Improvement of the MCNP simulated n-gamma spectrometer response function using the new ENDF/B-VI evaluations for thermal neutron capture

An impact of the improved nuclear data library for thermal neutron capture (ENDF/B-VI.8) on the numerically simulated response of the spectrometric n-gamma well logging (sNGL) probe, SO-5-90-SN type, has been investigated. For this aim the MCNP simulations have been done using two kinds of data libraries for radiative capture: the commonly used ENDF/B-VI.2 (ENDF60) and the new ENDF/B-VI. 8 (ACTIA). MCNP simulations concerned the n-gamma benchmark experiment which was performed at the Polish calibration station in Zielona Góra to investigate the influence of chlorine in borehole on the tool readings and thus on the accuracy of quantitative elemental analysis for the main rock elements: Si, Ca and Fe.High quality of the nuclear data for radiative capture in Cl and Al have been of special interest as the ENDF60 library contains an imperfect data for Cl and there is no delay gamma-ray line of energy 1.7791 MeV from thermal neutron capture in Al. The last element is the main construction material for the SO-5-90-SN spectrometer.The advantage of the new ACTIA library over the ENDF60 was shown through the better matching of the experimental and simulated gamma-ray spectra from thermal neutron capture. As a consequence the Si, Ca and Fe rock contents obtained from the MCNP modeling with the use of ACTIA data, fit well their reference values regarded as “true”. The accuracies for the Si, Ca and Fe determination have been improved by about 63%, 35% and 51%, respectively.