JP5152950B2 - Microchannel plate, gas proportional counter, and imaging device - Google Patents

Description

  The present invention relates to a microchannel plate, a gas proportional counter, and an imaging device.

  In recent years, a new type of detector has been developed in which a lead glass capillary plate that functions as a micro channel plate (MCP) is operated as an imaging type gas proportional counter (CGPC). Non-patent documents 1 to 8). Recently, as another radiation detector capable of detecting a two-dimensional position of X-rays or the like, a gas electron multiplier (GEM) has attracted attention (see Non-Patent Documents 10 to 12). ).

Furthermore, the present inventor has further improved the conventional CGPC, a capillary plate capable of sufficiently reducing the noise level, a new CGPC using the capillary plate (Patent Document 1), and impact resistance and handleability compared to GEM. And CGCP (Patent Document 2) with improved uniformity of sensitivity distribution.
H. Sakurai et al., "A new type of proportional counter using a capillary plate", Nucl. Instr. And Meth. In Phys. Res. A374 (1996) 341-344. H. Sakurai et al., "Characteristics of capillary gas proportional counter", SPIE Proceedings Reprint, vol. 2806 (1996) 569-576. H. Sakurai et al., "Detection of photoabsorption point with capillary imaging gas proportional counter", IEEE Trans on Nucl. Sci. Vol. 49, No. 3, (2002). M. Tsukahara et al., "The development of a new type of imaging X-ray detector with a capillary plate", IEEE Trans on Nucl.Sci.vol.49, No.3, (1997) 679-682. H. Sakurai et al., "The form of X-ray photoelectron tracks in a capillary gas proportional counter", IEEE Trans on Nucl.Sci.vol.46, No.3, (1999) 333-337. H. Sakurai, "Imaging gas proportional counter with capillary plate", Radiation vol.25, No.1, (1999) 27-37. H. Sakurai et al., "New type of imaging X-ray detector using a capillary plate", SPIE Proceedings Reprint, vol. 3114 (1997) 481-487. T. Masuda et al., "Optical imaging capillary gas proportional counter with penning mixture", IEEE Trans on Nucl.Sci.vol.49, No.2, (2002) 553-558. Nishi, Yu .; Tanimori, Y .; Ochi, A .; Nishi, Ya .; Toyokawa, H., "Development of a hybrid MSGC with a conductive capillary plate.", SPIE, vol.3774 (1999) 87-96 . F. Sauli, Nucl. Instr. And Meth. A 368 (1977) 531. FAF Fraga, et al., Nucl. Instr. And Meth. A 442 (2000) 417. D. Mormann, et al., Nucl. Instr. And Meth. A 504 (2003) 93. JP 2004-241298 A JP 2005-32634 A

Here, a schematic configuration of an imaging apparatus using CGCP will be described taking an imaging X-ray detection apparatus as an example. The imaging X-ray detection apparatus usually has a configuration in which an optical system and an imaging system are connected in sequence in the subsequent stage of the CGCP. The CGCP is installed inside a chamber in which a beryllium window into which electromagnetic waves such as X-rays are incident is provided at one end and a light transmission window is provided at the other end. CP is a thin plate member in which a plurality of hollow lead glass capillaries having a diameter of about 100 μm are integrated, and thin film electrodes are formed on both surfaces thereof. Further, a shaping ring connected to the power supply and the installation potential is provided in the front stage (photocathode side) of CP, and a drift region is defined. In the chamber, a mixed gas in which trimethylamine (TMA) or the like having a Penning Effect is added to Ar gas or CH ₄ gas as a main component is enclosed.

When X-rays are incident on the imaging X-ray apparatus configured as described above through the beryllium window, the X-rays interact with gas molecules existing between the beryllium window and one surface (CP _IN ) of the CP facing the beryllium window. Then, high energy primary electrons (X-ray photoelectrons) are emitted by the photoelectric effect. The primary electrons travel while applying energy to another gas, and an electron-ion pair is generated in the track to form an electron cloud that enters the capillary from one side of the CP (CP _IN ). To do. An electric field of, for example, 10 ⁴ V / cm or more is formed inside the capillary. Electrons collide with gas molecules one after another to cause gas discharge and excitation light emission, and electron multiplication (for example, 10 ³ to 10 ^4). Times) and photoproliferation. The amplified light passes through the light transmission window, enters the optical system, and is guided to the imaging system.

  When using such an imaging X-ray detection apparatus, the present inventor appropriately selects two different modes, a so-called high luminance mode and a high resolution mode, according to the application, using the characteristics of CGCP. Are operating.

That is, the high luminance mode is a normal operation mode in which a forward bias voltage is applied so that the electron cloud moves (drifts) in the direction in which the electron cloud is drawn toward the CP side in the drift region between the beryllium window and CP _IN. . In this case, since the entire electron cloud generated by the primary electrons can enter the CP, extremely high brightness (sensitivity, X-ray detection efficiency) is achieved. However, since the probability that the electron cloud is diffused when traveling in the gas increases, the X-ray incident position information tends to be lost, and the resolution characteristics (position resolution) tend to be slightly inferior.

