JPH0963533A - Electron multiplier device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electron multiplier device improved in space resolution, SOLUTION: This electron multiplier device includes a microchannel plate 1, and the microchannel plate 1 includes at least one channel 2 for multiplying secondary electrons (e) on receiving an energy ray R. The channel 2 has a cross-sectional diameter D ranging from 3 to 5μm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron multiplying device capable of observing signals by energy rays such as X-rays with high efficiency, and more particularly to improving the spatial resolution of an electron multiplying device including a channel plate. .

[0002]

2. Description of the Related Art Conventionally, an electron multiplying device including a microchannel plate (MCP) has been used to detect a signal due to energy rays and to visualize the signal in two dimensions. Here, energy rays represent a broad concept including charged particles such as electrons and ions, neutral particles, and various lights including X-rays and γ-rays.

Generally, the MCP includes a large number of channels penetrating in the thickness direction thereof, and these channels cause a large number of secondary electrons to be proliferated by being excited by the irradiated energy rays. Then, by converting these propagated secondary electron signals into a two-dimensional image, the weak information contained in the original energy ray can be read.

[0004]

In the conventional electron multiplier including the MCP, an ordinary electron multiplier having a channel diameter of 12 μm and having about 50 μm on a two-dimensional image is used.
Only a spatial resolution of μm is obtained, and even with a small channel diameter of 6 μm, only a resolution of about 30 μm is obtained.

Therefore, an object of the present invention is to provide an electron multiplying device which can obtain an improved spatial resolution.

[0006]

An electron multiplier according to one aspect of the present invention includes a microchannel plate,
The microchannel plate includes at least one channel for receiving energy rays and propagating secondary electrons, the channel being characterized by having a cross-sectional diameter in the range of 3-5 μm.

An electron multiplying device according to another aspect of the present invention includes a microchannel plate, the microchannel plate having a first electrode formed on a first surface for receiving the energy beam and the energy beam. Receive 2
At least one channel for propagating secondary electrons and a second electrode formed on a second surface that emits propagated secondary electrons, the second electrode extending into the channel The length that is present is characterized by having a length that exceeds 2.5 times the cross-sectional diameter of the channel and that can be inserted into the channel by vapor deposition.

An electron multiplying device according to yet another aspect of the present invention includes a microchannel plate, the microchannel plate having a first electrode formed on a first surface for receiving an energy beam and an energy beam. The electron multiplying device further includes at least one channel for receiving and multiplying secondary electrons, and a second electrode formed on the second surface for emitting the multiplied secondary electrons. The phosphor layer is disposed to face the second electrode and converts the energy of secondary electrons emitted from the channel plate into visible light. The phosphor layer has a thickness of 15 μm.
It is characterized by having a thickness of m or less.

[0009]

1 is a schematic sectional view showing an example of an embodiment of an electron multiplying device according to the present invention. In this cross-sectional view, the dimensional relationship of each portion does not necessarily represent an actual dimensional relationship for the sake of clarity of the drawing.

The electron multiplier of FIG. 1 includes a microchannel plate (MCP) 1. Normally, the MCP contains many microchannels, but the MC of FIG.
In P1, only one channel 2 is shown magnified typically. The input side electrode 3 is formed on the input side surface of the MCP 1 which receives the energy rays R. On the other hand, the output side electrode 4 is formed on the output side surface of the MCP 1 from which secondary electrons are emitted.

An optical fiber plate 5 facing the output electrode 4 and having a large number of optical fibers bundled in the thickness direction.
The phosphor layer 6 formed above is arranged. An accelerating electrode 7 for accelerating the secondary electrons emitted from the MCP 1 toward the phosphor layer 6 is formed on the phosphor layer 6. The acceleration electrode 7 can usually be formed of Al.

