Gamma Ray Attenuation by Loblolly Pine Wood: An Investigation of Integral Counting

Within limits, attenuation by wood of Pinus taeda L. by either integral or differential counting was equally satisfactory. Because the former requires simpler equipment and is more adapted to field work, it was further explored. Linear attenuation coefficients were measured for the wood (specific gravity .485 g/cm3) at various moisture contents using an integral narrow beam of gamma photons from a mock iodine-131 source. Half-thickness values and mass attenuation coefficients were also calculated for each moisture content. Results indicate that the wood has a mass attenuation coefficient very similar to that of water, greater than that of concrete or aluminum, and smaller than that of lead or tin. Half-thickness values are about twice as high for oven dry wood as for water. However, at a moisture of 50-60 percent (by volume) wood has a half-value almost identical to that of water. At this moisture content about 6 centimeters of wood between the detector and a point source will reduce the count rate by half.