  On the other hand, the high resolution mode is an operation mode in which a reverse bias voltage is applied in a direction in which the electron cloud moves (drifts) in the drift region so that the electron cloud moves toward the beryllium window, as opposed to the high luminance mode. According to the knowledge of the present inventors, the reason why high resolution can be achieved by applying such a reverse bias voltage is estimated as follows.

In other words, a long primary electrons projected range generated in the drift region, and the electron cloud generated in the course progression thereof, so are prevented to enter the CP by a reverse bias voltage, within the capillary CP, with CP _IN vicinity The generated electron cloud enters and participates in electron / photoproliferation. Since the electron cloud generated in the vicinity of CP _IN has a short distance to the CP, the electron cloud is hardly diffused in the gas and can enter the capillary near the position where the electron cloud is generated. As described above, since only the electron cloud that holds the X-ray incident position information substantially without diffusing contributes to the electron / photo multiplication in the capillary, the position resolution is determined by the capillary diameter itself. obtain.

  However, the high-resolution mode that applies reverse bias voltage in this way is excellent in resolution characteristics, but a large amount of electrons (clouds) generated in the drift region do not enter the capillary, contributing to electron / photoreproduction in the capillary. The number of electrons to be reduced tends to decrease the brightness (sensitivity, X-ray detection efficiency).

  Therefore, the present invention has been made in view of such circumstances, and an object thereof is to provide an MCP, a gas proportional counter, and an imaging device having excellent characteristics capable of simultaneously achieving both high luminance and high resolution. And

  In order to solve the above problems, the MCP according to the present invention includes a base having a plurality of through holes and having an insulating property, and is mainly disposed in a gas atmosphere containing an inert gas to constitute a proportional counter. The substrate has a photoelectric conversion part provided on at least the inner walls of the plurality of through holes. Here, as long as the photoelectric conversion unit is formed on the inner wall of the through hole (that is, the inner surface of the through hole), for example, the photoelectric conversion unit may be provided also on the surface of the base around the open end of the through hole.

  In the MCP configured as described above, a plurality of through-holes function as microchannels for performing electron / photo multiplication in a state where an electric field is formed by applying a voltage to both end faces of the substrate. The inventor makes an MCP having such a configuration as a prototype, and uses it instead of the CP of the imaging X-ray detection apparatus described in Patent Document 1, for example, and applies the above-described reverse bias voltage to the “high resolution mode” As a result, it was confirmed that a luminance comparable to that of the above-described “high luminance mode” was achieved while sufficient resolution characteristics were obtained.

  In addition, this MCP configuration is modeled and X-rays, gas, and CP are used using the EGS4 code (The EGS4 Code System by WR Nelson, H. Hirayama and DWO Rogers, SLAC-265, Stanford Linear Accelerator Center, 1985). Monte Carlo simulation of interaction with material materials was performed to evaluate detection efficiency and pulse height spectrum (distribution).

  As a result, when an MCP having a photoelectric conversion part provided on at least the inner walls of the plurality of through holes (inner surfaces of the through holes) is used, in particular, 10 keV or more as compared with an MCP having no such photoelectric conversion part. It was confirmed that the detection efficiency with respect to X-rays having the following energy is significantly increased.

  Furthermore, the present inventor has modeled the three-dimensional configuration of MCP, and has developed Maxwell 3-D Field Simulator (Commercial Finite Element Computation Package, Ansoft Co. Pittsburg, PA, USA.) And Garfield (R. Veenhof, Nucl. Instr. and Meth. A 419 (1998) 726. HYPERLINK "http://garfield.web.cern.ch/garfield/" http://garfield.web.cern.ch/garfield/) The simulation of was carried out. The electric field was calculated with Maxwell, and the motion of electrons in the gas was calculated with Garfield. As a result, the electron cloud generated in the drift region in front of the through hole tends not to enter the inside of the through hole having the photoelectric conversion portion provided on at least the inner wall of the through hole (the inner surface of the through hole). It turned out to be.

  Thus, in the MCP having the photoelectric conversion portion provided on at least the inner walls of the plurality of through holes (inner surfaces of the through holes), it is sufficiently suppressed that the electron cloud generated outside the through holes enters the through holes. On the other hand, it is presumed that the primary electrons generated with high efficiency in the photoelectric conversion part substantially contribute to the electron / photo multiplication in the through hole. However, the mechanism of action is not limited to this.

