Abstract: A nuclear magnetic resonance sensing apparatus, including a magnet for inducing a static magnetic field within materials to be analyzed. The magnetic field is substantially coaxial with a longitudinal axis of the apparatus. The magnetic field is polarized substantially perpendicularly to the longitudinal axis and is symmetric about the axis. The static magnetic field has a maximum longitudinal gradient which is inversely related to a speed of motion of the apparatus along the longitudinal axis through the materials to be analyzed. The apparatus includes a transmitter for generating a radio frequency magnetic field in the materials for exciting nuclei in the materials. The radio frequency magnetic field is substantially orthogonal to the static magnetic field. The apparatus includes a receiver for detecting nuclear magnetic resonance signals from the excited nuclei in the materials. In a preferred embodiment, the magnet comprise magnetized cylinders stacked along the longitudinal axis.