Three-Frequency Composite Multipulse Nuclear Quadrupole Resonance Technique for Explosive Detection

New method of multifrequency nuclear quadrupole resonance (NQR) for the explosive detection has been proposed. This technique consists of application of the series of composite excitation circles, each consisting of two or three successive pulses of different frequencies. In this work, we study in detail the multipulse sequence consisting of n excitation sets, each set consists of three pulses. The first pulse is applied with frequency nu (-), the second pulse with frequency nu (0), and the third pulse with frequency nu (-), but with a shifted phase. The NQR signal is detected at the frequency nu (+). The maximal amplitude of the detected signal is obtained by tuning the pulse parameters at frequencies nu (-) and nu (0). We have shown that the phase of the NQR signal at the frequency nu (+) second part of the composite pulse with the frequency nu (0) the signals with different phases to suppress the spurious signals. The method could be used for increasing the NQR signal, avoiding the spurious signals and improving the reliability of NQR detection. Possible applications of the method for the explosive detection are also discussed.