Integrated optical neutron detector

• US 20080237485A1
• Filed: 02/15/2008
• Published: 10/02/2008
• Est. Priority Date: 03/30/2007
• Status: Active Grant

• Current Assignee: 3-D Image Technology
• Original Assignee: Tamper Proof Container Licensing Corp.
• Inventors: Beinhocker, Gilbert D.
• Granted Patent: US 7,619,226 B2
• Time in Patent Office: Days
• US Class Current: 250/474.1
• CPC Class Codes: G01T 1/167 Measuring radioactive content of objects, e.g. contamination whole body counters G01T1/163
• CPC Class Codes: G01T 3/00 Measuring neutron radiation G01T5/00 takes precedence
• CPC Class Codes: G01V 5/26 Passive interrogation, i.e. by measuring radiation emitted by objects or goods
• CPC Class Codes: G01V 5/281 detecting special nuclear material [SNM], e.g. Uranium-235, Uranium-233 or Plutonium-239

Abstract

A system and method for detecting radiation from a source in a container is disclosed. A continuous optical fiber path is disposed in a medium which is part of or associated with a container and which totally encapsulates the inside volumetric space of the container. The optical fiber path provides a volumetric mass of optical fiber which is reactive to radiation from a radiation source in the container to cause an irreversible change in the light carrying capacity or other characteristic of the optical fiber. A light source is coupled to one end of the optical fiber path for introducing light having a predetermined characteristic. A light detector is coupled to the other end of the optical path for receiving light from the optical path. A circuit is coupled to the light detector and is operative to detect a change in the predetermined characteristic of the light and to provide an indication thereof in a fail-safe manner. The extraction of a radiation signal from background radiation noise is achieved using geometric methodologies. The detection system is operative to facilitate the detection of low level flux of thermalized neutrons.

Claims

1. A radiation detection system comprising:

a panel structure sized to line the interior walls of a multi-sided container;

the panel structure having an annealing-resistant optical fiber therein and extending in an optical fiber path across substantially the entire area of the panel structure to envelop substantially the entire volume of the container;

the annealing-resistant optical fiber having a first end and a second end;

the annealing-resistant optical fiber being reactive to nuclear radiation impinging on the optical fiber to cause a change in light carrying capacity of the optical fiber;

a light source optically coupled to one end of the optical fiber for introducing light;

a light detector optically coupled to the other end of the optical fiber for receiving light from the optical fiber; and

a circuit connected to the light detector and operative to detect the change in light carrying capacity of the optical fiber and to provide an indication thereof.

2. The radiation detection system of claim 1 wherein:

the light source is operative to introduce light in the optical fiber path of predetermined intensity and frequency; and

the circuit connected to the light detector is operative to detect at least one of a decrease in intensity of the light from the optical fiber path and a change in the frequency of the light from the optical fiber path, and to provide an indication thereof.

3. The radiation detection system of claim 1 wherein the light source is a tunable laser light source.

4. The radiation detection system of claim 2 wherein the circuit connected to the light detector is operative to determine the rate of decrease in the intensity of light from the optical fiber path.

5. The radiation detection system of claim 1 wherein the optical fiber includes at least one dopant to facilitate a response to the nuclear radiation.

6. The radiation detection system of claim 1 wherein the optical fiber is capable of having at least one color center created therein in response to the nuclear radiation.

7. The radiation detection system of claim 6 wherein the optical fiber has color centers sensitive to respective frequencies of light from the light source.

8. The radiation detection system of claim 6 wherein the optical fiber has color centers sensitive to specific types of nuclear radiation.

9. The radiation detection system of claim 1 wherein the circuit is operative to detect a change in the rate of decrease in light carrying capacity of the optical fiber path.

10. The radiation detection system of claim 1 wherein the optical fiber includes a glass core and cladding material surrounding the glass core.

11. The radiation detection system of claim 1 wherein the optical fiber includes a glass core retained in the optical fiber path of a communal cladding material in the panel structure.

12. The radiation detection system of claim 1 wherein the panel structure includes a cladding material in which the optical fiber is disposed in the optical fiber path.

13. The radiation detection system of claim 1 wherein the panel structure includes a sheathing material enclosing the optical fiber disposed in the optical fiber path.

14. The radiation detection system of claim 13 wherein the sheathing material includes hard or abrasive particles or strands which if engaged by a tool bit breaching the panel structure will result in abrasion or breaking of the optical fiber.

15. The radiation detection system of claim 1 wherein the optical fiber is disposed in a communal cladding material about which is provided a sheathing material.

16. The radiation detection system of claim 1 wherein the panel structure has at least one radiation shielding sheet across a surface thereof to isolate radiation from extraneous sources.

17. The radiation detection system of claim 16 wherein the shielding sheet is disposed between the inside wall of the container and the panel structure to isolate the interior of the container from extraneous radiation sources outside of the container.

