Density detection using discrete photon counting

• US 20010020682A1
• Filed: 04/12/2001
• Published: 09/13/2001
• Est. Priority Date: 10/23/1995
• Status: Active Grant

• Current Assignee: Science Applications International Corporation
• Original Assignee: Science Applications International Corporation
• Inventors: Orphan, Victor J., Smith, Scott T., Verbinski, Victor V., Valentine, Kenneth H.
• Granted Patent: US 6,552,346 B2
• Time in Patent Office: Days
• US Class Current: 250/358.1
• CPC Class Codes: G01N 23/02 by transmitting the radiation through the material
• CPC Class Codes: G01V 5/22 Active interrogation, i.e. by irradiating objects or goods using external radiation sources, e.g. using gamma rays or cosmic rays

Abstract

A system and method of density detection in a target object involve irradiating the target object, detecting a first and second discrete number of photons penetrating the target object through respective first and second prescribed volumes and entering respective first and second radiation detectors. First and second numbers of photons detected by the first and second radiation detectors are counted, and a display output signal is generated in response to the first and second numbers. A graphical representation of the densities within the first and second volumes of the target object is displayed.

Claims

1. A system for measuring relative densities of materials contained within a target object comprising:

a radiation source for directing radiation toward the target object;

a detector array coupled to the radiation source for receiving radiation passing through the target object; and

a discriminator coupled to the detector array for generating a pulse only in response to a waveform corresponding to a received photon that exceeds a selected noise threshold; and

a counter coupled to the discriminator.

2. The system of

claim 1

further comprising a display device coupled to the counter for displaying relative densities of materials contained within the target object.

3. The system of

claim 2

wherein the graphical display includes means for retrieving a stored display and means for concurrently displaying the stored display and the relative densities of materials contained within the target object.

4. The system of

claim 1

wherein the radiation source is a gamma radiation source.

5. The system of

claim 4

further comprising a shutter coupled to the gamma radiation source.

6. The system of

claim 4

wherein the radiation source generates gamma radiation having an energy of about 662 keV.

7. The system of

claim 1

wherein the radiation source has an intensity of about 3.7×

10¹⁰ Bq .

8. The system of

claim 1

further comprising a motion controller for maintaining a substantially constant distance between the radiation source and the detector array.

9. The system of

claim 1

further comprising:

a radiation source platform coupled to the radiation source including a first drive motor; and

a detector array platform coupled to the detector array including a second drive motor generally synchronized with the first drive motor.

10. The system of

claim 1

wherein the target object is selected from the group consisting of a vehicle, a cargo container, and a railroad car.

11. A method of measuring relative densities of materials contained within a target object comprising the steps of:

(a) directing radiation from a radiation source toward the target object;

(b) detecting radiation passing through the target object to generate a corresponding waveform for each photon detected;

(c) discriminating the corresponding waveform to generate a pulse only if the corresponding waveform exceeds a selected noise threshold of a discriminator; and

(d) counting the pulse with a counter.

12. The method of

claim 11

further comprising the step of (e) displaying a pulse count representative of relative densities of materials contained within the target object.

13. The method of

claim 11

wherein the target object is selected from the group consisting of a vehicle, a cargo container, and a railroad car.

14. The method of

claim 11

wherein step (b) includes moving the radiation source and the detector array relative to the target object during a time when the target object is stationary.

15. The method of

claim 11

wherein step (a) includes directing gamma photons from the radiation source.

16. The method of

claim 15

wherein the gamma photons have an energy of 662 keV.

17. The method of

claim 15

wherein the radiation source is controlled by a shutter.

18. A system for measuring relative densities of materials contained within a target object comprising:

a radiation source for radiating photons toward the target object;

an array of photon detectors coupled to the radiation source for receiving photons passing through the target object;

moving means for moving at least one of the radiation source, the array of photon detectors, and the target vehicle so as to maintain a constant distance between the radiation source and the array of photon detectors;

a discriminator coupled to the array of photon detectors for generating a pulse only in response to a waveform corresponding to a received photon that exceeds a selected noise threshold; and

a counter coupled to the discriminator.

