General Considerations Concerning the Lattice Structure
Every cycle in a chain reaction has three parts. Let us trace the course of the cycle by following the life of a neutron. Each neutron is created, together with 1 or 2 brothers, by the fission rocess, i. e. the disintegration of a U nucleus into two fragments with the simultaneous emission of 2 to 3 neutrons. This is s the first part of the cycle. The neutron, when created, has a very large energy, about 2 Mev (a velocity of 12,000 miles/sec) and it must be slowed down to thermal velocities (1 mile/sec). This is the second part of the cycle; it occurs in the damper by collisions with relatively light atoms (carbon in the usual H arrangement). The slowing down of the neutrons is necessary because slow neutrons are much more easily absorbed by U than are fast neutrons. The absorption of the neutrons by the U is the third part of the cycle; it causes the U atom by which it is absorbed to undergo fission and thus emit, in its turn, 1 new neutrons.
Unable to display preview. Download preview PDF.