Neutron Moisture Gauge for Roofing Surveys Experiment and Simulation

Abstract

Moisture content within roofing materials can be measured by the use of a gauge incorporating a neutron source and detector with associated electronics. The response to the water content in the roofing materials is proportional to the backscatter neutron flux. Such a prototype neutron moisture gauge has been built and response characterized for various geometric parameters and two neutron source strengths. Ultimately, moisture gauge response is documented for a range of known water densities in the insulation material of several laboratory replicas of roofing sections. Computer simulation of the neutron moisture gauge has also been carried out for the two different roofing section replicas using a two energy group diffusion theory model. Detector response, computer for a range of water content in the roofing insulation, exhibits a steeper trend with increasing water content than actually observed in experimental results. Analysis shows that the two-group diffusion equations are sensitive to small changes in arguments. These arguments are subject to errors in ascertaining both neutron cross sections and molecular compositions of roofing materials. Although a crude representation of a complex system, the diffusion theory adequately correlated with experimental response data and verified moisture gauge design parameters.