The multi-pulse method of detecting nuclear quadrupole resonance (NQR) in explosives containing polycrystalline RDX has been investigated. The following sequences were used: a spin-locking type sequence (SLS), a phase-alternated pulse sequence (PAPS) and a sequence without a preparatory pulse. The SLS, PAPS and strong off-resonance comb methods with the same parameters are of great interest for practical applications. The influence of the frequency offset on NQR signals in multi-pulse experiments was studied.
A special pulsed instrument has been constructed for short-range remote nuclear quadrupole resonance experiments. The instrument was designed for detection of nitrogen-14 chemical compounds (in the low-frequency band 0.5-10 MHz). High sensitivity has been achieved by using a special construction of main sub-units and optimum experimental techniques. A description of the construction and performance of this instrument is given. As an example the results of the short-range remote detection of RDX are presented.
PACS 76.60.GvTheoretical and practical aspects of using multi-pulse spin-locking and the "strong off-resonant comb" (SORC) sequence for detecting nitrogenated substances by the nuclear quadrupole resonance method were studied. A number of optimum correlations between the parameters of multi-pulse sequences and the relaxation characteristics of the substances under investigation were determined. The obtained relations were used for the fast detection of α-trinitrotoluene (TNT). Relaxation parameters and temperature coefficients for twelve 14 N lines of the orthorhombic phase of TNT measured at room temperature are also presented.
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