In the electron multiplier as shown in FIG. 1, when the energy ray R enters the channel 2, the energy ray R collides with the inner wall of the channel 2 and a large number of secondary electrons e are generated from the collision point. Is released. These secondary electrons e collide with the opposite walls in the channel 2 again while being accelerated toward the output side by the voltage E1 applied between the input side electrode 3 and the output side electrode 4, and again a large number of secondary electrons e are generated. Emit the electron e. As a result of the secondary electron emission process being repeated many times along the channel 2, a large number of secondary electrons e are emitted from the output side.

The secondary electrons e emitted from the output side of the MCP1 are accelerated toward the phosphor layer 6 by the voltage E2 applied between the output side electrode 4 of the MCP1 and the acceleration electrode 7,
The electron energy is converted into visible light VL and emitted. These visible lights VL are taken into the optical fiber plate 5 and can be observed as a two-dimensional image on the lower surface of the optical fiber plate 5.

In an electron multiplier as shown in FIG. 1, the cross-sectional diameter D of the channel 2 is conventionally 12
μm, and even the smallest is 6 μm. However, the channel 2 of the PCM 1 in the electron multiplier according to the invention has a cross-sectional diameter D of 3 μm to 5 μm. Therefore, for example, by decreasing the channel diameter D from the conventional minimum value of 6 μm to 4 μm within the range of the present invention, the lateral spread of the secondary electrons on the output surface of the MCP is reduced from 6 μm to 4 μm. You can This contributes to increase the resolution of the image on the lower surface of the optical fiber plate 5. However, if the channel diameter D is smaller than 3 μm, the electron density in the channel 2 becomes too large and the electron gain is saturated. Therefore, as a result of the calculation, the preferable range of the channel diameter D is 3 to 5 μm. It was found to be in the range.

Referring to FIG. 2, the output side of channel 2 is shown enlarged. The input side electrode 3 and the output side electrode 4 are formed on the input surface and the output surface of the MCP 1 by depositing Inconel or Ni—Cr. These electrodes are vapor-deposited so as to evenly enter the inside of the channel 2, and the depth L thereof is set to a constant value within the range of 0.5 times to 2.5 times the channel diameter D. Usually, L = D is often set.

FIG. 2 (A) shows the output side electrode 4 in the conventional MCP 1, and FIG. 2 (B) shows the output side electrode 4 in the MCP 1 according to the present invention. That is, the conventional output side electrode 4 in FIG. 2A extends into the channel 2 up to a length L which is, for example, about 0.5 times the channel diameter D, whereas in FIG. 2B. The output electrode 4 in the present invention extends into the channel 2 to a length L which is, for example, about three times the channel diameter D. At this time, the electrons colliding with the portion of the output side electrode 4 extending into the channel 2 are not absorbed by the electrode 4 and do not emit secondary electrons. Therefore, FIG.
As shown in (A), when the length L of the output-side electrode 4 in the channel 2 is short, the divergence angle θ of the secondary electron emitted from the output hole of the channel 2 becomes large. On the other hand, as shown in FIG. 2 (B), when the length L of the output side electrode 4 in the channel 2 is large, the electron e colliding with the electrode 4 is absorbed and a secondary electron is generated. , The collimation of the electron flow emitted from channel 2 can be increased, and the divergence angle θ is
It is smaller than in the case of (A).

The electron flow having a small divergence angle θ contributes to increase the resolution of the two-dimensional image on the lower surface of the optical fiber plate 5 in FIG. Therefore, in the electron multiplying device of the present invention, the length L of the output electrode 4 extending into the channel 2 is set to be 3 times or more the channel diameter D. However, since the electrode 4 is formed by vapor deposition, the length L of the electrode 4 in the channel 2 is limited. That is, in the present invention, the length L of the output-side electrode 4 in the channel 2 is set to be not less than 3 times the channel diameter D and within the range that can be formed by vapor deposition.

