Multigroup Coupled Neutron-Gamma Cross-Section Library for Deterministic and Monte Carlo Borehole-Logging Analysis

A special-purpose multigroup cross-section library optimized for nuclides and reactions arising in nuclear oil well logging was prepared for use in deterministic and Monte Carlo transport codes. The library is based on the recent ENDF/B-VI.8 evaluation, which includes among others improved oxygen and chlorine cross sections. A 175-neutron and 45-gamma-ray energy group structure was selected as a way to take into account the requirements of oil well-logging applications. This library is expected to improve the prediction of the neutron and gamma spectra at the detector positions of the logging tool. For the Monte Carlo codes the library can be useful in particular in calculations requiring multigroup cross sections, like adjoint or MIDWAY methods. Furthermore, comparison of deterministic and Monte Carlo calculations using the same or similar cross sections can reveal the uncertainty linked to the computational method and model. The use of the library for the interpretation of the carbon/oxygen neutron logging measurements in boreholes was studied. Preparation and testing of this library, which is available from the Organisation for Economic Co-operation and Development/Nuclear Energy Agency Data Bank, is described.