Strong off-resonant comb

The chapfer consists of four sections, which are devoted to theoretical and practical issues of the detection of nitrogen-containing substances. Section 2 deals with theoretical aspects of the two most popular multi-pulse sequences multipulse spin-locking—MW-4 and "strong off-resonant comb"—SORC. In spite of the fact that the development of these sequences has enabled a dramatic increase in the sensitivity of NQR methods, until recently a number of theoretical and experimental peculiarities of these sequences have not been studied adequately. The primary issue concerns the sequence SORC, and also behaviour of both sequences in case of close times of spin-lattice and dipolar relaxations, which is especially important for the detection of such a popular explosive as hexogen (RDX). There are also demonstrated some experimental techniques for the detection of some other explosives (PETN and trinitrotoluene (TNT)). 

The application of various multi-pulse methods in NQR requires a clear theoretical understanding of physical processes first of all behind the simplest "basic" multi-pulse sequences which include such a popular sequence as multi-pulse spin locking—MW-4, and a sequence of identically spaced coherent radio frequency (RF) pulses with intervals between them less than the time constant of free induction decay (FID) —strong off-resonance comb— SQRC. ... 

Figure 9a. Timing diagram for SORC sequence (Strong Off-Resonance Comb of rf pulses).

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