John A. S. Smith

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Nuclear quadrupole resonance (NQR) offers an unequivocal method of detecting and identifying land mines. Unfortunately, the practical use of NQR is restricted by the low signal-to-noise ratio (SNR), and the means to improve the SNR are vital to enable a rapid, reliable, and convenient system. In this paper, an approximate maximum-likelihood detector (AML)(More)
—Nuclear quadrupole resonance (NQR) is a radio-frequency technique that can be used to detect the presence of quadrupolar nuclei, such as the 14 N nucleus prevalent in many explosives and narcotics. In a typical application, one observes trains of decaying NQR echoes, in which the decay is governed by the spin echo decay time(s) of the resonant line(s). In(More)
Nuclear quadrupole resonance (NQR) is a solid-state radio frequency (RF) spectroscopic technique, allowing the detection of compounds containing quadrupolar nuclei, a requirement fulfilled by many high explosives and narcotics. The practical use of NQR is restricted by the inherently low signal-to-noise ratio (SNR) of the observed signals, a problem that is(More)
Nuclear quadrupole resonance (NQR) is a radio frequency (RF) technique that detects compounds in the solid state and is able to distinguish between different polymorphic forms of certain compounds. For example, a typical sample of trinitrotoluene (TNT) will contain at least two polymorphic forms with rather different NQR properties. In this paper, we(More)
Nuclear quadrupole resonance (NQR) is a radio-frequency (RF) spectroscopic technique, able to detect the presence of many high explosives and narcotics. In practice, the weak NQR signal is often corrupted by strong RF interference (RFI); therefore, various multichannel detection algorithms have recently been proposed for NQR. However, these algorithms allow(More)
In this work, we present a novel method for non-invasive identification of liquids, for instance to allow for the detection of liquid explosives at airports or border controls. The approach is based on a nuclear magnetic resonance technique with an inhomogeneous magnetic field, forming estimates of the liquid's spin-spin relaxation time, T<inf>2</inf>, and(More)