| abstract |
This invention involves an apparatus to measure the nuclear quadrupole (NQR) response of a specimen using three frequencies. Three-frequency NQR involves excitation of at least two transitions that causes an observed signal at a third transition frequency. Thus, the transition excited and detected is not irradiated at all. This reduces undesirable interfering signals due to the excitation, for example as a result of acoustic ringing and/or tank circuit ring-down, since the excitation is not applied at the frequency that is detected. This invention will be particularly useful to detect substances selected from the group consisting of explosives and narcotics using nitrogen NQR. |