Referring again to FIG. 1, the distance between the output side electrode 4 and the acceleration electrode 7 is usually about 1 mm. And conventionally, between the output side electrode 4 and the acceleration electrode 7, normally 5
A voltage of kV is applied. However, in the present invention, a voltage of 6 to 10 kV is applied between the output side electrode 4 and the acceleration electrode 7. That is, in the electron multiplying device according to the present invention, the acceleration voltage between the MCP 1 and the accelerating electrode 7 is large, so that the time required for the electrons e emitted from the MCP 1 to reach the phosphor layer 6 is shortened. At this time, the electron e has a lateral velocity component at the exit of the channel, but the lateral movement amount of the electron e is proportional to the time until the electron e reaches the phosphor layer 6. Therefore, MC
When the voltage E2 between P1 and the accelerating electrode 7 is large, the electrons e reach the phosphor layer 6 without spreading in the lateral direction, so that the large accelerating voltage E2 is different from the resolution of the image on the lower surface of the optical fiber plate 5. It will contribute to improvement. In the present invention, the maximum value of the acceleration voltage E2 is limited to 10 kV, because if the acceleration voltage E2 is further increased, discharge will occur between the output side electrode 4 and the acceleration electrode 7.

In FIG. 3, the phosphor layer 6 in the conventional electron multiplying device and a part of the phosphor layer 6 in the electron multiplying device according to the present invention are shown enlarged. The conventional phosphor layer 6 shown in FIG. 3 (A) has a thickness T of about 20 μm. On the other hand, the phosphor layer 6 in the present invention shown in FIG. 3B has a thickness T of 15 μm or less. The electrons e accelerated by the acceleration electrode 7 enter the phosphor layer 6, and the electron energy thereof is converted into visible light VL. Those visible lights VL are taken into the optical fiber plate 5 and form a two-dimensional image on the bottom surface of the optical fiber plate 5.

At this time, when the thickness T of the phosphor layer 6 is large, as shown in FIG. 3A, the range of light generation points that can be taken into one optical fiber is a large width W. Will have. On the other hand, when the thickness T of the phosphor layer 6 is small, as shown in FIG. 3B, the width W including the generation point of light that can be taken into one optical fiber becomes small.
This small width W acts to increase the resolution of the image formed on the lower surface of the optical fiber plate 5.

[0021]

EXAMPLE As an example of the implementation of the present invention, an electron multiplying device was manufactured and the spatial resolution of the lower surface of the optical fiber plate 5 was measured.

As the energy ray R, an ArF excimer laser having a wavelength of about 193 nm was used. PCM
Each of the multiple channels 2 contained in 1 had a diameter D of 4 μm and the output electrode 4 had a length L of 12 μm in the channel 2. In addition, the output side electrode 4 and the acceleration electrode 7
10 KV was applied as an accelerating voltage between and. Furthermore, the phosphor layer 6 had a thickness of 10 μm, and each fiber included in the optical fiber plate 5 had a cross-sectional diameter of 3 μm. In order to measure the spatial resolution, a line-and-space striped mesh made of a thin film of Au having a thickness of 3 μm is arranged at a position separated by 1 mm from the input surface of the MCP1, and the striped mesh is formed. The spatial frequency transmittance was measured by sequentially changing the thickness of the.

FIG. 4 schematically illustrates the principle of measuring the transmittance of this spatial frequency. In FIG. 4, the light intensity observed on the lower surface of the optical fiber plate 5 is shown corresponding to the line and space 8 formed of the Au thin film. That is, the horizontal axis of the graph in FIG. 4 represents the spatial position, and the vertical axis represents the light intensity as a relative value.
When the resolution of the electron multiplier is ideal, the observed light intensity should have a distribution as shown by the rectangular wave 4A. However, the actually observed light intensity distribution becomes a curve 4B similar to a trigonometric function. Here, as a numerical value representing the spatial resolution, MTF (Modulation Transfer Functio
The general index n) is used. MTF is curve 4B
If the value of the mountain is a and the value of the valley is b, MTF = (a
−b) × 100 / (a + b) (%)

FIG. 5 shows the measurement result of the transmittance of this spatial frequency. In the graph of FIG. 5, the horizontal axis represents the spatial frequency (the number of line / space pairs / mm), and the vertical axis represents the MTF (%).