19. The system of

claim 18

further comprising a display device coupled to the counter for displaying relative densities of materials contained within the target object.

20. The system of

claim 18

wherein the display device comprises mapping means for mapping a counted number of pulses for each photon detector to a color.

21. The system of

claim 18

wherein the display device comprises mapping means for mapping a counted number of pulses for each photon detector to a gray-scale.

22. A method of measuring relative densities within a target object comprising the steps of:

irradiating the target object, the target object being selected from the group consisting of a vehicle, a cargo container, and a railroad car;

detecting a first discrete number of photons penetrating the target object through a first prescribed volume and entering a first radiation detector;

detecting a second discrete number of photons penetrating the target object through a second prescribed volume and entering a second radiation detector;

discriminating an amplified output of the first radiation detector with a discriminator to generate a first number of pulses only in response to waveforms in the amplified output of the first radiation detector that exceed a selected noise threshold;

counting the first number of pulses with a counter;

discriminating an amplified output of the second radiation detector with a discriminator to generate a second number of pulses only in response to waveforms in the amplified output of the second radiation detector that exceed a selected noise threshold;

counting the second number of pulses with a counter; and

displaying a graphical representation of relative densities within the first volume of the target object in response to the first number of pulses and within the second volume of the target object in response to the second number of pulses.

23. The method of

claim 22

wherein the step of displaying includes:

mapping the first number of pulses to a first color; and

mapping the second number of pulses to a second color.

24. The method of

claim 22

wherein the step of displaying includes mapping the first number of pulses to a first shade of gray and mapping the second number of pulses to a second shade of gray.

25. A system for measuring relative densities within a target object comprising:

a source platform;

a detector platform;

a radiation source positioned on the source platform;

a detector array positioned on the detector platform wherein the detector array comprises a plurality of photon detectors;

a motor coupled to at least one of the source platform and the detector platform for moving the at least one of the source platform and the detector platform so as to maintain a constant distance therebetween to scan at least a portion of the target object;

a discriminator coupled to the detector array for generating a pulse only in response to a waveform corresponding to a received photon that exceeds a selected noise threshold; and

a counter coupled to the discriminator.

26. The system of

claim 25

further comprising a display device coupled to the counter for displaying relative densities of materials contained within the target object.

27. The system of

claim 25

further comprising:

a first track on which the radiation source travels along a first trajectory, and

a second track on which the linear detector array travels along a second trajectory wherein the first trajectory and the second trajectory are substantially parallel.

28. The system of

claim 25

wherein the radiation source generates gamma radiation having an energy of about 662 keV.

29. The system of

claim 25

wherein the radiation source generates radiation at an intensity of about 3.7×

10¹⁰ Bq.

30. A system for measuring relative densities of materials contained within a target object comprising:

a radiation source for directing radiation toward the target object;

a detector array coupled to the radiation source for receiving radiation passing through the target object; and

a discriminator coupled to the detector array for generating a pulse only in response to each waveform corresponding to a received photon that exceeds a selected noise threshold.

31. The system of

claim 30

further comprising a display device coupled to the discriminator for displaying relative densities of materials contained within the target object.

32. The system of

claim 31

wherein the graphical display includes means for retrieving a stored display and means for concurrently displaying the stored display and the relative densities of materials contained within the target object.

33. The system of

claim 30

wherein the radiation source is a gamma radiation source.

34. The system of

claim 30

further comprising a shutter coupled to the gamma radiation source.

35. The system of

claim 30

wherein the radiation source generates gamma radiation having an energy of about 662 keV.

36. The system of

claim 30

wherein the radiation source has an intensity of about 3.7×

10¹⁰ Bq.

37. The system of

claim 30

further comprising a motion controller for maintaining a substantially constant distance between the radiation source and the detector array.