METHOD AND APPARATUS FOR IMPROVING THE DETECTION OF NUCLEAR QUADRUPOLE RESONANCE SIGNALS IN COHERENT NOISE

A method for exciting an NQR signal in a substance within a material that may include the substance and detecting the NQR signal in the presence of coherent noise. The method comprises irradiating the material with multiple RF pulses in the form of a complex pulse sequence containing a plurality of blocks. The basis of each block comprises a composite pulse formed by phase cycling a plurality of pulse elements. The method includes receiving a response signal after each composite pulse and processing the response signals to progressively mitigate the effect of coherent noise and to distinguish the existence of an NQR signal if present. The phase cycling comprises generating at least three pulse elements of equal duration but of differing phase to form the composite pulse. In this manner, successive blocks progressively mitigate the effect of coherent noise, and ameliorate the NQR signal if present. An apparatus for performing the method is also described.