Hybrid stoichiometric analysis and imaging using non-thermal and thermal neutrons

• US 20060227920A1
• Filed: 12/06/2005
• Published: 10/12/2006
• Est. Priority Date: 02/18/1998
• Status: Abandoned Application

• Current Assignee: Bioatom, Calsec California Science & Engineering Corporation, Clear Path Technologies Incorporated, Hiet Acquisition, LLC
• Original Assignee: Calsec California Science & Engineering Corporation
• Inventors: Maglich, Bogdan C.
• Application Number:
  US11/295,746
• Publication Number:
  US 20060227920A1
• Time in Patent Office: Days
• US Class Current: 376/158
• CPC Class Codes: G01N 23/222 using neutron activation analysis [NAA]

Abstract

An apparatus and method for analyzing and imaging chemical compounds within a test subject uses subatomic particle activation. The test subject (and chemical compounds contained therein) is irradiated by non-thermal neutrons, thereby generating thermal neutrons within the test subject and stimulating the emission of gamma rays. Gamma ray detectors detect the emitted gamma rays and energy signals derived from the gamma ray detectors are filtered to eliminate non-relevant spectral artifacts.

Claims

1. A method of providing non-invasive, stoichiometric analysis and imaging of a substance through a barrier, the substance comprising atomic nuclei which emit one or more gamma rays in response to neutron irradiation, the gamma rays having energies characteristic of the atomic nuclei, the method comprising:

emitting a plurality of neutron/alpha particle pairs from a location separate from the substance, each pair comprising a neutron having an energy of approximately 14 MeV and a corresponding alpha particle, the neutron and the alpha particle of each pair propagating in substantially opposite directions;

detecting alpha particles propagating from the location in a direction generally away from the substance;

irradiating a region of the substance with neutrons emitted from the location, the neutrons propagating through the barrier and interacting with atomic nuclei in the region to emit a first plurality of gamma rays from the region through the barrier and to produce a plurality of thermal neutrons in the region, the thermal neutrons interacting with atomic nuclei in the region to emit a second plurality of gamma rays from the region through the barrier;

generating a first plurality of gamma detection signals corresponding to a detected portion of the first plurality of gamma rays detected by a solid-state photon detector having an energy resolution less than or equal to approximately 0.5%;

generating a second plurality of gamma detection signals corresponding to a detected portion of the second plurality of gamma rays detected by the solid-state photon detector;

selecting one or more energies characteristic of at least one of the atomic nuclei of the substance;

energy-filtering the first plurality of gamma detection signals to generate a first plurality of energy-filtered gamma signals by passing gamma detection signals corresponding to detected gamma rays having the selected energies and by rejecting gamma detection signals corresponding to detected gamma rays not having the selected energies;

detecting coincidences between the first plurality of energy-filtered gamma signals and the detected alpha particles; and

energy-filtering the second plurality of gamma detection signals to generate a second plurality of energy-filtered gamma signals by passing gamma detection signals corresponding to detected gamma rays having the selected energies and by rejecting gamma detection signals corresponding to detected gamma rays not having the selected energies.

2. The method of claim 1, further comprising using the detected coincidences to generate an image of the substance.

3. The method of claim 1, wherein energy-filtering the second plurality of gamma detection signals is performed substantially simultaneously with energy-filtering the first plurality of gamma detection signals.

4. The method of claim 1, wherein energy-filtering the second plurality of gamma detection signals is performed before energy-filtering the first plurality of gamma detection signals.

5. The method of claim 1, wherein the substance comprises a nitrogen-containing explosive material and the selected energies comprise energies characteristic of nitrogen nuclei.

6. The method of claim 5, wherein the selected energies further comprise energies characteristic of oxygen nuclei.

7. The method of claim 6, wherein the selected energies further comprise energies characteristic of carbon nuclei.

8. The method of claim 5, wherein the selected energies further comprise energies characteristic of carbon nuclei.

9. The method of claim 1, wherein the substance comprises a chlorine-containing material and the selected energies comprise energies characteristic of chlorine nuclei.

10. The method of claim 1, wherein the substance comprises a hydrogen-containing material and the selected energies comprise energies characteristic of hydrogen nuclei.

11. The method of claim 1, wherein the substance comprises a sulfer-containing material and the selected energies comprise energies characteristic of sulfer nuclei.

12. The method of claim 1, wherein the barrier comprises steel.

13. The method of claim 1, wherein the neutron/alpha particle pairs are generated in a non-pulsed direct-current mode.

14. The method of claim 1, wherein the solid-state photon detector has an energy resolution of approximately 0.3%.

15. The method of claim 1, wherein the solid-state photon detector has an energy resolution on the order of 0.1%.

16. The method of claim 1, wherein the detected gamma rays have energies between 1.6 MeV and 7.2 MeV.

17. The method of claim 1, further comprising using the second plurality of energy-filtered gamma signals to calculate one or more stoichiometric atomic ratios of the atomic nuclei present in the substance.

18. The method of claim 17, wherein the stoichiometric atomic ratios comprise one or more of the nitrogen-to-oxygen stoichiometric atomic ratio, the nitrogen-to-carbon stoichiometric atomic ratio, and the carbon-to-oxygen stoichiometric atomic ratio.

19. The method of claim 17, further comprising identifying the substance from the one or more stoichiometric atomic ratios.

20. The method of claim 17, further comprising determining an empirical chemical formula of the substance from the one or more stoichiometric atomic ratios.

21. The method of claim 1, wherein generating the first plurality of gamma detection signals comprises processing the first plurality of gamma detection signals using a constant fraction discriminator and electronically gating the first plurality of gamma detection signals.