  Further, the material of the photoelectric conversion part is not particularly limited as long as it includes a substance that interacts with an electromagnetic wave, a particle beam, or the like of a target measurement object, and as a result, generates an electromagnetic wave, a particle beam, etc. In addition to transition metals, heavy metals, and noble metals, those containing alkali metal electrons and those having a large reaction cross-section with the object to be measured are included. More specifically, for example, when the measurement target is visible light (wavelength of about 400 nm to 800 nm), a multi-alkali containing a plurality of types of alkali metals described later is preferable, particularly for visible light having a wavelength of about 300 nm to 600 nm. Bialkali is more preferable. In addition, in the case of vacuum ultraviolet light having a wavelength shorter than about 200 nm, CsI is more preferable, and Au, Cs, and the like can be exemplified as preferable metals for shorter wavelength X-rays to γ-rays. Furthermore, when the measurement object is a neutron beam, one containing B, Gd, or the like is preferable. Thus, the thing containing an alkali metal electron is especially useful as a material of a photoelectric conversion part, when a measuring object is electromagnetic waves.

  The inventor makes a prototype of an MCP provided with a photoelectric conversion unit including an alkali metal atom, and uses the reverse bias voltage described above, for example, instead of the CP of the imaging X-ray detection apparatus described in Patent Document 1. As a result of driving in the “high resolution mode”, it was confirmed that in this case as well, sufficient resolution characteristics were obtained, and the luminance equivalent to the above “high luminance mode” was achieved. In addition, the evaluation of the pulse wave height spectrum revealed the contribution of photoelectrons generated by the interaction between the alkali metal and the X-ray. From these results, the photoelectrons generated by the interaction between the X-rays and the metal atoms such as alkali metals contained in the photoelectric conversion part are strongly electron and photoproliferation electron sources (that is, primary electrons) in the through holes. It is suggested. Furthermore, in the electric field simulation by Maxwell & Garfield, even when a photoelectric conversion part containing alkali metal atoms is provided in the circumferential direction of the inner wall of the end of the through hole, an electron cloud generated outside the MCP is incident on the through hole. It was confirmed that it was difficult.

  Furthermore, in the electric field simulation by Maxwell & Garfield, the height (the length along the axial direction of the through hole) of the photoelectric conversion unit provided on the inner wall of the through hole (the circumferential direction of the inner wall of the end); When the length of the depth of penetration into the hole is varied to some extent, when the length exceeds a certain level, most of the electron cloud generated outside the MCP may not be involved in electron / photo multiplication in the through hole. confirmed.

That is, the photoelectric conversion unit has the following formula (1);
Lcp × 0.1 <La (1),
It is more preferable that the relationship represented by In the formula, Lcp represents the axial length of the through hole, and La represents the length of the photoelectric conversion unit along the axial direction of the through hole.

  Further, it is more useful that the photoelectric conversion unit also serves as an electrode for applying a predetermined voltage to both ends of the through hole. If it carries out like this, it will become easy to achieve high sensitivity in the wide wavelength range from the wavelength range of ultraviolet light to near-infrared light. In addition, the number of electrons generated at the end of the through hole can be increased with respect to electromagnetic waves having a shorter wavelength such as X-rays. Therefore, high sensitivity can be easily realized over a wide wavelength range.

  Specifically, it is more preferable that the photoelectric conversion unit includes a plurality of types of alkali metal atoms. In this way, the photoelectric conversion efficiency can be further increased. For example, in the case of X-rays, the number of electrons generated at the end of the through hole can be further increased.

  More specifically, the plurality of through-holes have an inner wall section that is substantially straight.

  The gas proportional counter according to the present invention is mainly filled with a detection gas containing an inert gas, and includes a chamber having a window for receiving electromagnetic waves or ionizing radiation, and the MCP according to the present invention disposed in the chamber. Is provided. The “proportional counter tube” is not limited to a tubular member, but means a general counting device that operates in a proportional counter region.

  Furthermore, it is preferable that the detection gas contains an organic gas containing a halogen atom in the molecule.

In the case where a mixed gas in which an amine gas such as TMA or TEA is added to the above-described gas mainly composed of Ar gas and CH ₄ gas, for example, the wavelength of 127 nm, which is excitation light of Ar, is emitted by TMA. After conversion, light having a wavelength of 290 nm is emitted. Therefore, in a normal imaging device, conversion to visible light is necessary. In contrast, the detection gas contains an organic gas containing a halogen atom in the molecule (for example, a hydrocarbon gas in which at least one hydrogen atom such as a halogenated alkane such as CF ₄ is substituted with a fluorine atom). If so, visible light having a longer wavelength than conventional ones (when CF ₄ is included, light emission region of about 400 to 900 nm, peak wavelength of about 620 nm) can be emitted with high efficiency.

  The imaging apparatus according to the present invention includes the proportional counter according to the present invention and a photodetector arranged at the rear stage of the chamber. In other words, in consideration of the circumstances so far, the MCP according to the present invention includes a substrate having a plurality of through holes and having an insulating property, and is mainly disposed in a gas atmosphere containing an inert gas. It is also possible to express that the base has a photoelectric conversion unit including an alkali metal atom provided around the opening end of the through hole, and a plurality of photoelectric conversion units are included. It is preferable that it is provided on the inner wall of the through hole.

