Nuclear quadrupole resonance

About: Nuclear quadrupole resonance is a research topic. Over the lifetime, 3531 publications have been published within this topic receiving 38801 citations. The topic is also known as: Nuclear quadrupole resonance spectroscopy & NQR.

Signal processing for NQR discrimination of buried land mines

Abstract: Nuclear quadrupole resonance (NQR) is a technique that discriminates mines from clutter by exploiting unique properties of explosives, rather than the attributes of the mine that exist in many forms of anthropic clutter. After exciting the explosive with a properly designed electromagnetic-induction (EMI) system, one attempts to sense late-time spin echoes, which are characterized by radiation at particular frequencies. It is this narrow-band radiation that indicates the presence of explosives, since this effect is not seen in most clutter, both natural and anthropic. However, this problem is complicated by several issues. First, the late-time radiation if often very weak, particularly for TNT, and therefore the signal-to-noise ratio must be high for extracting the NQR response. Further, the frequency at which the explosive radiates is often a strong function of the background environment, and therefore in practice the NQR radiation frequency is not known a priori. Finally, at the frequencies of interest, there is a significant amount of background radiation, which induces radio frequency interference (RFI). In this paper we discuss several signal processing tools we have developed to enhance the utility of NQR explosives detection. In particular, with regard to the RFI, we exposure least-mean-squares algorithms which have proven well suited to extracting background interference. Algorithm performance is assessed through consideration of actual measured data. With regard to the detection of the NQR electromagnetic echo, we consider a Bayesian discrimination algorithm. The performance of the Bayesian algorithm is presented, again using measured NQR data.

Zeeman Effect of Nuclear Quadrupole Resonance Spectrum in Cyanuryl Chloride

Abstract: A study on the Zeeman effect of Cl 35 nuclear quadrupole resonance spectrum was carried out on a single crystal of cyanuryl chloride. Three distinct q -tensors were found in this crystal, two of them being equivalent. The directions of the principal axes were determined within the accuracy of 1° . It was concluded that in the crystal all molecules are disposed parallel (or antiparallel) to one another and three C–Cl bonds of a molecule are on a plane, making an angle 120° with one another, one of them being not equivalent to the other two. A large asymmetry parameter, 0.26, was obtained. From the coupling constant and the asymmetry parameter, the double bond character and the ionic character of C–Cl bonds were estimated to be 10% and 17%, respectively. The large double bond character was considered to be associated with the large electronegativity of nitrogen atoms in the ring.