Cancellation of extraneous signals in NQR spectroscopy

In an NOR system, extraneous signals such as magneto-acoustic ringing, piezo-electric ringing, electronic circuit ringing and baseline offset are eliminated by applying a pulse sequence to a specimen which generates two sets of oppositely phased NOR echo signals. The NQR echo signals of one phase are subtracted from the echo signals of the opposite phase, producing a cumulative echo signal and simultaneously cancelling out the same-phase extraneous signals. The applied pulse sequence may be a spin-locked inversion mid-echo (SLIME) pulse sequence which only has a single excitation pulse. The system may be used to detect explosives and drugs.