NQR Imaging

Abstract

Abstract A rotating-frame NQR imaging (ᵨNQRI) procedure based on pure NQR is reported. The technique is suitable for powdery or crystalline solid materials containing quadrupole nuclei. The spatial information is encoded by gradients of the radio frequency amplitude of the excitation pulse. A special deconvolution procedure has been developed for the analysis of the spatial information encoded in the pseudo-FID of the NQR signal in the case of powder geometry. The technique is applicable to rotationally symmetric as well as to asymmetric electric field gradient tensors. The RF gradients are suitably produced by surface coils. The prominent advantage of surface-coil NQR is that objects larger than the coil diameter can be investigated. The imaging procedure then provides depth resolution in a range of the order of the coil radius. The technique is particularly suitable for the detection of gradients of physical parameters influencing the NQR line shift and of spatial distributions of the chemical composition. Examples are stress or temperature gradients. Twodimensional images have been produced by rotating the sample step by step. For each orientation a profile across the sample is evaluated as the projection on the direction of the radio-frequency gradient. A projection-reconstruction formalism then permits the rendering of two-dimensional NQR images.