WO2007098493A2 - Détecteur de photons à panneau plat d'aire importante avec pixels hémisphériques et couverture totale de l'aire - Google Patents

Détecteur de photons à panneau plat d'aire importante avec pixels hémisphériques et couverture totale de l'aire Download PDF

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Publication number
WO2007098493A2
WO2007098493A2 PCT/US2007/062616 US2007062616W WO2007098493A2 WO 2007098493 A2 WO2007098493 A2 WO 2007098493A2 US 2007062616 W US2007062616 W US 2007062616W WO 2007098493 A2 WO2007098493 A2 WO 2007098493A2
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recited
photon detector
plate
scintillator
detector
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PCT/US2007/062616
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WO2007098493A3 (fr
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Daniel Ferenc
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The Regents Of The University Of California
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Publication of WO2007098493A2 publication Critical patent/WO2007098493A2/fr
Publication of WO2007098493A3 publication Critical patent/WO2007098493A3/fr

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
    • G01T1/16—Measuring radiation intensity
    • G01T1/18—Measuring radiation intensity with counting-tube arrangements, e.g. with Geiger counters

Definitions

  • This invention pertains generally to photosensors, and more particularly to a monolithic flat-panel photon detector including a matrix of hollowed hemispherical cells and interstitial reflectors.
  • Photon detectors are indispensable in many areas of fundamental physics research, particularly in the emerging field of particle astrophysics, as well as in medical imaging and nuclear nonproliferation monitoring.
  • Research in the area of high-energy physics and high-energy astrophysics is often based on the detection of Cherenkov or fluorescence photons emitted by charged particles in a wide variety of transparent media.
  • the interactions of neutrinos in transparent media create charged particles, which in turn radiate Cherenkov or scintillation photons that are detected as an indication of a captured neutrino. Therefore, efficient and sensitive photon detectors are the most important component of a neutrino telescope.
  • Photosensors play an equally important role in other diagnostic areas such as medical imaging, nuclear radiation monitoring and nuclear proliferation control. Photosensors are the only well proven active detector component to convert photons into electrical signals.
  • the best known photon detector in the art is the photomultiplier tube (PMT) developed by the 1960's.
  • the photomultiplier is a sensitive detector of radiant energy in the ultraviolet, visible and near infrared portions of the electromagnetic spectrum.
  • the photomultiplier tube consists of a photocathode, several dynodes and an anode within a glass vacuum tube. Photons striking the photocathode produce photoelectrons as a consequence of the photoelectric effect. The photoelectrons are directed by an electric field to an electrode or series of dynodes, each having a positive voltage greater that the previous one.
  • Secondary electrons are emitted by the first dynode and directed to a second dynode accelerated by an electric field. A greater number of electrons are produced from dynode to dynode and the electrons are eventually collected by an anode which provides a signal current pulse that is read indicating the presence of a photon.
  • vacuum photomultiplier tubes have shown some significant deficiencies in performance, have a limited capability of forming arrays, and are labor intensive and expensive to manufacture.
  • the PMT has a low photoelectron collection efficiency (at most -70% in large area PMTs) and a low quantum efficiency (20-25%), limited only to a narrow spectral region.
  • the PMT is not capable of resolving the number of photons in a photosensor pixel i.e. it does not have a single-photon resolution.
  • Photomultipliers also have a high sensitivity to magnetic fields, including the geomagnetic field of the Earth. Magnetic fields may divert the path of electrons and detection efficiency may depend on the orientation of the PMT in space.
  • Connector sockets may be unreliable in environments with high levels of moisture or vibration. Furthermore, parasitic currents and oxidized contacts may lead to spurious effects that are very difficult to track down. [0011] Accordingly, there is an increasing need for photosensor arrays with large detection surfaces and high sensitivity that are capable of mass production at relatively low cost. There is also a need for a photosensor array that is insensitive to magnetic fields or accidental exposure to ambient light and is strong and durable. The present invention meets these needs as well as others and is a significant improvement over the art. BRIEF SUMMARY OF THE INVENTION [0012] The present invention is a photon detector that is suitable for applications where low cost, industrial mass-production, extremely large quantities, high sensitivity, reliability and durability are essential. The photon detector shown in FIG.
