Development of Earth’s Field Nuclear Magnetic Resonance (EFNMR) Technique for Applications in Security Scanning Devices

Abstract

In this work Earth’s field nuclear magnetic resonance (EFNMR) technique for applications in security scanning devices has been presented. The EFNMR setup has been build based on Magritek low-frequency (0–1 MHz) KEA-2 NMR console. Excepting the NMR console, all components are home-made units, which are a first-order gradiometer RF probe, pre-polarization system, magnetic field shimming system, RF shielding box and passive filters. Our measurements have shown that even in very noisy lab conditions the EFNMR signals of small amounts (~5 ml) of liquid samples could be measured. EFNMR measurements of various liquids have been performed and their spin–lattice T₁ and spin–spin T₂ relaxation constants have been obtained. A possibility to detect, at the same time, both fluorine and proton resonance has been shown by EFNMR measurements of trifluoroacetic acid. A good spectral resolution of EFNMR setup has been demonstrated by the spectroscopic measurements of heteronuclear J-coupling of trimethyl phosphate and fluorobenzene. Furthermore, we have shown that the EFNMR measurements of T₁ and T₂ constants as well as heteronuclear J-coupling of liquids enclosed in metallic containers are feasible. Possible applications of the EFNMR technique in security scanners for the detection of illicit and energetic substances are discussed.