Neutron Absorption Cross Section (Sigma) of Basaltic Basement Samples from Hole 896A, Costa Rica Rift

Abstract

The neutron absorption cross section (Σ) of a sample is a measure of the moderating power of the sample in response to its bombardment by neutrons. This phys. property is measured automatically by the Geochem. Logging Tool (GLT), and is required for the subsequent land-based data processing of the GLT logs. This contribution reports part of a project to measure accurately the Σ of lithologies commonly drilled in the Ocean Drilling Program (ODP) for both lithol. characterization and the calibration of the GLT measurements. From Hole 896A 10 samples of basaltic basement were selected for Σ measurements. For these samples Σ shows only a small range of variation in response to the nearly const. chem. of the basement, with an av. of 0.00599 cm2/g, and std. deviation of 0.00027 cm2/g. Over the depth interval from which the core samples were taken (195-355 mbsf) the increase in Σ obsd. with depth is a direct result of increasing iron and titanium in the basalts. [on SciFinder(R)]