18. The radiation detection system of claim 16 wherein the at least one shielding sheet includes:

a first shielding sheet disposed between the inside wall of the container and the panel structure, and a second shielding sheet disposed on the inner side of the panel structure facing the interior of the container;

the first shielding sheet operative to block extraneous radiation outside of the container;

the second shielding sheet operative to block gamma rays and to allow passage of neutrons to be detectable by the optical fiber.

19. The radiation detection system of claim 1 further comprising:

a second annealing resistant optical fiber extending in an optical fiber path adjacent to the optical fiber path of the panel structure, the second optical fiber path extending across substantially the entire area of the panel structure to envelop substantially the entire volume of the container;

a first shielding sheet disposed between the panel structure and the second optical fiber and operative to block gamma rays and to pass neutrons;

a second shielding sheet disposed between the second optical fiber and the container wall and operative to block gamma rays and to pass neutrons;

the second optical fiber operative to detect neutrons;

a second optical fiber optically coupled to a second light source at one end and to a second light detector at the other end;

the circuit being connected to the light detectors and to provide discrimination between neutron and other forms of radiation impinging on the optical fibers.

20. The radiation detection system of claim 4 wherein the circuit is operative to determine from the rate of decrease in the intensity of light, the signature of radiation causing the decrease.

21. The radiation system of claim 20 wherein the signature of radiation causing the decrease is the half-life signature of an isotope of radiation causing the decrease.

22. The radiation detection system of claim 1 wherein the circuit is operative to compare the ratio of gamma radiation and neutron radiation and the ratio of emission energy per unit of time with stored radiation signature profiles for the identification of radioactive source material.

23. The radiation detection system of claim 1 wherein:

the panel structure has a plurality of optical fiber paths;

the light source is optically coupled to one end of each of the optical fibers for introducing light;

the light detector includes a light detector optically coupled to the other end of each of the optical fibers for receiving light from the respective optical fibers;

the circuit is connected to all of the light detectors and operative to compare the decrease in light carrying capacity of the respective optical fiber paths.

24. The radiation detection system of claim 23 including:

a second annealing resistant optical fiber extending in an optical fiber path across substantially the entire area of the panel structure to envelop substantially the entire volume of the container and providing a single continuous optical fiber path;

the light source including a light source coupled to one end of the second optical fiber for introducing light;

the light detector including a light detector optically coupled to the other end of the second optical fiber for receiving light from the second optical fiber;

the circuit including a circuit connected to the light detector coupled to the second optical fiber and operative to detect the decrease in light carrying capacity of the second optical fiber and to provide an indication thereof.

25. The radiation detection system of claim 24 wherein the circuit includes a circuit for comparison of the decrease in light carrying capacity of the optical fibers and to provide an indication thereof.

26. The radiation detection system of claim 1 wherein the optical fiber is enclosed in a neutron moderating material to slow neutrons to thermal energies impinging on the optical fiber from a radiation source.

27. The radiation detection system of claim 26 wherein the optical fiber includes a glass core and cladding material surrounding the glass core, and the neutron moderating material is in the cladding of the optical fiber.

28. The radiation detection system of claim 26 wherein the panel structure includes a sheathing material enclosing the optical fiber disposed in the optical fiber path, and the neutron moderating material is in the sheathing material of the optical fiber.

29. The radiation detection system of claim 1 wherein the optical fiber is a single mode fiber.

30. The radiation detection system of claim 1 wherein the optical fiber is a multimode fiber.

31. The radiation detection system of claim 1 further including a memory storing one or more profiles of radiation data;

the circuit connected to the light detector including apparatus for comparing the profile of light received from the optical path with profiles stored in the memory and for providing an output indication identifying the specific radiation impinging on the optical fiber.

32. The radiation detection system of claim 31 wherein the memory comprises a memory unit for storing data from various radioactive sources according to the half-life decay formula N=N_oexp(−

γ

t) which gives an identifying decay signature of the specific radioactive isotope.

33. The radiation detection system of claim 32 wherein the memory unit additionally stores data identifying the decay signature of any ensuing radioactive daughter isotopes created by the decay of the parent or original isotope.

34. The system of claim 1 wherein the optical fiber extends in a serpentine path across substantially the entire area of the panel.

35. The system of claim 34 wherein spacing between adjacent portions of the optical fiber is of a smaller size than a breach that could compromise the security of the container.

36. The system of claim 35 wherein spacing between adjacent portions of the optical fiber is sufficiently small to cause breakage or degradation of the optical fiber in reaction to an attempted breach of the panel.

37. The system of claim 1 wherein each of the plurality of liner panels is rectangular.

38. The radiation detection system of claim 1 wherein the light source provides light having a wavelength that enhances the sensitivity of the optical fiber to the radiation-induced change in the light in the optical fiber.

39. The radiation detection system of claim 1 wherein the light source provides light having a wavelength that is varied in accordance with the signature of the light received from the optical fiber path.

40. The radiation detection system of claim 1 wherein the light source provides light having a predetermined characteristic.

