Doctor of Philosophy
School of Physics
The capability to accurately and safely identify security sensitive substances is a tool of paramount importance in defence and security industries all over the world. Nuclear Quadrupole Resonance (NQR) is a radio frequency (RF) spectroscopic technique that probes the nuclear spin states of a material and is uniquely felicitous to the detection of solid-state security sensitive substances. This is because the technique does not demand any sample preparation or direct contact with the target substance. It is a highly specific detection method due to the sensitivity of quadrupolar resonances to the electronic environment surrounding the target nucleus. It also allows for bulk measurements of materials as the magnetic field pulses used to excite the target nucleus are transparent to non-conductive materials. In contrast to its close phenomenological counterpart Nuclear Magnetic Resonance (NMR), a large external magnetic field is not required, making NQR spectrometers suitable for applications in the field.
The research within this thesis focuses on assessing and improving NQR as a detection method for security sensitive substances through experiments on an array of custom built NQR spectrometers. When applying NQR in the field, it is challenged by a characteristically low sensitivity to standard pulse sequences as well as being susceptible to sources of noise and interference. As a result, the work in this thesis is primarily committed to maximising the signal-to-noise ratio (SNR) per unit time and suppressing piezoelectric interference for a range of oxidisers and narcotic salts. In particular, these materials are sodium nitrite, potassium nitrate, methamphetamine hydrochloride and cocaine hydrochloride. The NQR of MDMA hydrochloride and heroin hydrochloride monohydrate is also investigated.
Robertson, Lewis, Practical aspects of nuclear quadrupole resonance as a method for the detection of security sensitive substances, Doctor of Philosophy thesis, School of Physics, University of Wollongong, 2023. https://ro.uow.edu.au/theses1/1736
FoR codes (2008)
0202 ATOMIC, MOLECULAR, NUCLEAR, PARTICLE AND PLASMA PHYSICS, 0203 CLASSICAL PHYSICS, 0204 CONDENSED MATTER PHYSICS, 0206 QUANTUM PHYSICS
Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.