Removing the effects of acoustic ringing in the detection of explosives by NQR

摘要

The invention relates to a method for detecting a substance selected from the group consisting of explosives and narcotics, in a specimen by nuclear quadrupole resonance. The method comprises the steps of: (a) generating a steady state free precession pulse sequence having a predetermined frequency; (b) transmitting said steady state free precession pulse sequence to a coil; (c) irradiating the specimen in response to said steady state free precession pulse sequence transmitted to said coil at said step (b); (d) detecting a total nuclear quadrupole resonance signal in response to irradiating the specimen at said step (c); (e) receiving said total nuclear quadrupole resonance signal detected at said step (d); (f) repeating step (a) through (e) at a second frequency sufficiently off resonance from the nuclear quadrupolar resonance signal of a nucleus detectable at said first frequency that no nuclear quadrupolar resonance signal for said nucleus occurs at said second frequency; g) subtracting the total nuclear quadrupolar resonance signal obtained in step (f) from the total nuclear quadrupolar resonance signal obtained in step (e).