USA As Represented by Secretary of the Navy

Other

Princeton University

Karen L Sauer

Joel B Miller

Allen N Garroway

Christopher A Klug

Young Woo Lee

Michael Romalis

Bryan H Suits

Shouqin Huo

Seung-Kyun Lee

Michael L Bucss

Igor M Savukov

Scott J Seltzer

A device for detecting a class of target species containing quadrupolar nuclei in a specimen by nuclear quadrupole resonance, comprising a pulse generator for generating a three-pulse-composite-pulse to refocus signals that were excited by another pulse, an irradiator for irradiating a specimen with the three-pulse-composite-pulse, a detector for detecting an NQR signal in response to irradiating the specimen, a coupler for transmitting the three-pulse-composite-pulse to the irradiating means, and a transformer for converting the free induction decay signal into a frequency domain signal. A method for detecting a class of target species containing quadrupolar nuclei in a specimen by nuclear quadrupole resonance, comprising generating a three-pulse-composite-pulse, irradiating said specimen with said three-pulse-composite-pulse, detecting an NQR signal in response to irradiating said specimen and converting said free induction decay signal into a frequency domain signal.

Cancellation of ringing artifacts and far field interference in nuclear quadrupole resonance

A radio-frequency tunable atomic magnetometer for detection of nuclear quadrupole resonance (NQR) from room temperature solids, including detection of nitrogen-containing explosives placed external to a sensor unit. A potassium radio-frequency magnetometer with sensitivity of 0.24 fT/Hzoperating at 423 kHz is provided. The magnetometer detected aN NQR signal from room temperature ammonium nitrate (NHNO) in the zero-applied field limit. Results demonstrate first time detection of NQR with an atomic magnetometer, providing that a cryogen-free atomic magnetometer, with intrinsically frequency-independent sensitivity and easy tuning capabilities, can be an attractive new tool for detecting magnetic resonance signals in the kHz to MHz range. Low intensity magnetic fields are measured using an alkali metal vapor, by increasing magnetic polarization of the vapor to increase its sensitivity, then probing the magnetic polarization of the vapor to receive an output, and determining characteristics of the low intensity magnetic field from the output.

Subfemtotesla radio-frequency atomic magnetometer for nuclear quadrupole resonance detection

A magnetic resonance detection apparatus is provided that is not susceptible to acoustic ringing, and a method is provided for eliminating or canceling acoustic ringing from a detected magnetic resonance signal. Specifically, a composite pulse is utilized that allows for both efficient reduction of acoustic ringing signals and the detection of true NQR signals. The composite pulse can be used in any of the common NQR pulse sequences currently utilized simply via substitution of the original single pulses with the composite pulse. Furthermore, although a preferred application involves the spin-1 nucleusN and NQR, the composite pulse will be useful for the NQR of other nuclei such asCI andK and in NMR applications and involving half-integer quadrupolar nuclei and spin- 1/2 nuclei. In addition, coil ringdown and piezoelectric ringing are also substantially reduced.

Cancellation of ringing in magnetic resonance utilizing a composite pulse

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.

Substance detection by nuclear quardrupole resonance using at least two different excitation frequencies

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Fairfax Station, VA, United States of America

Karen L Sauer