A Review of Methods for Determining Moisture Content and Density of Wood By Nuclear Radiation Techniques

Moisture content and density are constantly changing parameters in wood and wood products. Because of their strong interaction, separate determination of these parameters has been a problem for researchers. Various nuclear radiation techniques to measure moisture content and density are described and their principles are discussed. Radiation measurement techniques require a source of radiation and a radiation detector to count the number of, or a manifestation of the number of, particles or photons reaching the detector. Common sources of radiation are alpha, beta, and gamma particles and neutron radiation. The two most commonly used detectors for wood density are the Geiger-Miler and the scintillation counters; their operation is described. Literature on this topic is reviewed briefly and summarized. Wood density, especially in thin sections, may be measured with a degree of accuracy by use of beta rays. Because of their great penetrating power, gamma rays are best used to measure density differences associated with decay in large wood cross sections, such as poles and standing trees. Radiation determination of moisture content is best suited for measurements above the fiber saturation point. It is possible to measure both moisture content and density simultaneously by using a combination of radiation techniques or radiation combined with other techniques.

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