We have analyzed the possibilities of dynamically polarizing proton spin system via the quadrupole 14N spin system. The increase of the proton magnetization was calculated. The proton polarization rate was found to be related to the transition probabilities between the 14N NQR and 1H NMR energy levels. The experiments performed in 1,3,5-triazine confirmed the results of the theoretical analysis. We proposed a new double resonance technique for the measurement of NQR frequencies of the order of 100 kHz and lower.
The off-resonance dependence of the amplitudes of the six dominant 14N nuclear quadrupole resonance (NQR) lines in commercial polymorphic trinitrotoluene (TNT) sample were experimentally and theoretically determined for a wide range of experimental parameters when irradiated with the spin-lock spin-echo (SLSE) pulse sequence. The amplitudes off-resonance dependence follow a sinc-like function with an additional modulation due to the spacing between the RF pulses. The results can be immediately used for improvement of robust signal processing models for the TNT NQR detectors.