Relaxation in a Natural Soil: Comparison of Relaxometric Imaging, T1 – T2 Correlation and Fast-Field Cycling NMR

Longitudinal and transverse relaxation times are used to characterise the pore system of a natural Kaldenkirchen sandy loam. Here we present new results obtained by relaxometric imaging (MEMS) and two-dimensional T1-T2 correlation relaxometry, and compare these with available T1relaxation time distributions of water obtained by the analysis of fast field cycling relaxometry (FFC) data. The soil shows relatively broad bimodal distribution functions P(T1) and P(T2) with a T1/T2 ratio of about 2:1. The average T1 as well as the spatial distribution, which are obtained from the relaxometric imaging corresponds well to the relaxometric results. From the analysis of the field dependent FFC data at low field including T1 data obtained at high field the basic locally averaged relaxation mechanism is derived from the dispersion curve, i.e. the dependence of the relaxation rate from the magnetic field strength over five orders of magnitudes. From this we conclude that two-dimensional diffusion at locally flat surfaces controls the relaxation, i.e. the shapes of the distribution functions are controlled by surface relaxation.