Local densitometry of wood by gamma back-scattering

Abstract

Density of wood is one of the major material property. The article presents a simple, quick and precise local density measurement based on the gamma back-scattering technique. The equipment works with an 1GBq activity Am-241 ring source. Linear relationship was found between the back-scattered gamma ray intensity and the density of wood within the density range of 350–900 kg/m3. Using this technique non-contact local densitometry is possible. If the specimen thickness is less than 70 mm (saturation thickness) the specimen thickness must be well known, because in this thickness range the back-scattered gamma ray intensity depends on the thickness. A calibration curve should be determined for all thicknesses below 70 mm. Another limitation is that the equipment contains radioactive material. The user needs a special licence and permission from the authorities responsible for radioactive materials.