Rock neutron parameters: Pt. 2

This paper describes how to calculate the principal thermal neutron parameters of rocks. The parameters of interest are: absorption cross section, diffusion length and diffusion coefficient. These parameters should be calculated for two distinct physical situations: one for a thermal neutron velocity of 2200 m/s and the other for an average over the slow neutron energy spectrum which exists in a given rock. The method of calculation is described using, as an example, the well-known test pits at Houston, Texas which are made from Carthage marble, Indiana limestone and Austin chalk. An additional example is based on Mucharz sandstone which is used in Poland for constructing test pits. The results obtained for the test pits show the importance of having experimental information on the rock matrix absorption cross section. Without this data any calculation of the rock thermal neutron diffusion parameters is almost meaningless, since any trace elements present in the rock matrix but not identified in a routine elemental analysis may give a very significant contribution to the rock absorption cross section and hence to the rest of the thermal neutron diffusion parameters. (author)