Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
  • G01V5/00—Prospecting or detecting by the use of ionising radiation, e.g. of natural or induced radioactivity
  • G01V5/20—Detecting prohibited goods, e.g. weapons, explosives, hazardous substances, contraband or smuggled objects
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
  • G01N23/02—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material
  • G01N23/04—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material and forming images of the material
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2223/00—Investigating materials by wave or particle radiation
  • G01N2223/10—Different kinds of radiation or particles
  • G01N2223/101—Different kinds of radiation or particles electromagnetic radiation
  • G01N2223/1013—Different kinds of radiation or particles electromagnetic radiation gamma

Definitions

• the present invention relates to applications utilizing mono-energetic gamma-rays (MEGa-rays), and more specifically, it relates to techniques that utilize MEGa-rays for cnaracterizing isotopes.
• MEGa-rays mono-energetic gamma-rays
• MEGa-ray sources are created by the scattering of energetic (Joule-class), short-duration (few picosecond) laser pulses off of relativistic electron beams (several hundred MeV).
• the resulting scattered photons are forwardly directed in a narrow beam (typically milli-radians m divergence), are mono-energetic, tunable, polarized and have peak photon brilliance (photons/second/unit solid angle, per unit area, per unit bandwidth) that exceeds that of the best synchrotrons by over 15 orders of magnitude at gamma-ray energies in excess of 1 MeV.
• NRF nuclear resonance fluorescence
• T- REX/ FINDER MEGa-ray sources are ideal for this application and not only enable identification of isotopes but can also be used to determine the quantity and spatial distribution of isotopes in a given object In order to accomplish these tasks one analyzes the MEGa-ray beam transmitted through a particular object.
• NRF resonances are narrow, typically 10E-6 wide compared to the resonant energy, e.g., 1 eV wide for a 1 MeV resonant energy.
• MEGa-ray sources on the other hand are typically 10E-3 wide relative to their carrier energy, e.g., 1 keV wide for a carrier energy of 1 MeV.
• a given amount of (e.g., grams) of a resonant isotope removes a corresponding amount of resonant photons from a MEGa-ray beam, according to Beer's law.
• Detection or measurement of the absence of resonant photons in a MEGa-ray beam transmitted through an object can be thus be used to determine not only the presence of the material but also its location and its quantity. To do so requires a detector capable of resolving the number of resonant photons removed by the desired object from the MEGa-ray beam.
• Known gamma-ray spectroscopy technologies are not capable of resolutions better than 10E-3 in the MeV spectral region and are thus not able to accomplish the task.
• Bertozzi et al. (Bertozzi patent) envisions using a piece of the materia] under observation after the object in question to evaluate the removal of NRF resonant photons from the beam.
• Bertozzi suggestion uses a specific example/ namely the location of U235 hidden within a large container such as that used for a trans-oceanic commerce.
• the Bertozzi suggestion applies specifically to
• Transmission detector 14 is an energy collector mat measures the total gamma-rays passing through the object and the first detector 16, which consists of a piece (typically a foil) of the material/isotope that is being sought in the container, i.e., a foil 18 of U235 in this example.
• the foil of U235 in detector 16 is surrounded by a large area, gamma-ray spectrometer 20 that measures the spectrum of the photons scattered by the U235 foil 18. If U235 is present in the cargo container in quantities greater than a few grams, then the resonant photons will be removed from the interrogating gamma-ray beam and the gamma-ray spectrometer surrounding the foil of U235 will not see any resonant photons.
• FIG. IB shows a cargo container 30, that includes U235 material 32 that is interrogated by a
• polychromatic beam 34 that includes light resonant at the U235 line.
• spectroscopy of the scattered light shows only non-NRF photons and particles 36 and thereby reveals the absence of NRF photons and thus the presence of U235 material in the container. While this method in principle works, it has some significant limitations, in particular, it requires gamma-ray spectroscopy of the scattered photons to be ef ective. Gamma-ray spectroscopy is difficult and is accomplished in nearly all cases by collecting one gamma-ray at a time and analyzing the total energy of that photon. This can work for beams that have photons distributed evenly in time, e.g., those coming from a Bremsstrahlung source.
• Bremsstrahlung sources have been shown to be ill-suited for transmission based NRF detection schemes due to their wide bandwidth and beam divergence which are both ill-matched to NRF detection requirements (Pruit et al. paper).
• EGa-ray beams ate well suited to transmission detection due to their narrow bandwidth and low divergence (lOOx smaller than Bremsstrahlung); however, these sources by their nature produce large bursts of photons, up to 10E10 per pulse at rates of 10's to 100's of times per second.
• MEGa-ray sources are ill-matched to single photon counting based gamma-ray spectroscopy.
• NRF nuclear resonance fluorescence
• MEGa- ray s inverse-Compton scattering sources of mono-energetic gamma-rays
• FIG. 3A shows an embodiment of the present invention including a detector arrangement that consists not of two detectors downstream from the object under observation but instead three.
