Method and system for high energy, low radiation power X-ray imaging of the contents of a target

• US 7,453,987 B1
• Filed: 12/06/2006
• Issued: 11/18/2008
• Est. Priority Date: 03/04/2004
• Status: Active Grant

• Current Assignee: Leidos, Inc. (Leidos Holdings, Inc.)
• Original Assignee: Science Applications International Corporation
• Inventors: Richardson, Rex D
• Primary Examiner(s): KAO, CHIH CHENG G
• Application Number:
  US11/634,218
• Time in Patent Office: 713 Days
• Field of Search: 378/57, 378/98.9
• US Class Current: 378/98.9
• CPC Class Codes: G01V 5/224 Multiple energy techniques using one type of radiation, e.g. X-rays of different energies
• CPC Class Codes: G01V 5/234 Measuring induced radiation, e.g. thermal neutron activation analysis
• CPC Class Codes: G01V 5/281 detecting special nuclear material [SNM], e.g. Uranium-235, Uranium-233 or Plutonium-239

Abstract

The systems and methods described herein automatically detect, highlight and identify high-Z materials in volume concentrations of approximately 100 cm³ or greater utilizing single and/or dual energy sources with x-ray and neutron detectors. The methods and systems described herein are applied to the imaging of containerized cargo and cargo vehicles. Pursuant to the described systems and methods, radiation powers are orders of magnitude lower than those used in the conventional systems. By reducing the radiation power by a factor of, for example, 100 or more, the shielding requirements for the system are greatly reduced, alignment requirements can be significantly relaxed and system components can be lighter weight and more modular. Consequently, system costs are reduced.

Claims

1. A system for imaging a target object comprising:

a source assembly for directing a radiation source at the target object;

a detector component for detecting a level of radiation passing through the target object;

the detector component comprising a plurality of converters that convert the radiation into a signal, the detector component comprising;

a first detector for detecting radiation in an analog mode; and

a second detector for detecting radiation in a discrete photon counting mode; and

a processor for imaging the target object in response to the signal from the detector component;

wherein the processor differentiates between an atomic number by weight of a first material from an atomic number by weight of a second material in the target object;

wherein the converters comprise Cherenkov x-ray converters.

2. The system of claim 1, wherein the system is selected from the group consisting of relocatable, stationary, pallet, mobile having a boom configuration, and mobile having a gantry configuration.

3. The system of claim 2, wherein the mobile system with gantry configuration comprises a plurality of detectors selected from the group consisting of neutron detectors, Cherenkov detectors, and a combination thereof, wherein the plurality of detectors are located on at least two sides of a three-sided carriage.

4. The system of claim 1, wherein the target object is stationary during imaging.

5. The system of claim 1, wherein the source assembly and the detector component are stationary during imaging of the target object.

6. The system of claim 1, further comprising a first track for guiding the source assembly and a second track for guiding the detector component.

7. The system of claim 1, wherein the detector component comprises a plurality of detector panels and each detector panel comprises a plurality of a first detector or a second detector.

8. The system of claim 7, wherein the detector panels are angled.

9. The system of claim 1, wherein the converters comprise non-scintillating materials.

10. The system of claim 1, wherein a time for directing the radiation source at the target object to detect the level of radiation passing through the target object is less than 60 seconds.

11. The system of claim 1, wherein a rate for directing the radiation source at the target object to detect the level of radiation passing through the target object is approximately 8 to 12 inches per second.

12. The system of claim 1, wherein the source assembly comprises a betatron source or a linear accelerator.

13. The system of claim 12, wherein the betatron source emits at approximately 5.0 to 7.5 MeV.

14. The system of claim 12, wherein the linear accelerator operates in an interlaced mode at approximately 5 to 6 MeV and approximately 8 to 10 MeV end point energies.

15. The system of claim 14, wherein the target object receives at most 20 μ

Sv/hour x-ray exposure or neutron exposure at one meter from one of the plurality of converters.

16. The system of claim 12, further comprising an x-ray collimator.

17. The system of claim 16, wherein the x-ray collimator has a beam fan angle of approximately 26 degrees.

18. The system of claim 16, wherein the x-ray collimator comprises a variable slit width.

19. The system of claim 12, wherein the linear accelerator has an approximately 400 Hz total repetition rate.

20. The system of claim 12, wherein the linear accelerator has a combination of at least one low energy pulse and at least one high energy pulse.