  According to the MCP, the gas proportional counter, and the imaging device of the present invention, electrons generated outside the MCP by the photoelectric conversion unit including alkali metal atoms provided around the opening end of the through hole formed in the MCP. While the cloud is suppressed from entering the through-hole, the primary electrons generated with high efficiency in the photoelectric conversion part substantially contribute to the electron / photo multiplication in the through-hole, so that high brightness and high An excellent characteristic that both resolutions can be achieved simultaneously can be realized.

  Hereinafter, embodiments of the present invention will be described in detail. In addition, the same code | symbol is attached | subjected to the same element and the overlapping description is abbreviate | omitted. Further, the positional relationship such as up, down, left and right is based on the positional relationship shown in the drawings unless otherwise specified. Furthermore, the dimensional ratios in the drawings are not limited to the illustrated ratios.

  FIG. 1 is a plan view schematically showing a preferred embodiment of the MCP according to the present invention, and FIG. 2 is a sectional view taken along line II-II in FIG. The MCP 1 is obtained by bonding an outer peripheral frame 12 around a plate-like insulating perforated plate 11 (substrate). The perforated plate 11 is provided with a plurality of channels 13 (through holes) along its thickness direction, and the material is not particularly limited. For example, the perforated plate 11 is bonded to a glass frame described in Patent Document 1 or the like. Examples thereof include channel glass made of a capillary plate (which may or may not contain lead), a resin frame described in Patent Document 2 in which a plurality of resin hollow fiber tubes are arranged, and the like.

  These channels 13 provided in the perforated plate 11 constitute independent electron / photomultipliers. Furthermore, on both surfaces of the perforated plate 11, for example, an electrode 1a (photoelectric conversion unit) including a thin film made of a transition metal alloy (for example, Inconel) formed by vacuum deposition or the like, a metal containing an alkali metal atom, or the like, and an electrode 1b is provided.

  Examples of the metal material containing an alkali metal atom used for the electrodes 1a and 1b include bialkali compounds, multialkali compounds, bialkali and antimony or tellurium compounds, or multialkali and antimony or tellurium compounds. The electrodes 1a and 1b may further include other layers made of carbon nanotubes or the like, and may include nuclides having a large neutron absorption cross section (reaction cross section with neutrons), for example. .

  Here, FIG. 3 is an enlarged view of a main part of FIG. 2, and is a cross-sectional view schematically showing the channel 13 and its periphery. The channel 13 is formed in an elongated straight hole shape, that is, an inner wall 13a is straight, and an inner diameter thereof is substantially constant along the extending axis G. In the figure, the channel 13 has a bias angle (an angle formed between the direction perpendicular to the plane of the perforated plate 11 and the extending axis G) of approximately 0 °, but for example, a bias angle of about 5 to 15 °. You may make it become.

  The electrodes 1a and 1b are provided so as to cover the periphery of the open end of the channel 13, and so as to enter the inside from the open end of the channel 13, that is, up to the top of the inner wall 13a at the end of the channel 13. It is extended.

Further, one electrode 1a (as will be described later, MCP1 is provided on the side CP _IN electromagnetic waves incident X-rays such as when provided in the image pickup device electrodes) is preferably represented by the following formula (1);
Lcp × 0.1 <La (1),
More preferably,
Lcp × 0.2 ≦ La ≦ Lcp × 0.5 (2),
It is provided to satisfy the relationship represented by

  Here, Lcp indicates the total length of the channel 13 in the extending axis G direction (thickness of the porous plate 11), and La indicates the length of the electrode 1a along the extending axis G direction of the channel 13 (inside the channel 13). The height of the electrode 1a in FIG.

  In the MCP 1 configured as described above, when a voltage is applied between the electrodes 1 a and 1 b, that is, both ends of each channel 13, an electric field in the extending axis G direction is generated in the channel 13. At this time, when electrons (primary electrons) generated by the photoelectric effect at the electrode 1 a are incident on the channel 13 from one end, the incident electrons are given energy from the strong electric field formed in the channel 13. The ionization / excitation collisions with the gas atoms are repeated in multiple (avalanche style), and the electrons and light (excitation light emission) increase exponentially and electron / photo multiplication is performed.

  FIG. 4 is a perspective view (partially broken view) showing a preferred embodiment of an imaging apparatus using a gas proportional counter (CGPC) of the present invention provided with MCP1. FIG. 5 is a cross-sectional view schematically showing the main part.

  The imaging X-ray detection apparatus 200 (imaging apparatus) is configured by connecting an imaging system 210 to a power supply system 34 and a control system 35 (also serving as a measurement circuit system) in which a CAMCA unit and a display device are incorporated. . The imaging system 210 has a substantially cylindrical shape, the upper end of which is covered with a beryllium window 21 (window) and the side wall is provided with an exhaust port 22a and an intake port 22b, and an X-ray Pv (electromagnetic wave) incident direction. On the other hand, it has a chamber 23 joined to the rear stage of the chamber 22.

