Density measurement of particleboard, veneer and wood specimens by narrow beam gamma absorption technique

This paper presents gamma absorption methods for measuring density distributions of different types of wood products. Local density distributions of particleboard and wood specimens (thickness 20-70 mm) can be measured by using 241 Am (59.5 keV) gamma-absorption technique. 55 Fe (5.9 keV) gamma-absorption technique can be used for the measurement of density distributions of veneer sheets (thickness 1-3 mm). An automated equipment have been constructed and modified for each application. The equipment detects and scans the specimens, which are placed on the gamma-absorption gauge. The analysis report with images and numerical values are processed by PC. The measured data values can be easily transferred to other programs for further analysis. The correlations between the densities measured by gamma method and gravimetrically measured densities were excellent : correlation coefficient r was over 0.9 in each calibration test and the standard deviations varied between 5-20 kg/m 3 . By using the gamma absorption method, it is possible to estimate the dry wood density of a wood product with good accuracy without drying the specimen, when the moisture content is low and the variation of the moisture content is limited to a few per cent.