PROTON SPIN-LATTICE RELAXATION IN WOOD - T-1 RELATED TO LOCAL SPECIFIC-GRAVITY USING A FAST-EXCHANGE MODEL

The spin-lattice relaxation and cross relaxation of western redcedar s apwood (moisture contents 216 to 15%) and western hemlock sapwood (moi sture contents 144 to 15%) were investigated using proton magnetic res onance, Below the fiber saturation point (FSP), solid wood and cell-wa ll water were found to have the same T-1 indicating a fast exchange of proton magnetization between these two environments, Above the FSP, m ultiexponential T-1 decay was observed, A one-dimensional profile acro ss the growth rings showed that the multiple components of spin-lattic e relaxation in wood were due to variations in local specific gravity, Within a small volume, a single T-1 was observed for protons in lumen water, cell-wail water, and solid wood, The mixing of proton reservoi rs was attributed to water diffusion between the lumen and cell wall, and cross relaxation between the protons in the cell-wall water and th e solid wood. This cross-relaxation time was found to be a few millise conds, which is fast on the T-1 time scale of tens of milliseconds. A fast-magnetization-exchange model which related T-1 values to local sp ecific gravity was verified for protons in all environments in wood, U sing this model, the distribution of local specific gravity was derive d for the western red-cedar and hemlock samples. (C) 1996 Academic Pre ss, Inc.