THE DEPENDENCE OF ELEMENTAL YIELD VARIANCE ON DETECTOR TYPE THROUGH MATHEMATICAL-MODELING

The impact of detector choice on the elemental variance in the yields for capture gamma-ray spectrometry is studied assuming identical extrenal environments and neutron source output. The trade-off between lower sensitivity but moderate resolution detectors such as NaI and CsI with the higher sensitivity but lower resolution detectors such as GSO (gadolinium silicate) and BGO (bismuth germanate) is quantitatively assessed. Several common well logging environments are modeled with the Monte-Carlo code MCNP and convolved with detector response maps for each detector type. The elemental standards for the environmental cases are computed and the standard weighted-least-squares fitting procedure is applied. Five elements (H, Si, Ca, Cl and Fe) are assumed present. The variance-covariance matrix from this procedure provides the uncertainty in the elemental yields. Laboratory results obtained using a BGO detector benchmarked the modeling. Copyright © 1990 by The Institute of Electrical and Electronics Engineers, Inc.