Pulse sequences for exciting nuclear quadrupole resonance

1. A nuclear quadrupole resonance apparatus for detecting a target substance containing quadrupole nuclei, comprising:

a pulse sequence generator to generate a combination of multi-pulse sequences with pulse intervals longer than the time constant of free induction decay T 2 *, but shorter than the time of spin-spin relaxation T 2 , and to generate a preparatory pulse or group of preparatory pulses for creating echo signals between the pulses of the multi-pulse sequences;

a detector to detect nuclear quadrupole resonance signals generated from the target substance under conditions of unknown temperature of the target substance in response to the combination of multi-pulse sequences; and

a combiner to combine the detected nuclear quadrupole resonance signals generated under conditions of unknown temperature of the target substance into a resulting signal such that the resulting signal contains a prevailing echo component produced by the preparatory pulse or group of preparatory pulses, thereby mitigating the effect of intensity variations.

2. A method of nuclear quadrupole resonance for detecting a target substance containing quadrupole nuclei, the method comprising the steps of:

generating a combination of multi-pulse sequences, at least one of which contains a preparatory pulse or group of preparatory pulses, having intervals between pulses longer than the time constant of free induction decay T 2 *, but shorter than the time of spin-spin relaxation T 2 ;

irradiating the target substance with the combination of multi-pulse sequences;

detecting nuclear quadrupole resonance signals generated from the target substance under conditions of unknown temperature of the target substance in response to the combination of multi-pulse sequences; and

combining the detected nuclear quadrupole resonance signals generated under conditions of unknown temperature of the target substance into a resulting signal where echo generated by the preparatory pulse or group of preparatory pulses is a prevailing components, thereby mitigating the effect of intensity variations.

3. A method as claimed in claim 2 , wherein the combination contains at least one sequence.

4. A method as claimed in claim 2 , wherein the flip angles of pulses of sequences of the combination range between 60° and 345°.

5. A method as claimed in claim 2 , wherein at least one preparatory pulse is composite.

6. A method as claimed in claim 2 , wherein all pulse sequences of the combination contain a preparatory pulse or a group of preparatory pulses.

7. A method as claimed in claim 2 , wherein the carrier frequency of the pulse sequences is near to one of NQR frequencies of the target substance to be detected.

8. A method as claimed in claim 2 , wherein the target substance to be detected comprises an explosive containing quadrupole nuclei.

9. A method as claimed in claim 2 , wherein the target substance to be detected comprises a narcotic containing quadrupole nuclei.

10. An apparatus for producing a multi-pulse sequence for irradiating a target substance containing quadrupole nuclei, comprising:

a generator to generate a combination of multi-pulse sequences with pulse intervals longer than the time constant of free induction decay T 2 *, but shorter than the time of spin-spin relaxation T 2 , and containing a preparatory pulse or group of preparatory pulses for creating echo signals between the pulses of the multi-pulse sequences organised so that the resulting signal contains a prevailing echo component produced by the preparatory pulse or group of preparatory pulses; and

a detector to detect nuclear quadrupole resonance signals generated from the target substance under conditions of unknown temperature of the target substance in response to the combination of multi-pulse sequences.

11. A nuclear quadrupole resonance apparatus for detecting a target substance containing quadrupole nuclei, comprising:

means for generating a combination of multi-pulse sequences with pulse intervals longer than the time constant of free induction decay T 2 *, but shorter than the time of spin-spin relaxation T 2 , and for generating a preparatory pulse or group of preparatory pulses for creating echo signals between the pulses of the multi-pulse sequences;

means for detecting nuclear quadrupole resonance signals generated from the target substance under conditions of unknown temperature of the target substance in response to the combination of multi-pulse sequences; and

means for combining the detected nuclear quadrupole resonance signals into a resulting signal such that the resulting signal contains a prevailing echo component produced by the preparatory pulse or group of preparatory pulses, thereby mitigating the effect of intensity variations.

12. An apparatus for producing a multi-pulse sequence for irradiating a target substance provided with quadrupole nuclei, comprising:

generator means for generating a combination of multi-pulse sequences with pulse intervals longer than the time constant of free induction decay T 2 *, but shorter than the time of spin-spin relaxation T 2 , and containing a preparatory pulse or group of preparatory pulses for creating echo signals between the pulses of the multi-pulse sequences organised so that the resulting signal contains a prevailing echo component produced by the preparatory pulse or group of preparatory pulses; and

detector means for detecting nuclear quadrupole resonance signals generated from the target substance under conditions of unknown temperature of the target substance in response to the combination of multi-pulse sequences.