Removing the Effects of Acoustic Ringing and Reducing Temperature Effects in the Detection of Explosives by NQR

摘要

It is an object of the present invention to minimize or eliminate acoustic ringing and adverse effects due to changes in NQR detection of explosive materials and anesthetics. Samples are irradiated with a modified steady state free session (SSEP) pulse sequence that combines a phase-shift pulse sequence (PAPS) and a non-phase-shift pulse sequence (NPAPS). Co-add signals generated from PAPS and NPPAS to cancel FID contributions to the signals. By canceling the FID contributions to the signals, the effect of shape and temperature changes on probe ringing and other external response is minimized or eliminated. The method of the invention is particularly effective in the detection of explosive substances and anesthetics with ¹⁴ N or ^35,37 C1 nuclei. Particularly useful steady state free session pulses in the method of the invention are strong off-resonant combs (SORC).;In another embodiment of the present invention, probe ringing phenomena may also be minimized or eliminated by repeating the detection procedure at a frequency that is sufficiently off-resonant to be able to observe only frequency-independent phenomena such as probe-ringing and the like.