The use of linear attenuation coefficients of gamma radiation for detecting knots in Pinus radiata

This paper reports on the preliminary results of a research project designe d to develop an automated defect-detection and timber-classifying system fo r Pinus radiata (D. Don), by using a collimated gamma-ray photon beam from a 59.5 keV (Am241)energy source. The analysis was made by measuring the lin ear attenuation coefficients resulting from scanning along the radial and t angential directions of six specimens of Pinus radiata, with densities that ranged from 430 g/cm(3) to 620 g/cm(3). The samples were 4.2 cm thick by 1 2.5 cm wide by 20 cm in length, and the moisture content of the samples ran ged from 8 to 12 percent. The samples included sound knots that varied from 2 cm to 5 cm in diameter. It was established that the linear attenuation c oefficient was a good indicator of the presence of knots in the samples. Th e results showed a high degree of sensitivity of the attenuation coefficien t to variations in the density of the material, based on the high degree of correlation that was obtained (r(2) = 0.95), both in the radial and tangen tial directions of irradiation.