  In the chamber 22, hollow shaping rings (shaping rings) 215 and 216 and the above-described MCP 1 are coaxially provided from the upstream side along the incident direction of the X-ray Pv. These shaping rings 215 and 216 are connected to the power supply system 34 and the ground potential, so that a high voltage from the power supply system 34 and the ground are resistance-divided so that an appropriate drift voltage is applied to each. It has become. These shaping rings 215 and 216 define a drift region in the front space of MCP1.

  The electrodes 1a and 1b of the MCP 1 are connected to the power supply system 34, respectively. A predetermined cathode voltage is applied to the electrode 1a to act as an anode, and a predetermined anode voltage is applied to the electrode 1b to form a cathode. Function as.

Further, an opening is provided at the boundary between the chambers 22 and 23, and the FOP 2 is fitted and installed therein so as to seal the chamber 22 side. In the space in the chamber 22 thus closed, the main gas components such as He gas, Ar gas, Xe gas, CH ₄ gas, and the like preferably contain a halogen atom, more preferably a fluorine atom in the molecule. _An organic gas such as a halogenated alkane such as ₄ is added, and a detection gas 217 to which a quenching gas is added as necessary is enclosed. The detection gas 217 is appropriately exhausted and sucked using the exhaust port 22a and the intake port 22b.

The addition amount of an organic gas such as CF ₄ can be appropriately selected according to the type of gas, but is preferably about 1 to 10% by volume, more preferably several volume% with respect to the total amount of the detection gas 217. It is said. Thus, the proportional counter of the present invention is constituted by the beryllium window 21, the chamber 22, the shaping rings 215 and 216, the MCP 1, and the detection gas 217.

  Further, on the bottom wall of the chamber 23, an optical position detector 3 (photo detector) is installed coaxially with the MCP 1 and the FOP 2, and a drive for driving the optical position detector 3 is provided around the optical position detector 3. A circuit board 4 is provided. As the optical position detector 3, an optical detector capable of two-dimensional position detection is preferable. For example, a CMOS sensor array, an image intensifier (II), a CCD, an ICCD, a PMT, or an anode board is used. Examples include the imaging sensor used.

  Furthermore, the power supply system 34 described above is connected to the shaping rings 215 and 216 and the MCP 1 via the power supply terminal 24 provided on the side wall of the chamber 23, and is connected to the drive circuit board 4 and the optical position via the power supply terminal 24. Driving power is also supplied to the detector 3. Furthermore, the control system 35 is connected to the drive circuit board 4 via a signal terminal 25 provided on the side wall of the chamber 23.

  In the imaging X-ray detection apparatus 200 using the gas proportional counter including the MCP 1 configured as described above, the X-ray Pv incident into the chamber 22 through the beryllium window 21 is between the beryllium window 21 and the MCP 1. It interacts with gas molecules in the defined region (drift region), and high energy primary electrons (X-ray photoelectrons) are emitted by the photoelectric effect. The primary electrons travel while applying energy to other gas molecules, and generate electron-ion pairs in the tracks, thereby forming an electron cloud.

  A forward bias voltage similar to that in the conventional high brightness mode is applied to the drift region, and an electron cloud generated by primary electrons is generated by an electric field (for example, an intensity of about 100 V / cm) formed by the forward bias voltage. Move (drift) to the side. The electrons that have moved to the MCP 1 side in this way enter the channel of the MCP in the conventional device, but the MCP 1 of the present invention is prevented from entering the channel 13.

Here, the result of the electric field simulation using the Maxwell & Garfield three-dimensional simulation code performed by the present inventor in order to elucidate the behavior of such electrons will be described. The outline of the structural model near the MCP 1 used in the simulation is as follows. The shape of the channel 13 is basically the same as that shown in FIG. 3, and the following symbols are the symbols in FIG.
-Total length Lcp of channel 13: 500 μm
-Inner diameter D of channel 13: 50 μm
Distance electrode 1a and the front potential point V _top L _top: 500μm
_{-Distance Lbot} between electrode 1a and rear potential point _Vbot : 500 [ _mu] m
-Length La in the channel 13 of the electrode 1a: 25, 50, 100 μm
The length Lb in the channel 13 of the electrode 1b: 50 μm
-Upper potential point potential: + 45.8V
-Potential of electrode 1a: + 50V
-Potential of electrode 1b: + 1050V
-Potential at the lower potential point: + 1045V

In this model, the electric field strength in the drift region in front of the electrode 1a is 100 V / cm, and the electric field strength in the channel 13 is 2 × 10 ⁴ V / cm or more.

  6 to 8 are diagrams showing calculation results of contour lines (potential contour lines) distribution in the vicinity of the opening of the channel 13 when La is 25, 50, and 100 μm, respectively. It was confirmed that as the electrode length La was larger, the portion where the equiwire interval was denser changed to a deeper position inside the channel 13.

