The analysis of explosive and narcotic substances via 14N Nuclear Quadrupole Resonance (NQR) is a powerful tool for their safe and accurate detection. The transparency of the technique to packaging materials, as well as its non-destructive and highly discriminative nature makes it an ideal technology for security applications. This could potentially make it superior to other commonly used detection methods. However, NQR signals are challenged by a typically low signal-to-noise ratio (SNR) and the presence of piezoelectric interference. These challenges must be overcome to make it a reliable method for detection.
This research presents the development of a fully portable NQR analyser unit designed to rapidly detect the narcotic salt methamphetamine hydrochloride, in volumes up to 10L. Samples were measured under laboratory conditions and a 3-σ confidence detection was achieved in 1 second for a 200g sample. Piezoelectric interference in the acquired NQR signal was effectively removed through engineering of the probe head design. By using a loop-gap sample coil with electrostatic shielding, piezoelectric ringing was suppressed below the detection limit of the system.
These optimisations led to an overall improvement in detection times by approximately two orders of magnitude in comparison to the literature [1]. This, along with the portability of the analyser, highlights the suitability of NQR as a non-invasive detection method for methamphetamine hydrochloride. Such an analyser could find possible applications in the security sector.