  • FIG. 8 is particularly useful for photon detection in dense media like water, liquid scintillator, plastic scintillator, or ice. It provides excellent optical coupling in dense media, has low buoyancy, simple mounting, unique robustness, unprecedented stability in high ambient pressures (e.g. deep ocean deployment), virtual insensitivity to accidental exposure to high levels of light, and insensitivity to the geomagnetic field.
  • the preferred embodiment of the invention is a monolithic flat-panel vacuum enclosure with a transparent front plate having a matrix of hollow hemispherical cells cast into the vacuum side of the window plate.
  • the back plate may have matching hemispherical cells or may be a plain flat plate forming the second part of the evacuated enclosure.
  • the interior of the hemispherical cells is coated with a material to form a photocathode.
  • An electron detector or a scintillator is disposed at the center of the hemisphere preferably equidistant from all of the edges of the hemisphere.
  • each of the reflectors preferably provides space for placement of getter vacuum pumps to remove residual gasses.
  • the panel preferably includes a voltage plate in the middle that simultaneously distributes the anode and the cathode potentials to all pixels in the panel, creating an optimal electron lens in each pixel, together with the hemispherical cavities.
  • the 'vacuum part' of the detector transforms incoming photons into electrons in the photocathode layer, and compresses the signal to such a small area that a very small and inexpensive semiconductor sensor may be used for the electron detection.
  • the sensor may detect photoelectrons through the detection of scintillation light that the photoelectron creates in a small scintillator.
  • the incoming photons may also hit the hemispherical photocathodes indirectly after reflection from reflector cavities directing photons to the hemispherical cells and the photocathode.
  • a photoelectron (e) released by the photon (ph) from the photocathode is focused and accelerated to a small electron detector such as a fiber-coupled scintillator.
  • the amplified secondary light signal from the scintillator preferably travels via optic fiber out of the vacuum enclosure to a Geiger-mode Avalanche Photodiode (G-APD), where it is read-out and strongly amplified.
  • G-APD Geiger-mode Avalanche Photodiode
  • the photoelectron is detected directly by an electron detector such as an APD.
  • a photon detector is provided with a vacuum enclosure having a flat window plate with a matrix of hollow hemispherical-shaped cells cast into the vacuum side of the flat window plate, and a back plate.
  • the plates are sealed together.
  • the panel may have sides.
  • a photocathode is deposited within the hemispherical cells and a photoelectron detector at the center of each hemispherical cell is provided.
  • a voltage plate capable of holding an operational voltage across its thickness.
  • the voltage plate has a cathode surface and an anode surface that extends through the plate through a number of openings and a cathode surface.
  • the cathode surface has a resistor layer extending radially from the anode openings and the electric potential from anode to the cathode is gradually changed.
  • a photon detector has a preferably symmetrical vacuum enclosure having a first flat window plate with a matrix of hollow hemispherical-shaped cells cast into the vacuum side of the flat window plate, sides, and a second flat window plate with a matrix of hollow hemispherical-shaped cells cast into the vacuum side of the second window plate. Both sides of the panel are capable of detecting photons.
  • a photocathode is disposed within each of the cells.
  • a photoelectron detector is located at the center of each hemispherical cell.
  • a voltage plate capable of holding an operational voltage across its thickness is located under each window plate.
  • a photon detector is provided that is particularly suited for detection in optically dense media, such as water, liquid scintillator, plastic scintillator, or crystal scintillator.
  • optically dense media such as water, liquid scintillator, plastic scintillator, or crystal scintillator.
  • This is due the fact that light from such optically dense media may enter the panel through the glass window without significant losses or reflections, and proceed directly to the photosensitive photocathode area, or reach that area after one or more reflections from the mirror-coated cavities.
  • the nearly perfect optical coupling of the panel to dense optical media permits full angular acceptance, i.e. all photons (created in the coupled dense medium) will be detected, irrespective of angle of incidence of the photon to the panel.
  • FIG. 1 is a top view of a panel of one embodiment of a photon detector according to the present invention.
  • FIG. 2 is a cross-sectional view of the photon detector of FIG. 1 taken along the lines 2-2 of FIG. 1.
  • FIG. 3 is a cross-sectional view of the photon detector of FIG. 1 taken along the lines 3-3 of FIG. 1.
  • FIG. 4A and FIG. 4B depict the anode side and the cathode side of the high voltage plate of the embodiment shown in FIG. 1.
  • FIG. 5 is cross-sectional view of a symmetrical double sided embodiment of a photon detector using a photodiode as a photoelectron detector according to the present invention.
  • FIG. 6 is cross-sectional view of a symmetrical double sided embodiment of a photon detector using a scintillator as a photoelectron detector according to the present invention.
  • FIG. 7 is a cross-sectional view of FIG. 6 showing photon and electron paths.
  • FIG. 8 is a cross-sectional view of a schematic of a single tube photoelectron detector showing scintillator, fiber plate and Geiger-mode APD array.
  • FIG. 9 is a flow chart of the method for photon detection for amplifying photons.
  • FIG. 1 through FIG. 3 a single sided embodiment of the photon detector invention is shown.
  • the photon detector 10 depicted is preferably a hermetically vacuum-sealed flat-panel box, similar to a flat-panel TV screen, with a top window plate 14, a voltage plate 16 and an bottom plate 18.
  • the voltage plate 16 and the bottom plate 18 are separated by blocks 20 to create a thin chamber 22 that will permit the placement of wires or fiber optic cables beneath the voltage plate 16 and the top plate 14 and above bottom plate 18.
  • Sidewalls 12 or seals on the edges of the plates form an evacuated chamber.
  • Spacers 20 between the high-voltage plate 16 and the bottom plate 18 function to neutralize the outside mechanical force arising due to the atmospheric pressure on the window plate 14 and the bottom plate 18, or the higher ambient pressure in dense media.
  • the window plate 14 is preferably made of transparent dielectric material such as glass or quartz which is flat on the exterior side 24 exposed to the environment, i.e.
  • top plate 14 or bottom plate 18 are not limited in thickness so that the device can be adapted for use in pressure environments.
  • Bottom Plate 18 is preferably a flat glass plate that closes the panel structure from the opposite side of the window plate 14, and provides (together with the top window plate 14 and the side walls 12) hermetic vacuum sealing.
  • the hemispherical cavities 26 within the top plate 14 may have dimensions of essentially any value; however hemispheres ranging from a few millimeters to a few centimeters are preferred.
  • Each hemispherical cavity 26 forms a "Roman Dome" structure with strong "pillars” that give the panel a high mechanical stability. In higher ambient pressure applications, a rectangular, rater than a hexagonal pixel pattern, is preferred in that the rectangular pattern offers significantly stronger pillars.
  • a photocathode 30 is deposited on all hemispherical surfaces 26 of plate 14.
  • the photocathode 30 is backed up by a thin transparent conductive dielectric layer, such as ITO (Indium-Tin-Oxide), which establishes and maintains the photocathode potential.
  • ITO Indium-Tin-Oxide
  • any known photoemissive material can be applied to the interior of the hemisphere 26 to form the photocathode 30.
  • Alkali-antimonides materials have been shown to be suitable materials for the photocathode 30, for example.
  • Photocathode 30 materials may also be selected based on the spectral response of the material and the wavelength of radiation to be detected.
  • Composite patterns of cells with alternating types of photocathode material may also be formed.
  • plate 14 also has reflectors 28 that are shaped to reflect the incoming light onto the nearby hemispheres 26.
  • the reflectors are suitably shaped cavities that are placed between the hollow hemispheres. The light that is reflected by the reflectors 28 would otherwise have fallen between the photosensitive hemispheres 26.
  • the reflectors 28 therefore reduce dead area and provide high surface coverage.
  • the reflective surfaces of reflector 28 may be either a naked glass surface, i.e. a total internal reflector, or a surface coated with a metallic or dielectric reflective material.
  • the actual shape of the reflector 28 can vary but should take into account mechanical stress due to environmental pressure. If mechanical stress is not an issue then a shape that maximizes the angles of reflection onto the hemispheres is preferred.
  • the hemispheres 26 and the internal sections of the detector must have the air removed and the vacuum maintained within the panel.
  • optional "getter pumps" 32 are placed in the interior of the reflector cavities 28 as well as other areas and cavities except in the active photon detection volume of the hemispheres 26. For example, in one embodiment, getter pumps 32 are placed in the reflector cavities 28, on the anode surface of the voltage plate 16, and on the inner surface of the bottom plate 18.
  • Getters 32 may be in the form of evaporable getters, pre-evaporated getter films (deposited in vacuum before the final panel sealing), or non- evaporable getters (NEG). In most cases, except the pre-evaporated getter films, getters may be activated (and sometimes multiply reactivated) from the outside by inductive or laser heating and do not need any electrical feedthroughs. Getter pumps are provided to eliminate residual gases and maintain a vacuum within the panel through the lifetime of the detector. [0043] In the embodiment shown, optional passages 34 between the hemispheres 26 and the reflector cavities 28 with getters pumps 32, as well as the holes 36 through the voltage plate 16 allow the residual gas to reach the getter surfaces.
  • High-voltage plate 16 is a dielectric flat plate preferably made of glass and capable of holding the operational voltage across its thickness. The plate 16 brings simultaneously both the cathode and the anode potential to every pixel in the panel.
  • the cathode surface 38 of the high-voltage plate is the surface facing the photocathode 30 and the hollow hemispheres 26 of top plate 14.
  • the anode surface 40 faces the bottom plate 18.
  • the cathode surface 38 has two types of surfaces, a conductive surface and a resistive surface.
  • the high-voltage-transition area is a circular area underneath each hollow hemisphere which is covered with a resistive material 42 that gradually changes the electric potential from the anode potential 44 in the middle of each pixel to the cathode potential at the periphery 46 of each circular pixel. Electric contact is established between the resistive layer 42 and the conductive surface 46 that surrounds the resistive circular area.
  • the area 46 around the circular high-voltage-transition islands is a conductive material that electrically connects the photocathodes 30 of all the individual pixels in the panel to a universal cathode potential (not shown).
  • the anode surface 40 shown in FIG. 4B on the opposite side of the high-voltage plate from the cathode surface 38 is covered with conductive material over its entire area in order to distribute the universal anode potential to all the pixels in the panel through the holes 48.
  • the anode potential is transmitted through the holes 48 from the anode side 38 to the cathode side
  • Holes 48 in the high-voltage plate 16 are preferably located in the center of curvature of each hemisphere, which locally transmits the anode potential to the opposite side of the high-voltage plate in the middle of the high-voltage- transition area. [0047] Holes 48 also allow access of electron detectors as well as wires or optical cables for an electron sensor or scintillator through the high-voltage plate 16. Holes 36 enable residual gas circulation through the voltage plate 16 and access to getter pumps 32. [0048] An electron detector 50 is placed in the center of curvature of each hemisphere 26, in the middle of each pixel configured to receive photoelectrons from the photocathode 30.
  • the electron detector 50 may be an avalanche photodiode (APD), or a PiN photodiode, or a scintillator, or any other detector, capable of detecting electrons of energies of approximately 5- 35 keV in a vacuum.
  • Leads 52 may be wires if the electron detector 50 detects directly or a fiber optic cable if the electron detector 50 is a scintillator.
  • the scintillator crystal is covered with a thin layer of Aluminum or similar conductive metal. The Aluminum coating is needed both to establish the anode potential, and to prevent light feedback from the scintillator to the photocathode.
  • the coating may also provide a barrier against the evaporation of dopants from the scintillator, and absorption of gases from the environment by the crystal.
  • holes 48 be non-orthogonal holes to allow smooth fiber transition with a large bending radius of curvature. (See FIG. 6).
  • a readout feedthrough for the entire panel (not shown) is preferably placed on the side or the edge of the panel for exterior access, or in some other suitable place, depending on the application.
  • a single, compact feedthrough containing output lines 52 of all the pixels 50 in a panel is preferred. The output signals are transmitted from each pixel to the feedthrough by a separate optical guide or electric conductor 52.
  • Optical feedthroughs may be established either by direct hermetic placement of the optical guides into the panel wall, or indirectly, via transmission through a small prefabricated optical fiber coupling plate that is made as a part of the panel wall structure.
  • output signals may be received by direct light transmission from the vacuum side of the panel, with or without the aid of some collimating devices (cones and lenses).
  • each panel is connected to a voltage source through a single pair of connectors per panel.
  • the connector with the higher of the two potentials is connected to the anode side 38 of the high-voltage plate 16, and the lower potential connector is connected to the universal conductive surface of the cathode side 40 of the high-voltage plate 16.
  • FIG. 5 an alternative embodiment of the photon detector according to the present invention is shown.
  • the panel is fully symmetric, with identical dome-structured window plates on both sides, which provides ideal mechanical symmetry for applications in high- pressure environments. This is the preferred embodiment for applications requiring a high level of mechanical stability.
  • the panel 100 is composed of a first exterior plate 102 and a second exterior plate 104. These exterior plates are separated by a first voltage plate 106 and a second voltage plate 108 and blocks 110.
  • the cathode plane 112 of the first and second voltage plates are oriented under the hemispheres 114 of the vacuum side of the first exterior plate 102 and the second exterior plate 104.
  • the anode planes 116 of the first and second voltage plates 106, 108 face each other and are separated by blocks 110.
  • a photocathode 118 is disposed within each the hemisphere 114 of the vacuum side of the first and second exterior plates 102,104 and electrically coupled with the cathode side of the voltage plates 106,108.
  • the anode potential is transmitted through a hole centered below the hemisphere and surrounded by a circular shaped electrically resistive material on the cathode side of each voltage plate.
  • the high voltage plates 106, 108 simultaneously supply both the anode and the cathode potential to all of the pixels in the panel, and provide a continuous voltage divider within each pixel.
  • the high voltage plates 106, 108 preferably have the same structure as shown in detail in FIG. 4A and FIG. 4B.
  • Optical reflectors 120 are preferably formed from cavities in the exterior window plate 102 or 104 and are placed between the hemispheres 114 to reflect photons that would otherwise be lost in a dead area to the hemispheres 114 and provide nearly 100% coverage. Although cavities are preferred, other imbedded reflectors could also be used to reflect photons.
  • the optical reflector cavities 120 optionally include vacuum "getter” pumps 122 that help to remove residual gasses when the chamber, formed by sealing the exterior plates 102,104 and voltage plates 106, 108 and blocks 110, is evacuated. Residual gas or a compromised vacuum will result in inefficient or ineffective detection.
  • Electron detectors 124 are disposed in center holes of the voltage plates 106, 108 forming a readout network consisting of large diameter optical fibers coupled to scintillators. Alternatively, photoelectrons can be directly detected by PiN photodiodes or avalanche photodiodes (APD) or similar detector 124 as shown in FIG. 5.
  • APD avalanche photodiodes
  • the electron detectors 124 are scintillators and the optical fibers 126 run through the space between the voltage plates 106, 108 created by blocks 110.
  • the optical fiber 126 from each scintillator is preferably coupled to a Geiger-mode avalanche photodiode (G-APD) or to a G-APD matrix in the case of a large device.
  • G-APD Geiger-mode avalanche photodiode
  • the secondary sensors are placed outside of the vacuum enclosure in one embodiment. This results in a particularly simple and robust construction, without any electronic components enclosed in the vacuum panel dramatically simplifying thermal processing and reducing cross-contamination between the photocathode and the semiconductor sensor.
  • Photoelectrons originating from the hemispherical photocathode 118 are accelerated within the hemispherical vacuum tube 114 to an energy of approximately 5 to approximately 35 keV, and focused to a small scintillator surface 124.
  • the slightly amplified light signal from the scintillator is detected in a Geiger-mode APD array, placed outside the vacuum enclosure, on the other side of the fiber plate window that preserves the image configuration.
