Multipulse sequences for explosives detection by NQR under conditions of magnetoacoustic and piezoelectric ringing

Abstract

A number of methods for cancelling magnetoacoustic and piezoelectric ringing signals in the spectroscopy of the nuclear quadrupole resonance are presented. The suggested methods include using the sequence (q~0)~-(z-~p~-2z'-q~v-2"r-~o_,-2z-~p_v-z) . anda multipulse analog of the twopulse Hahn sequence with the first pulse replaced by a short steady-state sequence. Another method presented is the method of orthogonal effective fields for a fast saturation of the quadrupole spin system which can be used for subtracting the magnetoacoustic and piezoelectric components from the signal. The suggested methods can be used for the practi~:al purposes of detecting explosive substances and narcotics.

14N-NQR based device for detection of explosives in landmines

“…Besides the aforementioned SLSE pulse sequence, which requires that the preparatory pulse is phase shifted by 90°with respect to the following it train of pulses, more complex phase manipulation schemes have also been used in a multi-pulse NQR spectroscopy [23,24]. As it has been shown in [23], using specially designed phase alternate pulse sequences allows reduction of an unwanted spurious piezoelectric signals which would otherwise conceal the NQR signals from a landmine completely. Usually these piezoelectric signals originate from a silica present in a soil or even from some insulator materials used in an NQR probe head.…”

“…Usually this external noise surpasses the thermal noise of the NQR probe head measure coil so application of low noise preamplifiers helps little or nothing. The articles on NQR detection of landmines published so far focused mostly on physical basics of NQR method [6][7][8][9][10], certain selected hardware problems [11][12][13][14][15][16][17][18][19][20], optimization of pulse sequences for maximum detection sensitivity [21][22][23][24][25] or merely on final results of testing and overall performance of NQR detector systems [26][27][28][29] without giving more detailed description of a complete NQR system that would facilitate design principles of an NQR landmine detector to emerge. Possibly the latter approach is understood given the sensitive nature of the subject.…”

A study of the spin–echo spin-locking effect in multi-pulse sequences in 14N nuclear quadrupole resonance

“…This becomes obvious if we consider the equations for the spin system magnetisation obtained for each of the three sequences [14,18] which vary only by the value of the resonance offset of the effective field of the sequence.…”

“…Therefore, the great interest of researchers in the SLSE effect reflected in numerous publications of both experimental and theoretical nature [1,[7][8][9][10][11][12][13][14][15][16][17][18], is justified.…”