Year
2008
Abstract
We develop a fully analytic and self-contained description of the amplitude distribution of light pulses in an organic scintillation detector due to a monoenergetic source of fast neutrons. To this end, two classes of problems have to be handled. One is a formula for the light pulse amplitude distribution for the complete life history of neutrons slowing down in a mixture of hydrogen and carbon as a statistical average over all collision sequences that can occur, accounting also for neutron leakage. A complete solution is given in terms of a non-recursive convolution integral expansion with respect to the various possible collision histories. The solution includes the collision probability of neutrons of a given energy. The second is the calculation of this collision probability for the geometry of the detector, in the present case a right cylinder, from analytical expressions. This quantity was taken from Monte-Carlo simulations in all previous work. By calculating the collision probability from transport formulae, the analytical work and the Monte Carlo simulations, which are checked against each other, become completely independent. Recursive formula are derived for the probabilities of arbitrary collision sequences, and quantitative results are given for up to three consecutive collisions of all combinations. These probabilities can be used to determine how to truncate the non-recursive expansion of the full light amplitude distribution in quantitative work. Quantitative results for the light pulse distribution will be given in later work.