A PULSED NEUTRON SOURCE TECHNIQUE

For a measurement of the diffusion constant D from the decay of the fundamental mode only, optimal dimensions of the pile are given, leading to a fast decay of the higher modes. Another method is discussed which makes use also of higher modes. Evaluation formulas and optimal pile dimensions for this method are derived. The amplitudes of the normal modes are calculated for different initial distributions of the neutrons by means of the Fermi age theory. The error introduced using Fermi age theory was fixed moderator atoms for the slowing down process down to thermal energy is estimated. In one instance, for a simple initial distribution of thermal neutrons, the neutron density was calculated as a function of space and time. The data obtained were used to check the accuracy of some approximate evaluation formulas derived here. (auth