• the latter detector which operates as a beam monitor, is an integrating detector mat monitors the total beam power arriving at its surface.
• This transmission detector can, e.g., be identical to the latter detector in the Bertozzi scheme, which is described in US. 2006/0188060 Al, incorporated herein by reference.
• the first detector and the middle detector each include an integrating detector surrounding a foil.
• the foils of these two detectors are made of the same atomic material, but each foil is a different isotope, e.g., the first foil may comprise U235 and second foil may comprise U238.
• the integrating detectors surrounding these pieces of foil measure the total power scattered from the foil and can be similar in composition to the final beam monitor. Non-resonant photons will, after calibration, scatter equally from both foils, i.e., Compton, Delbruck, etc., and are not, to first order, dependent upon the number of nucleons in the isotope but are a function of the atomic element.
• the first foil will produce resonant photons as well as the non- resonant photons and scatter and thus more energy will emanate from the first foil than the second foil.
• a variety of methods for diagnosing the content of an interrogated object are provided herein and are within the scope of the present invention.
• the ratio of the energy scattered by each foil or the difference in energy scattered by each foil can be used to determine not only the presence of the material in the object under interrogation, but the exact ratio or difference is a function of the amount of material present, thus this detector arrangement can also provide
• Figure 1 A shows a prior art configuration in which a beam transmitted through a cargo container impinges upon two detectors.
• Figure IB illustrates light scattered by an interrogating foil.
• Figure 2A shows a cargo container that includes U235 material that is interrogated by a polychromatic beam that includes light resonant at the U235 line.
• Figure 2B illustrates a spectrum of scattered light showing only non-NRF photons and particles.
• Figure 3A shows an embodiment of the present invention including a detector arrangement that consists of three detectors downstream from a container having no U235 in the beam path.
• Figure 3B shows that for an object under interrogation that has no U235 present and the interrogating EGa-ray beam is tuned to the U235 resonant transition, then the foil will produce resonant photons as well as the non-resonant photons and scatter and thus more energy will emanate from the first foil than the second f oil.
• Figure A shows an embodiment of the present invention including a detector arrangement that consists of three detectors downstream from a container having U235 in the beam path.
• Figure 5 illustrates an example of the invention where, after exiting an object under test, a probe beam passes through a U238 foil and then through a U235 foil before propagating onto the beam monitoring detector.
• Figure 6A illustrates an embodiment that uses a single rotating foil.
• Figure 6B shows the two halves of the rotating foil of Figure 6A.
• Figure 7 is an example where a portion of a finite area MEGa-ray beam
• Figure 8 illustrates a finite area MEGa-ray beam that propagates through pixels of U235 material in line with pixels of U238 material.
• FIG. 3A shows an embodiment of the present invention where there is no U235 or U238 in the path of the beam.
• MEGa-ray probe beam 50 is tuned at a U235 NRF line.
• the path of beam 50 as it traverses container 52 does not intersect any U235 or U238 material.
• beam 50 After passing though container 52, beam 50 propagates to and through a first foil 54, which is surrounded by an integrating detector 56.
• beam 50 propagates to and through a second foil 58, which is surrounded by an integrating detector 60.
• beam 50 propagates onto an integrating detector 62.
• U235 foil 54 produces a larger amount of NRF than it would have if beam 50 had encountered U235 in its path through container 52. If a sufficient quantity of U235 had been present in the path of beam 50 within container 52, such that all of the resonant photons in beam 50 had been removed, men, after normalization of the signals at each detector to account for attenuation losses, the amount of non-resonant photons and scatter from foils 54 and 58 would have, to first order, been the same.
• FIG. 3A there is no U235 (or U238) within the beam path through the container, and therefore, in addition to the non-resonant photons and scattered particles, the integrating detector collects resonance produced by the interaction of probe beam 50 with the U235 in foil 54.
• Figure 3B depicts the signals produced by integrating detectors 56 and 58 in the example of Figure 3A.
• the elements of Figure 4A are identical in all respects to those of Figure 3A, except that a quantity of U235 material 62 is in the path of beam 50 as it passes through container 52. In this example, the amount of U235 is sufficient to remove all of the resonant photons from beam 50, such that there is no production of U235 NRF from foil 54, as depicted in Figure 4B.
• the present invention is capable of producing U235 NRF in foil 54 even in the presence of U235 within the path of beam 50 through container 52.
• the amount of U235 NRF produced by foil 54 is less than that produced when beam 50 encounters no U235 in its path through container 54, the amount of U235 that is produced is indicative of the quantity of that material in the path of beam 50.
• an image can be obtained of the U235 material within container 52.
• Other techniques for obtaining a 2D and 3D image are discussed below, and still others will be apparent to those skilled in the art based on the descriptions herein.
