Background Of Invention

This invention is concerned generally with an apparatus and method for sensing incident radiation and characterizing the radiation by generating an associated electronic signal for analysis. More particularly, the invention is concerned with an apparatus and method for sensing and characterizing incident electromagnetic radiation with good position or angular precision.

The detection and characterization of radiation has numerous commercial applications in modern society. For example, X-ray and neutron beams are scattered from and transmitted through materials in order to gain information about the structure and properties of the materials. X-ray machines are used to examine the contents of packages and suitcases as part of airline security measures. Numerous non-destructive testing procedures involve X-ray examination of components undergoing tests. Current technology used to implement these methods and apparatus have numerous deficiencies, such as, inadequate position or angular sensitivity, slow rate of analysis and testing, excessive cost of acquisition and maintenance of the equipment; and currently available equipment has large and bulky proportions that limit its scope of usefullness.

Brief Summary Of The Invention

It is therefore an object of the invention to provide an improved apparatus and method for sensing radiation.

It is another object of the invention to provide a novel apparatus and method for sensing radiation and characterizing the radiation in spatial or angular terms.

It is a further object of the invention to provide an improved method and apparatus for intensifying a detected radiation signal, while perserving angular sensitivity to the detected radiation.

It is an additional object of the invention to provide a novel apparatus and method for sensing radiation by activating a lasing mode in scintillator material and generating a signal characteristic of the intensity and relative angular position of the radiation.

It is another object of the invention to provide a method of manufacturing a device having high angular sensitivity for incident radiation.

In one aspect of the invention, the apparatus and method of operation enable the sensing of radiation by a micro-channel plate intensifier having a scintillator material disposed along. a substantial portion of the length of the channel plate openings. The intensifier plate surface a jacent the scintillator material is activated for generating a secondary electron signal responsive to the radiation incident on the intensifier plate surface. A phosphor containing layer is disposed within the channel plate at the distal end and coupled optically to the channel plate intensifier for generating light responsive to the secondary electron signal. Adjacent the phosphor layer is a charged coupled device for converting light from the phosphor layer into an electronic signal which is analyzed by signal processing equipment. In other forms of the invention a channel plate is not necessarily activated or an inactive channel plate is used in conjunction with an activated micro-channel plate to detect the radiation.

For the subject invention, it is further contemplated that the incident radiation can also be sensed and characterized by a device having a scintillator material adapted for undergoing lasing. A substantially reflective coating is placed on the radiation entry end of the scintillator material. A partially reflective optical coating is placed on the distal end of the scintillator material. Upon inputing sufficient power and frequency of radiation into the scintillator material, a laser beam output is generated; and this output can be used to characterize the incident radiation.

Further objects and advantages of the present invention, together with the organization and manner of operation thereof, will become apparent from the following detailed description of the invention when taken in conjunction with the accompanying drawings wherein like reference numerals designate like features throughout the several views.

Brief Description Of The Drawings

FIGURE 1A is a perspective view of a micro-channel plate arrangement and FIG. IB is a perspective view of a glass capillary array arrangement of one embodiment of the invention;

FIGURE 2 is a cross sectional view taken along line 2-2 in FIG. 1A;

FIGURE 3A is a plan view of a charge coupled device; FIG. 3B is an assembly of the micro-channel plate of FIG. 1A and the charge coupled device of FIG. 3A; and FIG. 3C is a cross sectional view taken along 3C-3C in FIG. 3B;

FIGURE 4 is a component block diagram of a detection system for both sensing incident radiation and manipulating the measured signal;

FIGURE 5 shows a perspective view of a fiber bundle arrangement in another form of the invention;

FIGURE 6 shows a side view of a preferred form of high density assembly of scintillator elements in a detection device; and

FIGURES 7A and 7B are combination structure/process flow diagrams illustrating two different methods of manufacturing a position and angularly sensitive radiation detection device.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

One form of a position and angularly, sensitive detection device 10 (hereinafter, "detection device 10") for sensing and characterizing radiation incident thereon is indicated generally in FIGS. 3B, 3C, 4 and 6. The detection device 10 includes means for channeling the incident radiation 12 into well-defined detector channels 14 in order to measure with precision various angular or positional information about the incident radiation 12. The channeling means can, for example, be constructed from various conventional components (to be described in detail below) having a large number of the detector channels 14 for defining angular or positional ranges for the incident radiation 12. The incident radiation 12 can, for example, include beams of X-rays, neutrons, electrons, ions, molecules and fission fragments.