  Moreover, FIGS. 9-11 is a figure which shows the calculation result of the electric field strength in the channel 13 in La, respectively 25, 50, and 100 micrometers. When the length of the electrode 1a was changed to 25, 50, and 100 μm, it was confirmed that the electric field in the channel 13 increased to a maximum of 23, 24.5, and 28 kV / cm. Thus, when the length of the electrode 1a is increased, the electric field strength in the channel 13 is increased. Conversely, as the length of the electrode 1a is larger, the same electric field strength can be obtained at a lower voltage. It has been found.

  Further, FIGS. 12 to 14 are diagrams showing calculation results of electron movement (drift) states in the channel 13 and the vicinity thereof when La is 25, 50, and 100 μm under the condition that no gas exists in front of the electrode 1a. is there. It has been confirmed that the electrons E in front of the electrode 1a are less likely to enter the channel 13 as the length of the electrode 1a increases.

  15 to 17 are diagrams showing calculation results of electron movement (drift) states in the channel 13 and the vicinity thereof when La is 25, 50, and 100 μm, respectively, under the condition that gas exists in front of the electrode 1a. It is. Also in this case, it has been found that the electrons E in front of the electrode 1a are less likely to enter the channel 13 as the length of the electrode 1a increases.

Furthermore, 1000 virtual electrons are arranged at a distance of 400 μm from the electrode 1 a to the front potential point V _top side and at a position on the extending axis G of the channel 13, their behavior, and the gas inside the channel 13. The percentage of electrons that contributed (participated) to electron proliferation by interaction was calculated and evaluated. The results are summarized in Table 1.

  From these results, as the length of the electrode 1a becomes longer, the number of electrons stopped at the electrode 1a increases, thereby reducing the number of electrons reaching the channel 13 and further contributing to electron multiplication in the channel 13. It was confirmed that the percentage of electrons to be reduced. In particular, when the length La of the electrode 1a is larger than 50 μm (that is, La = Lcp × 0.1), the proportion of the electrons E generated in the drift region in front of the electrode 1a contributing to the electron multiplication in the channel 13 is remarkably high. It is understood that when La becomes 100 μm (ie, La = Lcp × 0.2) or more, the contribution ratio becomes substantially negligible.

  As described above, the electrons E in the drift region in front of the electrode 1a are less likely to enter the channel 13 as shown in FIGS. One of the reasons is that the electrons that are entering the open end of the channel 13 move so as to enter the electrode 1a (see FIGS. 12 to 14) by changing the part to a deeper position inside the channel 13. One is estimated. However, the action is not limited to this.

  Thus, the electron cloud generated in the drift region becomes difficult to enter the channel 13 and some of the X-rays Pv incident into the chamber 22 reach the MCP 1 without being converted into electrons due to the interaction with the gas molecules. There is. When this X-ray Pv enters the electrode 1a, photoelectric conversion is caused by the interaction with the electrode 1a, and photoelectrons can be generated. At this time, since the electrode 1a contains an alkali metal atom having a large reaction cross-sectional area for photoelectric conversion, the generation efficiency of photoelectrons is increased.

Photoelectrons generated from the electrode 1a are generated in the vicinity of the opening of the channel 13 or inside the channel 13, and therefore enter the channel 13 immediately. An electric field of, for example, 10 ⁴ V / cm or more sufficient to cause gas discharge and excitation light emission is formed inside the channel 13 by the voltage applied to the electrodes 1a and 1b. Collisions occur one after another, and electron multiplication and photo multiplication are performed.

At this time, various elementary reactions are caused, and in particular, when the excited CF ₄ molecule transitions to the ground state, light having a wavelength peculiar to the energy transition is emitted (CF ₄ ^* → CF ₄ + hν). . The wavelength region of the excitation light emission is a wide one (about 400 to 900 nm) from visible light to infrared light region, and its peak wavelength is about 620 nm. This emission wavelength tends to best match the sensitivity of the CCD among the specific devices of the optical position detector 3 described above.

  The light thus propagated passes through the FOP 2 and enters the optical position detector 3 without being photoelectrically converted again. From the optical position detector 3, an electrical signal based on the two-dimensional position information on which light is incident and the light intensity at each incident position is output to the control system 35 through the drive circuit board 4, where a three-dimensional X-ray emission image is generated. It is comprised and output to a display apparatus etc.

20 to 22, MCP1 using Inconel 600 (Inconel 600) as the electrodes 1a and 1b is manufactured with the inner diameter D of the channel 13 being 100 μm, and the test pattern (aperture) shown in FIG. 19 is beryllium. It is a photograph which shows the result of having imaged, irradiating X-ray | X_line in the high resolution mode which mounts in front of the window 21 and applies a reverse bias voltage. The chamber 23 was filled with an Ar + CF ₄ mixed gas having a predetermined pressure. 20 to 22 show the results when the pressure of the mixed gas is 1 atmosphere, 0.5 atmosphere, and 0.25 atmosphere, respectively. Moreover, the larger the numerical value displayed in FIG. 20 to FIG. 22, the denser the straight line projected next to it.