22. The method of claim 1, wherein generating the second plurality of gamma detection signals comprises processing the second plurality of gamma detection signals using a constant fraction discriminator and electronically gating the second plurality of gamma detection signals.

23. A method of providing non-invasive, stoichiometric analysis and imaging of a substance, the substance comprising atomic nuclei which emit one or more gamma rays in response to neutron irradiation, the gamma rays having energies characteristic of the atomic nuclei, the method comprising:

irradiating the substance with 14-MeV neutrons generated in neutron/alpha particle pairs, each pair comprising a 14-MeV neutron and an alpha particle propagating in a substantially opposite direction to the neutron, wherein said irradiation generates thermal neutrons within the substance;

detecting at least a portion of the alpha particles from the neutron/alpha particle pairs, the detected alpha particles propagating in a direction generally away from the substance;

generating a first plurality of gamma detection signals corresponding to a detected portion of a first plurality of gamma rays generated by interactions of the 14-MeV neutrons with atomic nuclei in the substance, the detected portion of the first plurality of gamma rays detected with an energy resolution less than or equal to approximately 0.5%;

generating a second plurality of gamma detection signals corresponding to a detected portion of a second plurality of gamma rays generated by interactions of the thermal neutrons with atomic nuclei in the substance, the detected portion of the second plurality of gamma rays detected with an energy resolution less than or equal to approximately 0.5%;

selecting one or more energies characteristic of at least one of the atomic nuclei of the substance;

energy-filtering the first plurality of gamma detection signals to generate a first plurality of energy-filtered gamma signals by passing gamma detection signals corresponding to detected gamma rays having the selected energies and by rejecting gamma detection signals corresponding to detected gamma rays not having the selected energies;

detecting coincidences between the first plurality of energy-filtered gamma signals and the detected alpha particles; and

energy-filtering the second plurality of gamma detection signals to generate a second plurality of energy-filtered gamma signals by passing gamma detection signals corresponding to detected gamma rays having the selected energies and by rejecting gamma detection signals corresponding to detected gamma rays not having the selected energies.

24. A method of providing non-invasive, stoichiometric analysis and imaging of a substance, the substance comprising atomic nuclei which emit one or more gamma rays in response to neutron irradiation, the gamma rays having energies characteristic of the atomic nuclei, the method comprising:

irradiating the substance with non-thermal neutrons generated in neutron/alpha particle pairs, each pair comprising a non-thermal neutron and an alpha particle propagating in a substantially opposite direction to the neutron, wherein said irradiation generates thermal neutrons within the substance;

detecting at least a portion of the alpha particles from the neutron/alpha particle pairs, the detected alpha particles propagating in a direction generally away from the substance;

generating a first plurality of gamma detection signals corresponding to gamma rays generated by interactions of the non-thermal neutrons with atomic nuclei in the substance, the first plurality of gamma detection signals having an energy resolution less than or equal to approximately 0.5%;

generating a second plurality of gamma detection signals corresponding to gamma rays generated by interactions of the thermal neutrons with atomic nuclei in the substance, the second plurality of gamma detection signals having an energy resolution less than or equal to approximately 0.5%;

energy-filtering the first plurality of gamma detection signals to generate a first plurality of energy-filtered gamma signals by passing gamma detection signals corresponding to energies characteristic of at least one of the atomic nuclei of the substance and by rejecting gamma detection signals corresponding to energies which are not characteristic of at least one of the atomic nuclei of the substance;

detecting coincidences between the first plurality of energy-filtered gamma signals and the detected alpha particles; and

energy-filtering the second plurality of gamma detection signals to generate a second plurality of energy-filtered gamma signals by passing gamma detection signals corresponding to energies characteristic of at least one of the atomic nuclei of the substance and by rejecting gamma detection signals corresponding to energies which are not characteristic of at least one of the atomic nuclei of the substance.

25. A method of providing non-invasive, stoichiometric analysis and imaging of a substance through a barrier, the substance comprising atomic nuclei which emit one or more gamma rays in response to neutron irradiation, the gamma rays having energies characteristic of the atomic nuclei, the method comprising:

emitting a plurality of neutron/alpha particle pairs from a location separate from the substance, each pair comprising a neutron having an energy of approximately 14 MeV and a corresponding alpha particle, the neutron and the alpha particle of each pair propagating in substantially opposite directions;

detecting alpha particles propagating from the location in a direction generally away from the substance;

irradiating a region of the substance with neutrons emitted from the location, the neutrons propagating through the barrier and interacting with atomic nuclei in the region to emit a first plurality of gamma rays from the region through the barrier and to produce a plurality of thermal neutrons in the region, the thermal neutrons interacting with atomic nuclei in the region to emit a second plurality of gamma rays from the region through the barrier;

generating a first plurality of gamma detection signals corresponding to a detected portion of the first plurality of gamma rays;

generating a second plurality of gamma detection signals corresponding to a detected portion of the second plurality of gamma rays;

selecting a set of one or more energies characteristic of at least one of the atomic nuclei of the substance;

energy-filtering the first plurality of gamma detection signals to generate a first plurality of energy-filtered gamma signals by passing gamma detection signals corresponding to detected gamma rays with energies within the set of energies and by rejecting gamma detection signals corresponding to detected gamma rays with energies not within the set of energies;

detecting coincidences between the first plurality of energy-filtered gamma signals and the detected alpha particles; and

energy-filtering the second plurality of gamma detection signals to generate a second plurality of energy-filtered gamma signals by passing gamma detection signals corresponding to detected gamma rays with energies within the set of energies and by rejecting gamma detection signals corresponding to detected gamma rays with energies not within the set of energies.