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 designed to develop an automated defect-detection and timber-classifying system for 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 linear attenuation coefficients resulting from scanning along the radial and tangential 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 12.5 cm wide by 20 cm in length, and the moisture content of the samples ranged 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 coefficient was a good indicator ofthe presence of knots in the samples. The results showed a high degree of sensitivity of the attenuation coefficient 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 tangential directions of irradiation.