The neutron absorption cross section (Sigma) of a sample is a measure of the moderating power of the sample in response to its bombardment by neutrons. This physical property is measured automatically by the Geochemical 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 Sigma of lithologies commonly drilled in the Ocean Drilling Program (ODP) for both lithological characterization and the calibration of the GLT measurements. From Hole 896A 10 samples of basaltic basement were selected for Sigma measurements. For these samples Sigma shows only a small range of variation in response to the nearly constant chemistry of the basement, with an average of 0.00599 cm2/g, and standard deviation of 0.00027 cm2/g. Over the depth interval from which the core samples were taken (195–355 mbsf) the increase in Sigma observed with depth is a direct result of increasing iron and titanium in the basalts.

Date of initial receipt: 8 August 1994
Date of acceptance: 14 March 1995

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