21. The system of claim 1, wherein for a target object less than a predetermined thickness, radiation pulses emitted from the radiated target object are converted to analog photomultiplier tube currents;

and for a target object greater than a predetermined thickness, the system performs discrete photon counting.

22. The system of claim 21, wherein the predetermined thickness is 3 inches.

23. The system of claim 1, wherein the processor identifies an atomic number of at least 92.

24. The system of claim 1, wherein the source assembly further comprises a laser alignment system to assist in alignment of the target object with the source assembly.

25. The system of claim 1, further comprising an ion chamber in the path of the radiation to provide substantially real time signals that indicate integrated radiation output for each x-ray pulse.

26. The system of claim 25, wherein each x-ray pulse is approximately 2 to 5 μ

s in duration.

27. The system of claim 25, wherein the substantially real time signals correct image pixel columns for pulse-to-pulse variations.

28. The system of claim 1, wherein each Cherenkov x-ray converter comprises:

a non-scintillating plastic or glass rod; and

a photomultiplier tube.

29. The system of claim 28, wherein the photomultiplier tube has a rise time of approximately 700 picoseconds.

30. The system of claim 28, wherein the interaction of x-rays with the Cherenkov x-ray converter produces Cherenkov radiation including visible light pulses.

31. The system of claim 30, wherein the Cherenkov radiation emits along a Compton recoil electron or positron-electron pair tracks.

32. The system of claim 30, wherein the visible light pulses are less than approximately 300 picoseconds in duration.

33. The system of claim 30, wherein the photomultiplier tube coverts the visible light pulses into current pulses.

34. The system of claim 33, wherein the system uses current pulses for photon counting at a count rate of up to approximately 1 GHz.

35. The system of claim 33, further comprising a processing circuit for discriminating and counting current pulses.

36. The system of claim 35, wherein the processing circuit comprises a comparator, a discriminator, a ripple counter, a microcontroller, a counter, and a microprocessor.

37. The system of claim 36, wherein the comparator has bandwidth of approximately 2.5 GHz and output switching risetime of approximately 150 picoseconds.

38. The system of claim 36, wherein the discriminator excludes visible light pulses.

39. The system of claim 1, wherein the source assembly is configured to operate alternately in a dual energy mode.

40. The system of claim 39, wherein the source assembly provides photon energy at approximately 5 to 150 keV.

41. The system of claim 39, wherein the source assembly provides photon energy at about 1 MeV or greater.

42. The system of claim 39, wherein the source assembly switches the beam energy between at least two values.

43. The system of claim 39, wherein the source assembly provides interlaced outputs of approximately 4 to 6 MeV and approximately 8 to 10 MeV.

44. The system of claim 39, wherein the source assembly has an alternating mode comprised of a 200 Hz low energy pulse train interlaced with a 200 Hz high energy pulse train.

45. The system of claim 1, further comprising a first palette for displaying an image of the target object and a second palette for displaying areas of the target object having an atomic number by weight above a predetermined amount.

46. A method for imaging a target object comprising:

directing radiation from a first radiation source to the target object;

detecting radiation from the irradiated target object at a first detector in analog mode;

directing radiation at the target object after the first detector detects radiation from the irradiated target object;

detecting radiation from the irradiated target object at a second detector in discrete photon counting mode; and

depicting an image of the target object based upon the detected radiation by the first or second detector;

wherein the first detector or second detector comprises a Cherenkov x-ray converter.

47. The method of claim 46, wherein the first and second detectors are a first channel and a second channel, respectively, on a single detector.

48. The method of claim 47, wherein the second detector comprises a plurality of discriminator channels.

49. The method of claim 46, wherein the first radiation source operates in a dual energy mode.

50. The method of claim 49, wherein the first radiation source operates at approximately 4 MeV to 6 MeV in a first mode and approximately 8 to 10 MeV in a second mode.

51. The method of claim 46, wherein a second radiation source directs radiation at the target object after the first detector detects radiation from the irradiated target object.

52. The method of claim 51, wherein the target object is stationary when the second radiation source is directing radiation at the target object.

53. The method of claim 46, wherein the second detector is stationary for the second scan.

54. The method of claim 46, wherein the first radiation source operates at approximately 4 MeV to 6 MeV in a first mode and approximately 8 to 10 MeV in a second mode.