• the present invention uses examples for determining the presence, assay and image of U235, the present invention can be used for the same purposes in applications with other materials.
• FIG. 5 illustrates another example where, a ter exiting an object under test (not shown), a probe beam 70, passes through U238 foil 72 and then through U235 foil 82 before propagating onto the beam monitoring detector 90.
• the integrating detector 74 shown in cross-section, positioned near foil 72, is substantially similar, in this example, to the detector 84 positioned near foil 82. Integrating detector 74 is formed of a scintillator 76 and two photomultipliers 77 and 78. A Compton shield 79 is positioned between foil 72 and scintillator 76.
• FIG. 6A illustrates an embodiment that uses a single rotating foil rather mat the dual foils described supra.
• MEGa-ray beam 100 passes through rotating foil 102 and impinges on the integrating detector 106.
• An integrating detector 104 similar to the detectors 74 and 84 of Figure 5, is located near rotating foil 102.
• Figure 6B shows a front view of the rotating foil 102.
• one half 102' of the rotating foil comprises U235 and the other half 102" comprises U238.
• the beam 100 is pulsed at a fixed rate and the rotating foil 102 rotates at a fixed rate that is one half of the rate of pulses if beam 100. At such a rotational rate, the beam 100 will pass through the U235 portion in one pulse and in the next pulse, beam 100 will pass through the U238 portion.
• Figure 7 is an example where a portion of a finite area MEGa-ray beam 120 simultaneously passes through U235 piece 122 and U238 piece 124.
• the portion of beam 120 that passes through U235 piece 122 propagates onto integrating detector 126 and the portion of beam 120 that passes through U238 piece 124 propagates onto integrating detector 128.
• Figure 8 illustrates a finite area MEGa-ray beam 140 that propagates through pixels 141-146 of U235 material in line with pixels 151-156 of U238 material. This beam will completely cover any U235 material that has a diameter of less than the beam diameter. For example, if the beam diameter 140' is 1 cm and a U235 piece 148 has a diameter of .5 cm, then U235 piece 148 will be completely covered by beam 140.
• a separate integrating detector (not shown) is positioned to measure U235 NRF and non- resonant photons and particles for each of pixels 141-146 of U235 material and pixels 151-156 of U238 material.
• a separate integrating detector of integrating detectors 161-166 is positioned to measure the beam portion that passes through each pixel pair.
• the portion of beam 140 that passes through pixel 141 will then pass through pixel 151 and will propagate onto integrating detector 161.
• pixels 141-146 and pixels 151-156 are depicted as a two dimensional array, each pixel can be a part of an array of pixels extending perpendicular to the plane of the page to create a three dimensional pixel array.
• This exemplary configuration instantly provides a complete 2 dimensional image of any piece of U235 that is smaller than the diameter of beam 140. Such a beam can be moved relative to a larger piece of U235 to obtain an image of such piece.
• the beam and the piece of U235 can be moved relative to one another to obtain a 3 dimensional image of the U235.
• the beam and its alignment to the pixel arrays can be held constant as a unit, and the whole unit can be moved relative to obtain an image of the piece of U235.
• FIG. 29 To understand some exemplary methods for analyzing the data collected in embodiments of the invention, consider figures 3A through 4B.
• the MEGa-ray which is tuned to a U235 NRF line, passes through the container without encountering any U235. If the beam was not tuned to either the U235 or the U238 NRF line, the amount of signal collected by each integrating detector would be about the same. There would be some reduction in power by absorption and scattering as the beam propagates through the first foil. Therefore, the two signals are normalized. If the beam is then tuned to a NRF line of U235, the difference between the signal levels in each detector is produced by the NRF from the U235 content of the first foil. This difference will not change if the entire container is removed.
• the detection system can be set up and aligned and then targets, such as shipping containers, can be moved into the beam path. If the beam path does intersect material having U235 content / then the signal difference will be determined by the amount of U235 through which the beam passes. Placing this difference on a logarithmic scale will reveal small changes in the amount of U235 NRF produced signal collected by the integrating detector proximate to the U235 foil. This enables a variety of data analysis methods of varying degree of precision, For example/ simply measuring the amount of signal collected by the U235 detector on resonance before and during interaction with a U235 target will show a signal difference that is dependent on the amount of U235 encountered. In another example, as discussed supra/ a
• the signals can first be normalized a variety of ways, including the substitution of a U238 foil for the U235 foil / or by tuning the MEGa-ray beam to be of resonance.
• the difference between the two signals on the U235 resonance is dependent on the amount of U235 encountered.
• a difference is determined between (i) the ratio of the U235 detector signal to the third detector and (ii) the ratio of the U238 detector signal to the third detector. In each method, depiction of the results on a log scale reveals much smaller changes than on a linear scale.

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• 2009
  • 2009-07-21 US US12/506,639 patent/US8369480B2/en active Active
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