The Relationship Between Gamma Ray Absorption and Wood Moisture Content and Density

It is known that a relationship exists between monoenergetic gamma ray attenuation and density. This study was initiated with the objective of determining whether this relationship is sensitive enough to measure gross density variations encountered in wood. These gross density variations are the result of variations in wood specific gravity and moisture content. A scintillation counting system was used to measure the gamma ray attenuation. The source used was one millicurie of lead-210 (radium D), which has a half-life of 22 years and a primary energy peak of 47 Kev. A 6-centimeter-thick octagonal-shaped specimen was used. Yellow-poplar sapwood was used to make the specimens. It was found that if either specific gravity or moisture content is known the other can be determined nondestructively, rapidly, and accurately be measuring gamma ray attenuation through a given thickness. The presence of shrinkage in wood below fiber saturation requires that separate gamma ray absorption models be used above and below fiber saturation. The linear absorption coefficient closely follows the rate of shrinkage from fiber saturation to ovendry.

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