USA As Represented by Secretary of the Navy

Other

Michael L Buess

Joel B Miller

Allen N Garroway

James P Yesinowski

Roy P Lindquist

Allen M Garroway

A method and apparatus for screening samples to determine which samples include a target material. Generally, the samples are pre-screened to determine which of the samples have a piezoelectric resonance when irradiated with an electric field, to thereby indicate the presence of the target material. The samples that have the piezoelectric resonance are then further screened by a different process to confirm the presence of the target material. For example, samples that have the piezoelectric resonance are further screened for a specific nuclear quadrupole resonance (NQR), a specific nuclear magnetic resonance (NMR) or a specific visual characteristic, to confirm the presence of the target material in the sample. The apparatus and method can be used, for example, to search luggage at ports of entry for the presence of cocaine hydrochloride or heroin hydrochloride.

Method and apparatus for detecting a target material in a sample by pre-screening the sample for piezoelectric resonance

A Nuclear Quadrupole Resonance (NQR) method and apparatus for detecting the presence of a nitramine explosive, with a reduced probability of spurious triggering of consumer electronics. In the method and apparatus, a signal is emitted towards a nitramine explosive so that a nitro group in the namine explosive produces an NQR resonance signal. The NQR resonance signal is then detected to thereby detect the presence of the nitramine explosive. If the nitramine explosive is RDX, the NQR resonance signal of the nitro group is at a frequency which is either 502.3 kHz, 500.5 kHz, 405.1 kHz, 396.2 kHz or 384.1 kHz. Such frequencies are much lower than those in conventional detection techniques. As a result, the probability of the undesirable spurious triggering of electronic items exposed to the NQR RF pulses will be reduced, due to the reduction in induced voltage at lower frequency. The detection sensitivity is also reduced, but in many cases will still be adequate to detect nitramine explosives.

Nuclear quadrupole resonance (NQR) method and apparatus for detecting a

Acoustic ringing and adverse effects from variations in the NQR detection of explosives and narcotics are minimized or eliminated. A specimen is irradiated with a modified steady state steady state free precession (SSFP) pulse sequence which combines a phase-alternated pulse sequence (PAPS) with a non-phase-alternated pulse sequence (NPAPS). The resulting signals from the PAPS and NPAS may then be coadded to cancel out the FID contributions to the signals. By canceling out the FID contributions to the signals, the effects of probe ringing and other extraneous responses, as well as the effect of temperature variation, are minimized or removed. The present method is especially effective in the detection of explosives and narcotics having .sup.14 N or .sup.35,37 Cl nuclei. A steady state free precession pulse which is especially useful with the method of the present invention is the strong off-resonance comb (SORC). In another embodiment of the invention, the effects of probe ringing can also be minimized or removed by repeating the detection procedure at a frequency which is sufficiently off-resonance so that only frequency independent effects, such as probe-ringing, can be observed.

Removing the effects of acoustic ringing and reducing temperature

The sensitive detection of explosives and narcotics by nuclear quadrupole resonance (NQR) is performed at low rf power by assuring that the rf field strength is larger than the local magnetic field. Additionally, it has been recognized that signal-to-noise ratio of a signal induced by a specimen of fixed size decreases by only the square root of the coil size. Thus, rather than scaling power linearly with coil size, as conventionally done to maintain the same rf field intensity, the power need only be increased by the square root of the increased coil size to assure maintenance of the same signal to noise ratio. This technique permits the use of larger coils than previously used. The invention is useful for both volume coils and surface coils.

Detection of explosive and narcotics by low power large sample volume

A system and method for detecting a class of explosives and narcotics containing nitrogen in a specimen by nuclear quadrupole resonance which improves the selectivity, sensitivity and spatial localization over conventional detection systems. As a result, sub-kilogram quantities of explosives and narcotics against a background of more benign materials may be detected by the nuclear quadrupole resonance system and method. Also, by the use of a meanderline surface coil, the electrical and magnetic fields will fall off rapidly over a short distance so that a localized region may be scanned and people may be scanned without depositing substantial RF power into the body. Furthermore, by using a strong off-resonance comb (SORC) irradiation sequence, the signal-to-noise ratio of the detected signal is improved for obtaining a more accurate detection signal from the specimen.

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Alexandria, VA, United States of America

Michael L Buess