Baggage inspection apparatus and method for determining presences of explosives

Apparatus for conducting baggage inspection for explosives characterized by having a relatively long T.sub.1 and relatively short T.sub.2, the apparatus comprising:

• (a) a conveyor system for receiving and moving a bag thereon, the bag to be investigated for explosives above a certain quantity therein;
• (b) magnet means for forming lines of flux across the path of said conveyor system to intercept baggage thereon for polarizing hydrogen nuclei in the materials of the bag and its contents;
• (c) coil means for forming a right angle field to the field formed by said magnet at a selected RF frequency for an interval;
• (d) particle resonance detection circuit means connected to said coil means for determining a signal from materials within the baggage;
• (e) circuit means connected to said detection means for detecting signals from hydrogen in materials having a long T.sub.1 and short T.sub.2 ;
• (f) wherein said circuit means includes timing means for forming a first set of interrogation pulses for said coil means;
• (g) storage means for receiving and storing a first image from said detection means;
• (h) storage means for receiving and storing a second image from said detection means;
• and
• (i) means for subtracting the first image from the second image to obtain a null indicative that no explosive material is present wherein the explosive is characterized by a long T.sub.1 and a short T.sub.2.

Apparatus for conducting baggage inspection for explosives characterized by having a relatively long T.sub.1 and relatively short T.sub.2, the apparatus comprising:

• (a) a conveyor system for receiving and moving a bag thereon, the bag to be investigated for explosives above a certain quantity therein;
• (b) magnet means for forming lines of flux across the path of said conveyor system to intercept baggage thereon for polarizing hydrogen nuclei in the materials of the bag and its contents;
• (c) coil means for forming a right angle field to the field formed by said magnet at a selected RF frequency for an interval;
• (d) particle resonance detection circuit means connected to said coil means for determining a signal from materials within the baggage;
• (e) circuit means connected to said detection means for detecting signals from hydrogen in materials having a long T.sub.1 and short T.sub.2 ;
• (f) wherein said magnet means is comprised of first and second separate magnets spaced serially along said conveyor system;
• (g) magnetic field intensity sensor means deployed within the field formed by said first magnet from measuring the intensity of the field impinging on the baggage and its contents;
• (h) magnetic field regulator means connected to said field sensor means;
• and
• (i) magnet power supply means operated by said magnetic field regulator means for forming a variable current applied to said second magnet for altering the magnetic field intensity formed by said second magnet to obtain a specified field intensity in the second field dependent in part on the measurement of said field intensity sensor means.

A method of detecting explosives in baggage and the contents thereof comprising the steps of:

• (a) passing the baggage through a first magnetic field to obtain polarization of hydrogen nuclei;
• (b) placing the baggage in a second magnetic field after polarization;
• (c) transmitting RF pulse energy into the baggage in the second field to initiate an NMR response;
• (d) receiving the NMR response;
• (e) storing the received NMR response to comprise a first image;
• (f) repeating the step of transmitting RF pulse energy into the baggage to obtain a second NMR response;
• wherein the second NMR response is obtained so rapidly after the first NMR response that materials having a long T.sub.1 do not have sufficient time to polarize;
• (g) storing the second NMR response to comprise a second image;
• (h) subtracting one of the images from the other to obtain a difference between the two images;
• and
• (i) evaluating the obtained difference for a null indicative of no explosives in the baggage.

A method of distinguishing hydrogen in compounds in baggage to detect explosive compounds of hydrogen characterized by a long T.sub.1 and short T.sub.2 and to distinguish other compounds of hydrogen having a long T.sub.1 and long T.sub.2 comprising the steps of:

• (a) polarizing hydrogen nuclei in a magnetic field;
• (b) transmitting a sequence of RF pulses into the baggage at right angles to the polarizing field to form first and subsequent NMR echos from the baggage;
• and
• (c) observing the subsequent NMR echos to distinguish long T.sub.1, long T.sub.2 hydrogen materials by a larger subsequent echo compared to the echo from a long T.sub.1, short T.sub.2 material.

Apparatus for conducting baggage inspection for explosives characterized by having a relatively long T.sub.1 and relatively short T.sub.2, the apparatus comprising:

• (a) a conveyor system for receiving and moving a bag thereon, the bag to be investigated for explosives above a certain quantity therein;
• (b) magnet means for forming lines of flux across the path of said conveyor system to intercept baggage thereon for polarizing hydrogen nuclei in the materials of the bag and its contents;
• (c) coil means for forming a right angle field to the field formed by said magnet at a selected RF frequency for an interval;
• (d) particle resonance detection circuit means connected to said coil means for determining a signal from materials within the baggage;
• (e) circuit means connected to said detection means for detecting signals from hydrogen in materials having a long T.sub.1 and short T.sub.2 ;
• (f) means for digitizing signals from said circuit means;
• (g) digital storage means for storing digital data from said digitizing means;
• (h) timing means operating an RF pulse forming means to form first and second identical RF pulse trains supplied to said coil means;
• and
• (i) means for subtracting the digitized responses to the first and second RF pulse trains to obtain a null indicative of no long T.sub.1 materials in the baggage.