G. V. Mozzhukhin

Size Effect in 14N Nuclear Quadrupole Resonance Spectroscopy

The influence of the size effect of the crystallites in powders on the form and width of spectral lines, on the spin-spin and spin-lattice relaxation parameters of the nuclear quadrupole resonance (NQR) of 14N nuclei in sodium nitrite was studied. It was established that a decrease of the average crystallite size produces the widening of the NQR lines and the shortening of the relaxation times in the direct method of NQR detection. It was supposed that these are the results of the spin-spin diffusion process. A multi-exponential inversion of the decays of the longitudinal and transverse components of the nuclear magnetization was used to obtain the distribution of relaxation times.

Novel approaches in nuclear magnetic/quadrupole resonance techniques for explosives detection

Nuclear Quadrupole Resonance (NQR) and Nuclear Magnetic Resonance (NMR) are very prospective methods of the bulk detection of explosives and illicit substances. Both methods are based on use of apparatus, which are very similar technically and in some cases could be applied simultaneously. We report our experimental works on NQR/NMR techniques for explosives detection. In addition of classical single-frequency NMR/NQR we also explored a potential of double resonance (NMR/NQR) and multifrequency NQR approaches as well as magnetic resonance imaging (MRI) techniques. Multifrequency (two/three) NQR technique involves various (two or three) transitions in the three energy level system of 14N nuclei. It is shown that this kind of NQR technique allows filtering spurious signal after radiofrequency pulses and increases the sensitivity of NQR detection. On the other hand, various liquids can be detected using NMR. We shown that reliable discrimination among extended set of liquids reveal a need in use of additional NMR parameters or complimentary techniques. It is demonstrated that MRI is also feasible method for detection of explosive/illicit liquids.

Secondary signals in two-frequency nuclear quadrupole resonance on 14N nuclei with I = 1

Our experimental and theoretical studies show that using two-frequency excitation of (14)N nuclei it is possible to observe secondary NQR signals at one of the three possible transitions due to irradiation of another adjacent transition. As a result of the pulse sequence applied to the adjacent transition the spin-echo signals on the detected transition are observed after essential time interval from the initial single pulse on this frequency. Experiments have been performed on the (14)N nuclei in the sodium nitrite (NaNO(2)) and the military explosive hexahydro-1,3,5-trinitro-s-triazine C(3)H(6)N(6)O(6) (RDX).

Synthesis & characterization of tetrahedrite compounds for thermoelectric applications

Thermoelectric materials have attracted much attention due to their potential applications in conversion of heat into electrical power or vice versa to cool the heat-generating elements using electrical power. Tetrahedrite is copper antimony sulfosalt mineral with the formula of Cu₁₂Sb₄S₁₃, where Cu could be partially replaced by another 3d (Mn, Ag, Al, Cr, Zn, Fe) or other (4d,5d) metal. This group of compounds is very prospective for large-scale thermoelectric applications. The compounds could be represented by common formula of the compound Cu_10-xM_2-xSb_4-yQ_yS_13-zTz. M=Au, Mn, Ag, Al, Cr, Zn, Fe; Q=As, Sn, Zn, Pb; Z=O, Se. The procedure of solid state reaction for tetrahedrite powder samples of various composition have been developed. The single phase tetrahedrite samples of Cu₁₂Sb₂As₂S₁₃, Cu_11.8Au_0.2Sb₄S₁₃, and Cu₁₀Fe₂Sb₄S₁₃ have been synthesized as proved by XRD. Characterization of their magnetic properties by VSM PPMS have been done.

Signal processing in NMR/NQR detection on the base of pattern signal

The proposed method allows defining the nuclear magnetic/quadrupole resonance (NMR/NQR) signal with use the previously famous parameters of the signal for detecting substance. The result of the detection this signal is the detection and identification of the substance. The method is based on the convolution of the pattern signal and detecting signal after continuous wavelet transformation and estimation of mutual coherency. The comparison of the threshold values of the mutual coherency function wit and without signal shows the presence of the signal of detecting substance.

On Question of Possibilities of NMR in Weak Magnetic Fields for Detection of Illicit Liquids

The method of the detection and identification of different liquids on the basis of registration of NMR in the Earth magnetic field has been discussed. Some general aspects of the problem are considered to illustrate the near-term outlooks. In particular, the polarization of nuclei with an alternating magnetic field \(B^{{\ast}}(B^{{\ast}}\gg B_{0})\) at a very low frequency F (but \(F \gg \frac{1} {T_{1}}\), where T 1 is the spin-lattice relaxation time) has been investigated. The study is directed to the development of the application of industrial power (50 Hz) for the nuclear polarization. The question of the optimization of the energy consumption during the pre-polarization is also considered. The possibilities of the method are illustrated by the observation of NMR signals from liquids with the external sample location and in aluminum closed cans.

Cross-Relaxation Enhanced NQR of Ammonium Nitrate in Low Magnetic Field

Nuclear quadrupole resonance (NQR) with use of pulses of low magnetic field has been studied. The technique is based on the matching of proton frequency (ν L) to one of the NQR frequencies (ν 0, ν + or ν −) for the period of application of pulse magnetic field. Theoretical approach to analyse the NQR experiments in pulse magnetic fields is outlined. In this work the NQR on ammonium nitrate (AN) sample for specific case of ν L = ν 0 have been studied. It has been shown that the technique provides essential shortening the effective spin-lattice relaxation time and can be applied for the detection of explosive materials.