The detection device 10 is utilized as part of a detection system 13 shown generally in FIG. 4. The detection system 13 manipulates the signal received from the detection device 10 and provides output data to the user. Further operational details of the detection system 13 will be provided after explaining particulars of the detection device 10.

Conventional channel type components used to construct the detection device 10 can include glass capillary arrays,

icro-channel plates (such as, a Channeltron device manufactured b_y Gallileo ElectroOptics, Inc.) or other finely divided structural components having channels arranged in a two-dimensional matrix. The transverse cross section of a micro-channel plate is typically circular as shown in the perspective view of FIG. 1A, while a glass capillary array can have a square cross section as in FIG. IB. The longitudinal geometry of the detector channels 14 can take on various forms, such as, for example, straight, curved, or combinations thereof. In some applications the detector channels 14 are disposed in a "chevron" type of arrangement with straight angle portions in one layer of the detector channels 14 and the adjacent channel layers having oppositely angled straight portions (mirror image angles across the boundary plane between different layers). In the preferred configurations of the invention, channel continuity is maintained in order to preserve the ability to characterize the incident radiation 12 in terms of the angle of incidence or relative sensed position on the matrix of channels. In the case of using micro-channel plates, a single micro-channel plate (see FIG. 1A) is generally best for resolution purposes. If multiple micro-channels plates are used, the spacing between sections should be minimized in order to avoid angular spreading of the channel signals. An electrically insulating medium, such as a vacuum is, however, usually required between sections.

In the preferred embodiment the geometric arrangement chosen for the detector channels 14, therefore, not only must be capable of detecting the radiation 12, but also must be able to characterize the angle of incidence or relative position of the radiation 12. The above discussed geometries, and combinations thereof, can achieve these objectives and further details of the detection device 10 are set forth hereinafter. •

SUBSTITUTE SHEET

The manner of detection of the radiation 12 varies depending upon the choice of the type of the detector channel 14 (glass capillary array or micro-channel plate, for example) . One of the choices of the detector channel 14 is a channel plate intensifier, such as an activated micro-channel plate 15 which intensifies the signal (see FIG. 1A and the cross sectional view of FIG. 2). The radiation 12 is sensed when it strikes one of the active areas of the micro-channel plate 15, as opposed to an inactive intervening web area 19. The active areas include a channel surface layer 16 which is typically a doped semiconductor. The channel surface layer 16 generates a high gain secondary electron signal responsive to the radiation 12, and the resulting secondary electrons are emitted from the channel surface layer 16, undergo multiplication and are attracted to the output anode end of the detector channel 14 with the anode maintained at an appropriate potential energy (typically, +1 to +3 kilovolts) .

To enhance production of the secondary electron signal from the activated micro-channel plate 15, a substantial length of the detector channel 14 is filled with a scintillator material 17 (shown as dotted regions in FIGS. 1A and 2). The scintillator material 17 itself can include, for example, Nal (Th) , Csl (Th) , Cd O. , Bi.Ge.0-_ and even polymeric materials. The volume in the detector channel 14 chosen for the scintillator material 17 allows conversion of a large fraction of the radiation 12 into the desired secondary electrons. In the same manner as the radiation 12 can directly generate secondary electrons, the photons 18 generated in the scintiliator material 17 strike the channel surface layer 16 to generate a secondary electron signal to be collected at the output anode end. The secondary electrons .are emitted from the channel surface layer 16 and a cascade "C" of further secondary electrons are generated in the vacuum region- between the

scintillator material 17 and the anode end of the detection device 10. Due to the large significant multiplication or gain factor ari .si.ng from the acti.vated surface layer 16 (104

10 gain, typically), the signal to noise ratio is much higher than direct detection of the radiation 12.