  From these results, it was confirmed that the imaging X-ray detection apparatus 200 using the MCP 1 according to the present invention and the gas proportional counter equipped with the MCP 1 has sufficient imaging sensitivity even in a high resolution mode with extremely excellent position resolution. It was. In addition, in the operation in the high brightness mode in which the forward bias is applied, since the track length of the electrons usually increases as the gas pressure in the chamber decreases, the resolution tends to deteriorate as the gas pressure decreases. As apparent from FIGS. 20 to 22, in the imaging X-ray detection apparatus 200 using the MCP 1 and the gas proportional counter equipped with the MCP 1 according to the present invention, the resolution can be improved even if the gas pressure in the chamber changes. It was found that no deterioration was observed.

  According to the imaging X-ray detection apparatus 200 using the gas proportional counter including the MCP 1 configured as described above, electrons generated with high efficiency due to the interaction between the alkali metal atom contained in the electrode 1a and the X-ray Pv. However, since it becomes an electron source for electron and photoreproduction within the channel 13, imaging with high luminance (high sensitivity) becomes possible. In addition, the electron cloud generated in the drift region moves to the MCP 1 side while being diffused in the gas. However, they are prevented from entering the MCP 1 and the photoelectrons generated in the vicinity of the channel 13 and in the inside thereof are Since there is almost no diffusion in the gas, the information of the position where the X-ray Pv is incident is held more accurately. Since these photoelectrons serve as the electron source for photoelectron multiplication in the channel 13, excellent position resolution determined by the inner diameter of the channel 13 can be realized. In this way, X-ray imaging with high brightness and high resolution is realized.

  In addition, this invention is not limited to each embodiment mentioned above, A various deformation | transformation is possible in the range which does not deviate from the summary. For example, the shape of the MCP 1 is not limited to a disc shape, and may be a square plate shape, for example. FIG. 18 is a perspective view schematically showing another example of such an MCP of the present invention. The MCP 10 includes a rectangular outer peripheral frame 212, and a base body 211 made of an insulating member such as glass or resin and provided with a large number of channels 13 is provided inside the MCP 10. Further, the MCPs 1 and 10 may not have the outer peripheral frames 12 and 212.

Still further, the gas for detection 217 may be added with a gas exhibiting other Penning effects such as TMA and TEA instead of or in addition to the CF ₄ gas, but the excitation light wavelength is in the visible region as described above. Therefore, an organic gas such as a halogenated alkane such as CF ₄ is more preferable. Furthermore, a combination of a conventional light transmission window and an optical system may be used instead of FOP2, or a bundle-shaped optical fiber may be used. In addition, the electrode 1b may not contain alkali metal atoms.

  In the above-described embodiment, the detection and imaging of X-rays have been described. However, the detection target is not limited to X-rays, and the MCN, the gas proportional counter, and the imaging device according to the present invention may include other electromagnetic waves and ionizing radiation. It can be used for detection. In particular, since the photoelectric conversion portion contains an alkali metal atom, it has high sensitivity to light having a wavelength from the ultraviolet region to the near infrared region, and in that case, the above-described excellent position resolution can be realized.

Furthermore, the electrode 1a may be provided with a layer containing a nuclide (for example, ¹⁰ B) having a large neutron absorption cross section (reaction cross section with neutrons). In this case, it also functions as a neutron detection device. To do. That is, in this case, in the electrode 1a, the following formula (3);
¹⁰ B + n → ⁴ He + ⁷ Li + 2.78 MeV (3)
A nuclear reaction represented by The ⁴ He (α-ray) and ⁷ Li released at this time give energy to the gas in the channel 13 to generate a primary electron cloud, and this primary electron cloud becomes a source of electron / photo multiplication in the channel 13. obtain. Thereby, position resolution of the order of μm can be achieved in neutron detection. Since the position resolution of a normal neutron detector using gas is in the order of centimeters, according to the MCN, gas proportional counter, and imaging device of the present invention, the position resolution in neutron detection is about 1000 times that of the prior art. It becomes possible to improve.

  Furthermore, the material of the perforated plate 11 is not particularly limited, but if glass is used, the reaction between alkali metal atoms and oxygen contained in the electrode 1a can be suppressed, which is preferable from the viewpoint of preventing deterioration of the electrode 1a with time.

  As described above, according to the microchannel plate, the gas proportional counter, and the imaging device of the present invention, both high luminance and high resolution can be achieved at the same time. Therefore, various electromagnetic waves or ionizing radiation including position detection can be achieved. It can be widely used for measurement.