  • the double-sided panel comprises a fully symmetric multi-dome structure, ideal for applications in high-pressure environments. It may be sensitive to light on both sides, which is potentially very useful in many applications. If only one side of the panel is designed to be sensitive, the other side may be passive, but still shaped in the same way in order to play its important pressure-supporting role.
  • a photoelectron (e) released by the photon (ph) from the photocathode 118 is focused and accelerated to a small electron detector 124 (in the present case, a fiber-coupled scintillator).
  • the amplified secondary light signal from the scintillator 124 travels via fiber 126 out of the vacuum enclosure, to a Geiger- mode APD (not shown), where the signal is read-out and strongly amplified.
  • One significant aspect of the invention is the effective amplification of the photons. However, light amplification should not be confused with the final signal amplification. It can be seen that the structure of the device shown in
  • FIG. 1 through FIG. 7, will amplify the detected photons.
  • detection 130 of ambient photons can be improved by converting 132 the photons received by the apparatus to photoelectrons; focusing the photoelectrons on a scintillator 134 that creates many photons that can be transferred by an optical cable or directly detected by photodiodes or other detector, and detecting 136 the amplified light photon detector such as a photodiode. Electrical signals generated by the detector can be amplified if necessary at block 138.
  • the detected light is effectively amplified by the detection apparatus shown in FIG. 7 as follows:
  • Photocathode 118 converts a received photon to an electron.
  • An electron "lens” accelerates and focuses all the photoelectrons to a very small focal area covered with a scintillator 124.
  • the scintillator 124 emits many photons (hundreds to thousands) upon the electron impact.
  • the scintillator is coated on its front side by a very thin layer of aluminum that acts both as a shield against light feedback to the photocathode, and as electrical conductor to set up the large potential between the cathode and the scintillator.
  • the entire photosensitive area effectively maps to a very small active G-APD readout area (-1000 times smaller than the panel area).
  • This strong, more than 1000-fold concentration of information from the irreducibly large photocathode area to the readout device effectively bypasses Liouville's theorem by replacing a photon by a photoelectron, i.e. a charged particle that can be acted upon by an electrostatic field.
  • a photoelectron i.e. a charged particle that can be acted upon by an electrostatic field.
  • the light amplifier receives light on its entire front area and subsequently amplifies and concentrates the signal to the scintillator-optical fiber combination.
  • Another important function is the amplification of the light signal.
  • Use of a scintillator provides a light pulse that is significantly stronger than the intrinsic noise of the G-APD, i.e. at least 30 photons, when measured outside of the vacuum enclosure. This may be achieved by using a high light yield scintillator, and at least 15 kV of electron acceleration potential.
  • the G-APD will then itself provide the real signal amplification, typically a ⁇ 10 6 gain. Note that the light amplifier presents an ideal match between its vacuum part and the G-APD.
  • the two main disadvantages of G-APDs - the high level of intrinsic noise, and the small G-APD pixel size, are fully compensated by light amplification, and electron concentration, respectively.
  • G-APDs outside the vacuum enclosure leads to a simple and robust construction without any electronic components enclosed within the vacuum panel. This also prevents chemical cross-contamination between the photocathode and the silicon sensor. Since G-APDs are not an integral part of the flat panel, they could be upgraded at any time. More important, that would allow one to modify the position resolution of the panel, merely through remapping of G-APD pixels to a different number of primary pixels. This would allow production of a standard panel for all applications that require different resolutions.
  • the hemispherical photocathode configuration has many advantages over existing detectors.
  • the open hemispherical array architecture and the flat global structure are amenable to mass-production in continuous production lines techniques (like TV panels) including CMOS technology.
  • the open architecture allows the deposition of the photocathode, the conductive layers, and the getter layers from one side of the window plate in a production line (in contrast to the internal processing of PMTs, where the photocathode and the getter surfaces are created by deposition within the tube, using evaporators that are enclosed in the tube and remain there).