41. The radiation detection system of claim 40 wherein the predetermined characteristic of the light is one of sinusoidal, pulses, impulse waveforms and pulse trains.

42. The radiation detection system of claim 1 wherein the liner panels are integral with the container sides.

43. The radiation detection system of claim 1 wherein the optical fiber includes one or more dopants which enhance sensitivity of the optical fiber to the radiation induced change in the light in the optical fiber.

44. The radiation detection system of claim 1 wherein the entire enclosed volumetric space of the container, and the surrounding volumetric mass of the optical fiber constitutes a radiation detection system which totally encapsulates radioactive material in the container.

45. The radiation detection system of claim 1 including a telecommunication interface operative to transmit a detection signal from the circuit that indicates an alarm condition to one or more monitoring stations.

46. The radiation detection system of claim 31 wherein the memory stores profiles of radiation data on predetermined isotopes;

and

the circuit is operative to compare the profiles of radiation data on predetermined isotopes and to provide an output indication identifying the specific isotope of the radiation impinging on the optical fiber.

47. The radiation detection system of claim 31 wherein the memory includes a Fourier chip to store color center data, and to perform a Fourier analysis on measured color center data for comparison to stored color center data.

48. The radiation detection system of claim 1 wherein the optical fiber path provides a solid angle of emission of radiation from the nuclear radiation source and experiences a time integration of the emitted radiation impinging on the optical fiber.

49. The radiation detection system of claim 1 wherein the panel structure includes:

a plurality of liner panels each sized to line an interior wall of a respective side of the container, each of the liner panels having an annealing resistant optical fiber therein extending in a path across substantially the entire area of the panel, the optical fiber having a first end and a second end;

the light source includes a light source optically coupled to one end of the optical fiber of each of the liner panels and the light detector includes a light detector optically coupled to the other end of the optical fiber of each of the liner panels;

the circuit is operative to compare the intensity of the received light from all of the panels and provide an alert if at least one of the intensities of received light is different than the other intensities of received light.

50. The radiation detection system of claim 43 wherein the dopant is selected from the group consisting of gadolinium, isotope enriched gadolinium 157, boron 10 and lithium.

51. The radiation detection system of claim 1 wherein the circuit is operative to detect a change in an optical characteristic of the light from the light source transmitted in the optical fiber path.

52. The radiation detection system of claim 26 wherein the panel structure includes a resin material which bonds the panel structure to the inside wall of the container, and the neutron moderating material is in the resin material.

53. The radiation detection system of claim 46 wherein the circuit is operative to compare the profiles of radiation data on tagged isotopes and to provide an output indication identifying the specific tagged isotope of the radiation impinging on the optical fiber.

54. A radiation detection system comprising:

a support sized and shaped to enclosed substantially the entire volume of a protected space;

the support having an annealing-resistant optical fiber therein and extending in an optical fiber path across substantially the entire area of the panel structure to envelop substantially the entire volume of the container;

the annealing-resistant optical fiber having a first end and a second end;

the annealing-resistant optical fiber being reactive to nuclear radiation impinging on the optical fiber to cause a change in light carrying capacity of the optical fiber;

a light source optically coupled to one end of the optical fiber for introducing light;

a light detector optically coupled to the other end of the optical fiber for receiving light from the optical fiber; and

a circuit connected to the light detector and operative to detect the change in light carrying capacity of the optical fiber and to provide an indication thereof.

55. The radiation detection system of claim 54 wherein the circuit includes:

fail-safe circuitry that provides a fail-safe alarm signal in the absence of a signal from the light detector, irrespective of the cause of the signal absence.

56. The radiation detection system of claim 54 wherein:

the support includes a plurality of panels each having an annealing resistant optical fiber therein extending in a path across substantially the entire area of the panel, the optical fiber having a first end and a second end;

the light source includes a light source optically coupled to one end of the optical fiber of each of the panels and the light detector includes a light detector optically coupled to the other end of the optical fiber of each of the panels; and

the circuit is operative to compare the intensity of the received light from all of the panels and provide an alert if at least one of the intensities of received light is different than the other intensities of received light.

57. The radiation detection system of claim 54 wherein:

the optical fiber is reactive to nuclear radiation impinging on the optical fiber to cause a change in incremental slices of the optical fiber along the length thereof; and

the circuit is operative to detect the integrated effect of the change in the incremental slices.

58. The radiation detection system of claim 54 wherein the circuit is operative to discriminate radiation from the source in the enclosure from background radiation from inside or outside the enclosure.

59. The radiation detection system of claim 54 wherein the support has a plurality of optical fibers extending in a plurality of optical fiber paths across respective areas of the support;

and

the circuit is operative to distinguish anisotropic radiation from a source in the enclosure from isotropic radiation from background sources.

60. The radiation detection system of claim 57 wherein the circuit is operative to count the integrated effect of darkened incremental slices of the optical fiber along the length thereof, and compute the total volumetric attenuation of the light transmission in the optical fiber path.