Abstract: According to the invention, a magnetic field gradiometer detector for detecting a material of interest positioned in a detecting region outside the detector includes a transmitter for generating an output signal at a selected frequency, a receiver for detecting the signal, a probe, and a switch coupling the receiver and transmitter with the probe that alternately connects and disconnects the receiver and transmitter to the probe, switching between transmitting and receiving. The probe includes tuning elements and a gradiometer coil array. The gradiometer coil array includes a first surface coil and a second surface coil wound in an opposite sense, the probe having a first side and an opposite second side, with the first and second surface coils configured asymmetrically such that the probe projects a magnetic field in the outside detecting region adjacent to the first side while being self-shielded on the second side.

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.

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.

Abstract: An apparatus which includes a probe for detecting a resonance signal induced in a sample. The probe and the resonance signal each have a respective, corresponding Q, and the ratio, Q′, of the Q of the probe to the Q of the resonance signal is relatively large. Preferably, Q′ is greater than, or equal to, 1.

Abstract: A noise immune gradiometer split shield coil for use in magnetic resonance etection, such as in Nuclear Magnetic Resonance (NMR) and Nuclear Quadrupole Resonance (NQR). The coil is formed by a transmission line configured as a magnetic field gradiometer. The transmission line has a conductor which is electrically continuous through the coil, and a shield which is split at a position that causes the gradiometer to be electrically balanced. In this manner, the coil provides a high degree of internal shielding to reduce the effects of environmental noise pick-up. Such coils are also less sensitive to the effects of nearby conducting media.