  • a second advantage is durability and safety against a catastrophic burnout with accidental exposures to strong light, since G-APDs may be safely exposed to ambient light while fully powered. Furthermore, the device is virtually insensitive to the earth magnetic field, both because the primary device, the vacuum Light Amplifier, is nearly unaffected by the earth magnetic field due to its high acceleration voltage, and G-APDs are completely insensitive to (even extremely large) magnetic fields. Flat panels also are perfectly suitable for high pressure exposure (deep ocean) - like in a classical dome architecture, the flat-to-hemispherical transition is ideal, particularly in a fully symmetric configuration.
  • a third advantage is a reduction in scale compared with the typical photomultiplier tube (PMT) permitting large arrays.
  • each pixel in the panel comprises one scintillator, coupled to an optical fiber, and one G-APD cell (1 x1 mm 2 ) located outside the vacuum enclosure (or just one APD inside the vacuum enclosure) rather than a 10-12- stage dynode system with an electrical feedthrough for each dynode stage, support structure in the vacuum, multi-pin connectors outside, and a HV resistive divider for each conventional PMT. Timing jitter due to nearly perfect electron focusing cannot be minimized in large area PMT's with classical dynodes, and a low acceleration potential in the first stage.
  • the apparatus also has a low storage and transportation volume and the panels are easy to mount and hold in large detection applications and experiments.
  • the cables for the electron detector readout, or optical fibers in the Light Amplifier configuration, are packed inside the panel and read out on the side. There is one small feedthrough for the entire panel and the readout coupling, either optical or electrical, is very small. Closely tiled flat panels may completely cover very large areas with very little dead area.
  • Another advantage is superior performance.
  • the structure provides for nearly 100% photoelectron collection efficiency which is normally a big problem in large area PMT's with secondary dynodes that results in lower and non-uniform photoelectron collection efficiency (at most -70% in large area PMTs). There is greater than 95% coverage area with virtually no dead areas on the panel.
  • Single-photon resolution superb in the light amplifier configuration with use of G-APDs.
  • the very strong signal amplification eliminates the need for expensive electromagnetic shielding or expensive preamplifiers.
  • the flat configuration is also good for production, spherical for time resolution, high voltage hold off, angular acceptance, uniform photocathode deposition, and collection efficiency.
  • the evacuated hemispherical configuration in conjunction with the continuous high-voltage divider, leads to spherical equipotential surfaces, without any edges or abrupt changes.
  • No insulators are present in the hemispherical cavity, only conductors and resistive surfaces. Insulators may charge up to the point where a flashover happens, while conductors and resistors eventually conduct away the surplus electric charge.
  • Example [0080] In order to demonstrate the light amplification function, a large single hemispherical vacuum enclosure was used rather than a flat panel with multiple cells.
  • the enclosure used was a spherical vacuum tube made of glass, 370 mm in diameter, with a bi-alkali photocathode deposited on the inside surface, and a flat 18 mm diameter focal area covered with a thin scintillator layer (blue light emitting scintillator Y 2 SiO 5 (Ce)), which is covered on top with a thin layer of Aluminum to prevent light feedback to the photocathode, and to establish the anode electrical potential.
  • a thin scintillator layer blue light emitting scintillator Y 2 SiO 5 (Ce)
  • the prototype had a 5 mm thick window which offered rather poor coupling efficiency, but still sufficiently strong for our proof-of-concept tests.
  • the one square millimeter G-APD was estimated to have received less than 0.7% of the photons emitted by the scintillator, with an average input light signal of five photons.
  • pulses corresponding to single photoelectrons were detected and individual photoelectrons were resolved within multi-photon events and groups of pulse amplitudes within well-defined multi-photon peaks.
  • one preferred scintillator design 150 within a single pixel vacuum tube includes a fiber plate 152 to couple the scintillator 154 to the G-APD array 156, both for an efficient coupling and for precise imaging.
  • Photoelectrons (e) originating from the hemispherical photocathode (not shown) are accelerated within the hemispherical vacuum tube, preferably to an energy of -25 keV, and focused to a small scintillator surface 154.
  • a thin layer of a conductive metal 158 is preferably applied to the scintillator 154.
  • the slightly amplified light signal from the scintillator is detected in a Geiger-mode APD array 156, placed outside the vacuum enclosure, on the other side of the fiber plate 152 window that preserves the image configuration.
