and causing the bomb to fizzle.

The Neutron Generator

• In order to ensure that a chain reaction begins, there has to be free neutrons present in the fissile material when the critical mass is assembled.
• A combination of Po-210 which emits alpha particles, and Beryllium, which emits neutrons when struck by an alpha particle.
• The two substances can be separated by a foil which blocks alpha particles and is designed to break when the bomb is triggered.

The Tamper

• The tamper is a thick layer of heavy material which is designed to produce pressure on the fissionable core as the bomb detonates, allowing more fissions to occur before the materials are blown apart by the energy release.
• The tamper is usually constructed out of U-238 and doubles as a neutron reflector, redirecting neutrons back into the core and increasing the efficiency of the reaction.
• The most effective tamper is Be-9 which actually produces two neutrons when struck by a single neutron.