Background of the Invention.
Patent Application, Filed 30 Nov 92,
DEPARTMENT OF THE NAVY WASHINGTON DC
Pagination or Media Count:
Acoustic ringing and adverse effects from variations in the NQR detection of explosives and narcotics are minimized or eliminated. A specimen is irradiated with a modified steady state steady state free precession SSFP pulse sequence which combines a phase-alternated pulse sequence PAPS with a non-phase-alternated pulse sequence NPAPS. The resulting signals from the PAS and NPAS may then be coadded to cancel out the FID contributions to the signals. By canceling out the FID contributions to the signals, the effects of probe ringing and other extraneous responses, as well as the effect of temperature variation, are minimized or removed. The present method is especially effective in the detection of explosives and narcotics having 14N or 35,37Cl nuclei. A steady state free precession pulse which is especially useful with the method of the present invention is the strong off-resonance comb SORC. In another embodiment of the invention, the effects of probe ringing can also be minimized or removed by repeating the detection procedure at a frequency which is sufficiently off-resonance so that only frequently independent effects, such as probe-ringing, can be observed
- Acoustic Detection and Detectors