Monte Carlo optimization of Tittle's Method for [Sigma][sub a] measurement of geologic samples

The thermal capture cross section [Sigma][sub a], of geologic strata is an essential parameter in borehole logging using neutron tools. The measurement of [Sigma][sub a], can be done by several different methods, the simplest of which was originally described by Tittle and Crawford and more recently adapted and enhanced by Bussian et al. The basic principle is to place the sample in a steady thermal flux and measure the counting rate on a detector located very close to the sample. The measurement system is calibrated using standard samples of known [Sigma][sub a]. Although the measurement is straightforward, optimization of the measurement system has not been carried out and forms the topic of this paper. This paper discusses an experimental system that we have set up to perform measurements for petroleum companies and a study of the optimization of this system using our specific purpose Monte Carlo code, McDNL.