The secondary electron signal generated by the channel surface layer 16 is then collected by means for generating light. The light generating means, such as a phosphor layer 22 shown in FIG. 2, is positioned within the detector channel 14 adjacent the anode end of the micro-channel plate 15 and converts the secondary electrons into light. Suitable phosphors are Pll (ZnS (Ag) @ 460nm) or P20 [(Zn, Cd) S (Ag) @ 560nm wavelength] which are available from GTE Sylvania, Towanda, Pa. The light generated is then output to conversion means, such as a charge coupled device 24 shown alone in a top view in FIG. 3A, coupled to the device 24 in FIG. 3B and in cross section with the micro-channel plate 15 in FIG. 3C. Note the charge coupled device 24 is shown as a square matrix of active sensing areas 21 of approximately the same size as the cross sectional area of the scintillator material 17 in the detector channels 14. Other geometrical arrangements are possible for the charge coupled device 24, such as a linear array. The charge coupled device 24 generates an electronic signal for analysis. The charge coupled device 24 can, for example, be a Fairchild CCD 122 or other such conventional charge coupled device. Preferably, the wavelength output of the phosphor layer 22 is matched to the wavelength sensitivity of the charge coupled device 24 in order to optimize signal output for analysis.

As indicated hereinabove, the phosphor layer 22 is disposed within the detector channel 14 and the active, separate areas of the charge coupled device 24 are about the size of the active area of each of the detector channels 14.

T ese features are provided in order to preserve the angular, or positional, characteristics of the sensed incident radiation 12. As mentioned hereinbefore, precise angular or positional information is achieved by maintaining spatial continuity between the detector channel 14, the phosphor layer 22 and the charge coupled device 24. Therefore, the distal end of each of the detector channels 14 (containing the phosphor layer 22) is positioned adjacent a similar sized area, or at least an associated region, of the charge coupled device 24 to maintain continuity and a clear association to selected elements of the charge coupled device 24. Precise angular or positional information for the incident radiation 12 can therefore readily be obtained by virtue of calibration methods for establishing precise angles and/or positions for the incident radiation 12. For example, a known image shape or pattern can be transmitted onto or scanned by the detection device 10. The measured electronic signal from a known standard shape can then be used to establish the shape or pattern of an unknown. In a similar manner a standard X-ray diffraction pattern can be applied to the detection device 10 to establish various diffraction angles relative to 0° (forward) scattering.

The measured electronic signal generated by the charge coupled device 24 is output to the remainder of the detection system 13 (see FIG. 5) for manipulation and output to the user. An electronic signal 23 is output from the charge coupled device 24 to an amplifier 25 (such as, a Fairchild CCD 122 DB circuit board with amplifier) which accepts the electronic signal 23 on a timed basis using the illustrated clock signal 27. A power supply 29 (such as, a SOLA 81-12-215-01) provides fifteen volts DC power to the amplifier 25. The amplified electronic signal 31 is output in a time controlled, clocked manner by a signal generator 33 (such as Tektronix TM503) to an oscilloscope 35 (such as a Gould OS 4000

unit). The amplified electronic signal 31 is output to an X-Y recorder 37 (such as, an HP 7045A unit) which generates a hard copy for the user.

In another embodiment of the invention, the array of the detector channels 14 can take the form of a capillary array 39 (as shown in FIG. IB), such as a commercially available glass capillary array having square cross sectional areas for the detector channel 14. Such forms of the glass capillary array are available from Collimated Holes, Inc., Cambell, Ca. This type of array is generally an inactive material and can be used as the matrix for containing the selected scintillator material 17. In this embodiment the scintillator material 17 generates the photons 18 responsive to the incident radiation 12. The reflective layer 20 on all the longitudinal surfaces of the detector channel 14 (shown on two of the longitudinal surfaces in the phantom perspective view of one of the detector channels 14 in FIG. IB) insures substantially all the photons 18 are collected at the distal end of the detector channel 14. One can also construct the capillary array of a material having an index of refraction less than the scintillator material. Thus, the walls of the capillary array act to reflect the photons back into the scintillator material and enable maximizing the electronic signal 23 through collection of substantially all the photons 18. In a similar manner as for the micro-channel plate arrangement of FIGS. 1A, 2 and 3, these collected photons 18 are then output to the charge coupled device 24 for generation of the electronc signal 23. Note in this embodiment there is no need for the phosphor layer 22 since there is no secondary electron signal which does arise in the activated micro-channel plate 15 arrangement discussed hereinbefore.

The scintillator material 17 used to sense the radiation 12 can be disposed within the various possible

channel type components by different methods, such as, for example, hot forging the scintillator material 17 into the detector channels 14 or growing the material within the detector channels 14. The channel component and the scintillator material 17 (or other material, such as polymeric materials) should be chosen to allow placement of the scintillator material 17 in the channels 14 without: (1) loss of integrity of the channel matrix and (2) also without substantially diminishing the effectiveness of the scintillator material 17 to convert the incident radiation 12 into a collected electronic signal. For example, in the case of an inactive capillary array, the array can be constructed of a glass, ceramic or cermet having a softening point above the temperature of hot forging of the selected scintillator material 17. For active channel plate embodiments of the invention, the doped semiconductor surface layer is, for example, a doped lead oxide with a softening point greater than that of the subject scintillator material 17.

In a preferred form of the invention the scintillator material 17 comprises a much larger percentage of the active area, as compared to the fifty to seventy percent typically present for the micro-channel plates 15 or the glass capillary array 39. Ideally, the assembled form of the detection device 10 would be based on a matrix constructed from linear arrays of regular shaped (such as square or hexagonal cross sectional area) coupled lengths of the scintillator material 17 (see FIG. 6). The longitudinal outer surfaces of each section of the scintillator material 17 is coated with the reflective layer 20. Coupled to the distal end of each section of the scintillator material 17 is the charge coupled device 24 for

generating the electronic signal for analysis. Example methods for constructing such a dense packed arrangement of the scintillator material are set forth hereinafter.

In another form of the invention the matrix forming the detection device 10 can take the form of a plurality of scintillator crystal fibers 30 shown in FIG. 5. These fibers 30 are bundled together, and each of the fibers 30 has been coated with a reflective layer (not shown) . The reflective layer is used to insure the photons 18 created by the incident radiation 12 are not lost and are eventually converted into the desired electronic signal. The distal end of the scintillator crystal fibers 30 is disposed adjacent a charge coupled device 34 (shown in an exploded view in FIG. 5) for converting the photons 18 into the electronic signal 23 for analysis. If an application results in conditions adverse to charge coupled devices, one can couple optical fibers directly to the scintillator crystal fibers 30 to remove the charge coupled device 34 from the offending environment.

The manufacture of one embodiment of the preferred form of the detection device 10 is shown in FIG. 7A. This method allows production of the dense packed scintillator elements as described hereinbefore. The method begins by preparing for treatment the upper and lower surfaces of a scintillator crystal 44. Preliminary steps can, for example, include mechanical and/or chemical polishing steps and preparing a selected region on an upper surface 45 for an etching step. As shown in FIG. 7A, the etching step produces separate channel portions 46 in the scintillator crystal 44 on the upper surface 45. The etching can, for example, be performed by an energetic beam, (such as, for example, an ion or laser beam) or by placing a mask 43 on the upper surface 45 and chemically etching the exposed area. In the case of Cd WO., the preferred method is etching by means of a laser

SHEE

beaiti, such as, by an excimer laser. After completing the etching step to form separate channels 46 (and removing the mask 43, if used), an optically reflective and X-ray absorbing coating 48 is deposited on the upper surface 45 and on the surfaces in the open regions between the channel portions 46 of the scintillator crystal 44. The various exposed coatings are then planarized by a conventional process, such as by chemical or mechanical means, by an energetic beam or by plasma etch processing. A support structure 50 is coupled to the upper surface 45 by an adhesive or other conventional means, such as diffusion bonding or ultrasonic welding. A portion of the bottom of the scintillator crystal 44 is then removed to expose the channel portions 46 and the coating 48 thereon. The remaining exposed surfaces, except the proximate end, of the scintillator crystal 44 are coated with an optically reflective and X-ray absorbing coating 52. The sides of the coated scintillator crystal 44 are then coated or encapsulated and machined, or otherwise prepared, to enable coupling the separate channels 46 to a charge coupled device (not shown in FIG. 7A) .

The proximate end of the scintillator crystal 44 is prepared and cleaned and an optically reflective and X-ray transmissive coating (such as aluminum) is applied to a proximate end of the scintillator crystal 44, leaving the distal end uncoated or an optically transmissive coating thereon. To enable coupling the separate channels 46 to the charge coupled device one can also use an optical medium (not shown), such as a Dow Corning silicone grease (n*=1.5) or refractive liquid (n«1.4 to 1.8, such as, Cargille No. 5763 with n=1.63) or solids with an index of refraction greater than 1.8. If the scintillator crystal 44 is CdWO. (n is approximately 2.2) or Bi. Ge^ 0._ (n is approximately 2.1), careful selection is required of the optical coupling

medium in order to optimize the electronic signal by minimizing losses and internal reflections.

Another method of manufacture shown in FIG. 7B involves preparing a scintillator crystal layer 56 and depositing an optically reflective and X-ray absorbing layer 58 on the scintillator crystal layer 56. These two steps are repeated to form a plurality of alternating layers of the scintillator crystal layer 56 and the optically reflective and X-ray absorbing layer 58. The number of such alternating layers is determined by the size of the matrix ultimately desired by the user. The assembled plurality of alternating layers are then sectioned perpendicular to these layers to provide a series of cross sectional slices. In these slices are a stack of the scintillator material 56 and alternating optically reflecting layers 58 therebetween. These sectioned pieces are then processed by depositing optically reflective and X-ray absorbing coatings 60 (shown as reverse cross hatch areas in step 4 of FIG. 7B) on the longitudinal surfaces. Then, one can deposit an optically transmissive layer 61 on, or leave clear, on the distal end of the sectioned scintillator material 56. An optically reflective and X-ray transmissive layer 62 is also deposited onto the proximate surfaces of the scintillator material 56. This step can then be followed by using these processed assemblies of sectioned and coated scintillator material 56 as building blocks to form a bundle or matrix for carrying out the intended function of the detection device 10.

In another form of the invention the detection device 10 is constructed to undergo lasing action responsive to the appropriate power and frequency of the incident radiation 12. This construction enables substantial improvement in certain signal characteristics, such as, signal to noise ratio and sharpened energy and time output for the

STITUTE SHEET

electronic signal 23. This lasing action is accomplished by use of the proper (and conventional) geometry (see FIG. 6) for εcintillator/laser material 17. This geometry includes a substantially reflective layer 40 on the radiation entry face of the crystal material 17, and a partially reflective layer 42 is disposed on the distal end to allow passage of the laser light. Therefore, given the appropriate energy and/or frequency input into the material 17, lasing action can occur in response to the incident radiation 12; and the intensity and angular or positional information of the radiation 12 can be character. zed.

While preferred embodiments of the present invention have been illustrated and described, it will be understood that changes and modifications can be made therein without departing from the invention in its broader aspects. Various features of the invention are defined in the following claims.