Transmission measurement of porosity with a neutron generator in geophysics applications

Fast neutron transmission measurements, based on a stationary neutron gener ator, were performed to determine the volume porosity of a sample in a mode l experiment. The free volume in the mock-up, consisting of a cylindrical h older containing glass rods and sometimes: even sand, was determined from m easurements of the transmitted fast neutron flux in dry and flooded (with w ater) condition. In order to extract a quantitative measure of the free vol ume from the measurement, the neutron attenuation through the sample was mo delled by the first Eight approximation as well as with more advanced MCNP calculations. The experimental results show good agreement with results of the advanced Monte-Carlo calculations within the estimated error. Porositie s of samples that were evaluated from the measurement using MCNP calculatio ns for calibration show an error between 3 and 14% in comparison with the t rue (known) values. (C) 2001 Elsevier Science B.V. All rights reserved.