FIG. 6 shows the light intensity distribution obtained from the result of FIG. That is, the horizontal axis in FIG. 6 represents the spatial position (μm), and the vertical axis represents the light intensity (relative value). In FIG. 6, the half width of the light intensity is 10 μm. From this result, in the electron multiplier according to the present invention, the spatial spread (spatial resolution) of the bright spot on the lower surface of the optical fiber plate 5 is 10 μm when the bright spot having the area of 0 enters the MCP 1. Recognize. That is, in this embodiment, it is understood that the conventional best spatial resolution is improved from about 30 μm to 10 μm.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing an example of an electron multiplying device according to the present invention.

FIG. 2 is a diagram showing a relationship between a length of an output side electrode in a channel and a divergence angle of emitted secondary electrons.

FIG. 3 is a cross-sectional view showing the relationship between the thickness of a phosphor layer and the range of light emitting points incorporated in an optical fiber plate.

FIG. 4 is a graph for explaining an evaluation method of spatial resolution.

FIG. 5 is a graph showing a measurement result of a spatial resolution evaluation method.

FIG. 6 is a graph showing a light intensity distribution based on a measurement result of spatial resolution.

[Explanation of symbols]

 1 Micro Channel Plate 2 Channel 3 Input Side Electrode 4 Output Side Electrode 5 Optical Fiber Plate 6 Phosphor Layer 7 Accelerating Electrode R Energy Ray e Secondary Electron VL Visible Light

Claims (8)

[Claims] 1. An electron multiplying device including a microchannel plate, wherein the microchannel plate includes at least one channel for receiving an energy beam and multiplying secondary electrons, and the channel has three to three channels.
An electron multiplier having a cross-sectional diameter in the range of 5 μm. 2. An electron multiplying device including a microchannel plate, wherein the microchannel plate has a first surface formed on a first surface for receiving energy rays.
An electrode, at least one channel for receiving the energy rays to multiply secondary electrons, and a second electrode formed on the second surface for emitting the multiplied secondary electrons. , The length of the second electrode extending into the channel is 2.5 times the cross-sectional diameter of the channel.
An electron multiplying device having a length that is set to a value that exceeds double and that can be inserted into the channel by vapor deposition. 3. An electron multiplying device including a microchannel plate, wherein the microchannel plate has a first surface formed on a first surface for receiving energy rays.
An electrode, at least one channel for receiving the energy rays to multiply secondary electrons, and a second electrode formed on the second surface for emitting the multiplied secondary electrons. The electron multiplying device further includes a phosphor layer disposed facing the second electrode to convert energy of the secondary electrons emitted from the channel plate into visible light. The phosphor layer is 15 μm
An electron multiplier having the following thickness. 4. The second electrode further includes a third electrode provided on the phosphor layer so as to face the second electrode.
The voltage in the range of 6 to 10 kV is applied between the electrode and the third electrode to accelerate the secondary electrons toward the phosphor layer. Electronic multiplier. 5. The electron multiplying device according to claim 3, wherein the phosphor layer is formed on an optical fiber plate in which a large number of optical fibers are assembled along the thickness direction. . 6. The electron multiplying device according to claim 3, wherein the channel has a cross-sectional diameter in the range of 3 to 5 μm. 7. The electron multiplying device according to claim 2, wherein the channel has a cross-sectional diameter in the range of 3 to 5 μm. 8. The length of extension of the second electrode into the channel is set to be more than 2.5 times the cross-sectional diameter of the channel and to a length such that the second electrode can be inserted into the channel by vapor deposition. 7. The electron multiplying device according to claim 3, wherein the electron multiplying device has a specified length.