Correlated sampling added to the specific purpose Monte Carlo code McPNL for neutron lifetime log responses

The special-purpose neutron-lifetime oil well logging simulation code, McPNL, has been rewritten for greater user-friendliness and faster execution. Correlated sampling has been added to the code to enable studies of relative changes in the tool response caused by environmental changes. The absolute responses calculated by the code have been benchmarked against laboratory test pit data. The relative responses from correlated sampling are not directly benchmarked, but they are validated using experimental and theoretical results. The correlated sampling scheme has been tested using the addition of p.p.m. levels of boron-10 to a 13% porosity limestone reference formation and showed excellent agreement with the expected change in the thermal capture cross section