System and method for detecting contraband based on nuclear quadrupole resonance.
System and method for detecting contraband based on nuclear quadrupole resonance
The US patent described below proposes a method and system for detecting explosives and narcotics of certain classes by exciting nuclear quadrupole resonance (NQR) in their components containing nuclei with an electric quadrupole moment.
The detection system, the operation of which is based on the use of NQR, includes:
— a sequence controller that issues clock pulses and programming pulses to the system;
— a radio frequency subsystem containing a source of radio frequency oscillations of adjustable frequency for pulsed excitation of NQR at a certain characteristic frequency in the sample of substance being studied. The characteristic frequency of NQR is the frequency at which the interaction of nuclei with a quadrupole moment with the crystal field occurs;
— a detection head subsystem with a distributed radio frequency coil pressed into a flat sheet; this place with the coil is shaped as a volumetric resonator, into which the selected samples of substances are placed for examination. The pulses coming into the coil from the radio frequency subsystem create a uniform electromagnetic field in the volumetric resonator, which affects the substances contained in the sample. The coil simultaneously acts as an element perceiving the NQR signals excited in the sample. These signals form the NQR output signal of the detection head;
— a device for tuning the radio frequency coil to the NQR frequency characteristic of the sample being examined;
— an electrically conductive radio frequency shield surrounding the cavity resonator with the coil and protecting them from the effects of external electromagnetic interference, as well as preventing the magnetic flux from exiting the cavity resonator. The latter, together with the coil and the shield, form a scanner;
— a subsystem for receiving and processing NQR signals, containing: components for receiving output NQR signals from the radio frequency coil; memory for storing NQR signal samples characteristic of explosives and narcotics of certain classes; means for processing the received NQR signals; means for comparing the processed NQR signals with the characteristic signals stored in memory and issuing the resulting output signal;
— a display unit that receives the resulting output signals and selectively reproduces information on the presence or absence of hazardous substances in the sample under study or intermediate information indicating the need for additional sample studies.