  • the single tube embodiment can have a large photocathode area greater than that covered by a hemisphere.
  • the cathode area covers approximately 270 degrees or more with a corresponding spherical shaped scintillator disposed in the center of the tube. It can be seen that the photocathode can be applied to a spherical enclosure and receive and detect photons arriving at the detector from almost any direction in this embodiment.
  • This single-pixel device would provide almost full angular acceptance, a very large photosensitive area, perfect timing resolution, and 100% photoelectron collection efficiency. Its shape would be ideally fitted for deep- sea or ice neutrino telescopes. Using a matrix of G-APDs of fine granulation will not only significantly improve the position resolution, but also reduce the effective background noise. In particular, this will allow for a major improvement in deep-sea neutrino telescopes with the ability to discriminate weak optical light flashes from the ubiquitous background from 40 K decays and from the strong intrinsic PMT noise.
  • the panels of the present invention may be used in the mass-production of new, inexpensive, medical whole-body scanning devices for widespread use in functional imaging and diagnostics such as the gamma camera, SPECT scanners and PET (Positron Emission Tomography).
  • Other applications may include devices for the massive screening of cargo of all sizes and kinds for nuclear materials, passive gamma-ray detection, passive neutron detection, detection of gamma rays following neutron activation, detection of neutrons following induced or spontaneous fission in fissionable materials, detection of gamma-rays following induced or spontaneous fission in fissionable materials, gamma-ray Imaging of containers and vessels, gamma-ray imaging from a large distance, e.g. in ports, or from a large helicopter, truck, or ship.

Abstract

La présente invention concerne un photodétecteur avec une enceinte à vide à panneau plat avec une fenêtre comportant des cavités hémisphériques recouvertes d'un matériau de photocathode pour convertir les photons en photoélectrons. Les électrons sont focalisés depuis les photocathodes hémisphériques vers leurs centres où ils sont détectés dans de petits capteurs d'électrons. Des réflecteurs dans les aires mortes entre les hémisphères dirigent la lumière vers les photocathodes hémisphériques actives, ce qui permet une couverture totale de l'aire. Le résultat est que la totalité de la surface du panneau présente une détection active des photons, et que les informations sont concentrées vers une aire très faible des capteurs. Une plaque de tension distribue simultanément les potentiels d'anode et de cathode à tous les pixels du panneau. Dans un mode de réalisation, les photoélectrons sont détectés avec un scintillateur et des photodiodes à avalanche en mode Geiger (G-APD).
PCT/US2007/062616 2006-02-22 2007-02-22 Détecteur de photons à panneau plat d'aire importante avec pixels hémisphériques et couverture totale de l'aire WO2007098493A2 (fr)

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CN110954919A (zh) * 2019-12-13 2020-04-03 华中科技大学 一种面阵激光探测器的固定值噪声确定方法及去除方法
CN111522047A (zh) * 2020-03-24 2020-08-11 中国科学院紫金山天文台 一种星载空间光电转换模块和光电探测装置
US11460590B2 (en) 2017-08-03 2022-10-04 The Research Foundation For The State University Of New York Dual-screen digital radiography with asymmetric reflective screens
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US9064678B2 (en) 2010-05-14 2015-06-23 The Regents Of The University Of California Vacuum photosensor device with electron lensing
WO2015176000A1 (fr) * 2014-05-15 2015-11-19 The Regents Of The University Of California Appareil détecteur à grande surface pour photodétecteur, détecteur de rayonnement, et applications médicales de scanner à tomographie par émission de positons (pet)
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US11460590B2 (en) 2017-08-03 2022-10-04 The Research Foundation For The State University Of New York Dual-screen digital radiography with asymmetric reflective screens
CN110954919A (zh) * 2019-12-13 2020-04-03 华中科技大学 一种面阵激光探测器的固定值噪声确定方法及去除方法
CN111522047A (zh) * 2020-03-24 2020-08-11 中国科学院紫金山天文台 一种星载空间光电转换模块和光电探测装置
CN111522047B (zh) * 2020-03-24 2022-01-25 中国科学院紫金山天文台 一种星载空间光电转换模块和光电探测装置

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