Improved 14N nuclear quadrupole resonance detection of trinitrotoluene using polarization transfer from protons to 14N nuclei

Combination of proton-nitrogen level crossing polarization transfer and pulsed spin-locking sequence makes N-14 nuclear quadrupole resonance (NQR) in trinitrotoluene fast and sensitive enough to be used in routine detection of explosives. Enhancement factors for all three N-14 NQR lines (the case with eta not equal 0) were calculated and compared with experimental values. Good agreement between measured and calculated signal enhancement factors was observed. N-14 NQR signals in a 15 g trinitrotoluene sample of predominantly monoclinic modification were measured in 15 s in different polarization magnetic fields. The conditions for optimal proton-nitrogen level crossing were determined. (C) 2007 American Institute of Physics.