1 is a plan view schematically showing a preferred embodiment of an MCP according to the present invention. It is the II-II sectional view taken on the line in FIG. FIG. 3 is an enlarged view of a main part of FIG. 2, and is a cross-sectional view schematically showing a channel 13 and its periphery. It is a perspective view which shows suitable one Embodiment of the imaging device using the gas proportional counter of this invention provided with MCP1. It is sectional drawing which shows typically the principal part of the imaging device shown in FIG. It is a figure which shows the calculation result of the equal electric wire distribution in the opening part vicinity of the channel 13 when length La of the electrode 1a is 25 micrometers. It is a figure which shows the calculation result of the equal electric wire distribution in the opening part vicinity of the channel 13 when length La of the electrode 1a is 50 micrometers. It is a figure which shows the calculation result of the equal electric wire distribution in the opening part vicinity of the channel 13 when length La of the electrode 1a is 100 micrometers. It is a figure which shows the calculation result of the electric field strength in the channel 13 when length La of the electrode 1a is 25 micrometers. It is a figure which shows the calculation result of the electric field strength in the channel 13 in case the length La of the electrode 1a is 50 micrometers. It is a figure which shows the calculation result of the electric field strength in the channel 13 when length La of the electrode 1a is 100 micrometers. It is a figure which shows the calculation result of the movement state of the electron in the channel 13 and the vicinity in case the length La of the electrode 1a is 25 micrometers on condition that the gas does not exist ahead of the electrode 1a. It is a figure which shows the calculation result of the movement state of the electron in the channel 13 and the vicinity in case the length La of the electrode 1a is 50 micrometers in the conditions where gas does not exist ahead of the electrode 1a. It is a figure which shows the calculation result of the movement state of the electron in the channel 13 and its vicinity in case the length La of the electrode 1a is 100 micrometers on condition that the gas does not exist ahead of the electrode 1a. It is a figure which shows the calculation result of the movement state of the electron in the channel 13 and the vicinity in case the length La of the electrode 1a is 25 micrometers on the conditions that gas exists ahead of the electrode 1a. It is a figure which shows the calculation result of the movement state of the electron in the channel 13 and its vicinity in the length La of the electrode 1a on condition that the gas exists ahead of the electrode 1a. It is a figure which shows the calculation result of the movement state of the electron in the channel 13 and the vicinity in case the length La of the electrode 1a is 100 micrometers on the conditions that gas exists ahead of the electrode 1a. It is a perspective view which shows typically another example of MCP of this invention. It is a plane photograph which shows a test pattern. It is a photograph which shows the result of having drive | operated MCP1 in high-resolution mode and having imaged the test pattern by the X-ray. It is a photograph which shows the result of having drive | operated MCP1 in high-resolution mode and having imaged the test pattern by the X-ray. It is a photograph which shows the result of having drive | operated MCP1 in high-resolution mode and having imaged the test pattern by the X-ray.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,10 ... MCP, 1a ... Electrode (photoelectric conversion part), 1b ... Electrode, 3 ... Optical position detector, 4 ... Drive circuit board, 11 ... Perforated plate (base | substrate), 12, 212 ... Outer frame, 13 ... Channel (Through hole), 13a ... inner wall, 21 ... beryllium window, 22, 23 ... chamber, 22b ... intake port, 22a ... exhaust port, 24 ... power supply terminal, 25 ... signal terminal, 34 ... power supply system, 35 ... control system, DESCRIPTION OF SYMBOLS 200 ... Imaging type X-ray detection apparatus (imaging apparatus), 210 ... Imaging system, 211 ... Base | substrate, 215, 216 ... Shaping ring, 217 ... Detection gas, D ... Inner diameter, E ... Electron, G ... Extension axis, Pv ... X-ray.

Claims (7)

A plurality of through-holes and an insulating base;
The plurality of through-holes have an inner wall cross section that is substantially straight, and is perpendicular to the planar direction of the base body,
The base has a pair of electrodes for applying a predetermined voltage to both ends of the plurality of through holes,
The pair of electrodes are provided separately on the inner walls of both end portions of the plurality of through holes,
At least one of the pair of electrodes functions as a photoelectric conversion unit.
Microchannel plate. The photoelectric conversion part includes an alkali metal atom.
The microchannel plate according to claim 1. The photoelectric conversion unit has the following formula (1);
Lcp × 0.1 <La (1),
Lcp: axial length of the through hole,
La: The length of the photoelectric conversion unit along the axial direction of the through hole,
Satisfying the relationship represented by
The microchannel plate according to claim 2. The photoelectric conversion part includes a plurality of types of alkali metal atoms.
The microchannel plate according to any one of claims 1 to 3 . A chamber which is filled with a detection gas containing mainly an inert gas and has a window for receiving electromagnetic waves or ionizing radiation;
The microchannel plate according to any one of claims 1 to 4 , which is disposed in the chamber;
Gas proportional counter with. The detection gas contains an organic gas containing a halogen atom in the molecule.
The gas proportional counter according to claim 5 . A gas proportional counter according to claim 5 or 6 ,
A photodetector disposed downstream of the chamber;
An imaging apparatus comprising: