US 5,233,300 A · Detection of explosive and narcotics by low power large sample volume nuclear quadrupole resonance (NQR)

Abstract

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.

Claims16

Dependent claims

A method for detecting a class of explosives and narcotics containing nitrogen in a specimen by nuclear quadrupole resonance, comprising the steps of:

(a) generating a train of radio frequency pulses having a predetermined frequency;
(b) transmitting said train of radio frequency pulses to a coil;
(c) irradiating the specimen with an rf field of predetermined strength in response to said train of radio frequency pulses transmitted to said coil at said step (b), said specimen having a local magnetic field due to dipole-dipole contributions;
(d) detecting an integrated nitrogen signal in response to irradiating the specimen at said step (c);
(e) receiving said integrated nitrogen signal detected at said step (d);
(f) comparing said integrated nitrogen signal to a predetermined threshold value;
and
(g) signalling when said integrated nitrogen signal exceeds said predetermined threshold value;
wherein the ratio of the strength of said predetermined rf field to the strength of said local magnetic field is from about 1:1 to about 50:1.

6 more elements

A system for detecting a class of explosives and narcotics containing nitrogen in a specimen having a local magnetic field due to dipole-dipole contributions, by nuclear quadrupole resonance, said system including:

a coil of predetermined size for irradiating the specimen with a train of radio frequency pulses of predetermined frequency and detecting an integrated nitrogen signal in response to irradiating the specimen;
pulse generating means for generating said train of radio frequency pulses;
coupling means for transmitting said train of radio frequency pulses to said coil and receiving said integrated nitrogen signal from said coil;
comparing means for comparing said integrated nitrogen signal to a predetermined threshold value;
and
an alarm for signalling when said integrated nitrogen signal exceeds said predetermined threshold value;
wherein said pulse-generating means causes said coil to irradiate said specimen with an rf field having a strength which is from about equal to the strength of the local magnetic field of said sample up to about 50 times the strength of the local magnetic field of the specimen.

4 more elements

Dependencies are inferred from the claim text.

Detection of explosive and narcotics by low power large sample volume nuclear quadrupole resonance (NQR)

Life of this patent

Detection of explosive and narcotics by low power large sample volume nuclear quadrupole resonance (NQR)

Life of this patent

Abstract

Claims16