Combined neutron and X-ray imaging to estimate moisture-content distribution in wood

Abstract The high sensitivity of neutrons to hydrogen, together with the key role of moisture in wood utilisation, makes wood–water interactions a central topic in neutron imaging studies. However, neutron imaging alone does not enable direct quantification of dry-weight-based moisture content (MC), thereby limiting its application in moisture analysis. This study presents a combined neutron and X-ray imaging method to monitor temporal changes in wood moisture with detailed anatomical resolution. Scots pine sapwood specimens with initial MCs ranging from green state to approximately 24 %, 12 %, and 0 % were subjected to unidirectional drying or wetting under controlled relative humidity decreasing from about 85 % to 30 % at 60 °C. Eight specimens were imaged simultaneously, and image-registration techniques were applied to compensate for shrinkage and swelling during moisture changes. Wood was modelled as discrete layers of compact timber, water, and void space. While neutron imaging provided high sensitivity to water distribution, combining both imaging modalities enabled estimation of MC and improved anatomical visualisation. The method allows investigation of wood–water interactions across entire cross-sections down to individual growth-ring features. By enabling detailed tracking of moisture dynamics under controlled climatic conditions, the approach supports improved understanding of wood drying behaviour and moisture-related material performance.