JP2004354356A - Laser plasma x-ray microscope - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To supply a sufficient current onto a photoelectric transfer face and to restrain a voltage drop to observe a living organism under a living condition, when irradiated with a nano-second order of very strong short pulse X-ray. <P>SOLUTION: A charge for replenishing a photoelectron emitted from a photoelectric transfer membrane 4 is supplied by connecting an electric circuit such as a capacitor 7 to a photoelectric transfer plate 1, and by moderating the voltage drop in the photoelectric transfer plate 1, so as to provide an electron image reflected accurately with an X-ray transmission image. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a laser that converts an X-ray image formed by irradiating a short-pulse high-power laser plasma X-ray into an electronic image by a photoelectric conversion surface, enlarges the image electronically, forms an image, and observes the image via an image sensor. The present invention relates to a plasma X-ray microscope.
[0002]
[Prior art]
An X-ray microscope that optically magnifies the X-ray itself is limited in magnification of the X-ray optical element. In addition, since it is difficult to change the magnification in the X-ray optical system, it is difficult to provide a zooming function, and the operation for searching for a specific position in the sample is complicated and time-consuming. Furthermore, since it is necessary to irradiate strong X-rays, it is difficult to observe the living body alive.
[0003]
Therefore, an X-ray microscope has been developed in which an X-ray transmission image is converted into an electronic image regardless of the magnification of the X-ray itself, and can be enlarged and observed by an electron lens system.
Patent Document 1 and Japanese Patent Application No. 2002-152136 disclosed by the present applicant convert an X-ray image into an electronic image using photoelectric conversion and enlarge the electronic image as shown in FIGS. An X-ray microscope is described in which an image is formed on an image sensor and visualized for observation. The disclosed invention projects an X-ray transmission image generated by irradiating a sample with X-rays on a photoelectric conversion surface, converts the X-ray transmission image into an electronic image on the photoelectric conversion surface, and enlarges the image with an electromagnetic lens system. An image is formed on an electron beam visualization surface composed of a microchannel plate MCP or the like, and an X-ray image of the sample is observed via a CCD camera or the like.
[0004]
Since the disclosed X-ray microscope has a greatly increased magnification, the X-ray transmission image of the object can be accurately observed in detail.
Since the X-ray microscope has a zooming function, it is convenient for observing each part of the biological sample. When pulsed soft X-rays generated by a laser plasma X-ray source are used, the soft X-rays cause less damage to a biological sample than an electron beam and can be observed without staining, so that the biological sample can be observed. It is convenient.
[0005]
However, when observing a normal object using synchrotron radiation X-rays or X-ray tube-generated X-rays, there was no problem. However, when laser plasma X-rays are used, care must be taken. is there.
Laser plasma X-rays are usually obtained from plasma generated by converging a Nd: YAG laser having a pulse width of several nanoseconds, a wavelength of 1064 nm, and a repetition rate of about 10 Hz on a metal target with an optical lens. When gold Au or molybdenum Mo is used as the target material, a large amount of soft X-rays of 2 to 5 nm are generated, and pulse X-rays of several nanoseconds are obtained.
[0006]
The conversion time in the photoelectric conversion film is very short, ie, less than picoseconds, and the time for secondary electrons to be emitted from the photoelectric conversion film is almost the same. Therefore, it is possible to obtain a photoelectron image of the same type as the generated pulse X-ray. it can.
However, the disclosed photoelectric conversion type X-ray microscope manufactures the photoelectric conversion film in a thin film in order to faithfully reproduce the shape when converting the X-ray image projected on the back surface of the photoelectric conversion film into an electron image on the surface. Therefore, once the photoelectrons have been completely emitted, the next photoelectron image cannot be formed immediately because an electron deficiency state occurs unless a suitable time elapses or the electrons are replenished from the outside.
[0007]
Since laser plasma X-rays are high intensity and very short pulse X-rays, for example, about 1 × 10 ¹¹ X-rays / mm ² required to form one image are irradiated with a pulse width of 5 nanoseconds. Assuming that the conversion efficiency of a photoelectric conversion film formed of 1 mm ² of cesium iodide is 0.3 electrons per X-ray, the instantaneous photoelectron current is about It becomes very large at 1A.
Also, a protection of about 2 MΩ between the power supply device and the photoelectric conversion film so that an excessive current flowing at the time of discharging between the photoelectric conversion film and the anode does not cause damage to the power supply device, the photoelectric conversion film, the anode, and the like, and a problem of noise generation. The maximum current value is suppressed by interposing a resistor.
[0008]
However, this protection resistor has the effect of delaying the current supply from the power supply device, and cannot supply electrons to the photoelectric conversion film in a short time of nanoseconds, so that it cannot respond to irradiation with strong short pulse X-rays. Cause problems.
In addition, since a voltage drop occurs due to the photoelectron flow flowing through the protection resistor, there is a problem that the distribution of photoelectron energy is generated and an unclear image is formed.
FIG. 8 is a simulation result when the conventional circuit is irradiated with X-rays. If a current of 1 A is generated when 20 kV is applied between the photoelectric conversion film and the anode, the voltage drop of the photoelectric conversion film is reduced to about 13 kV. It has been shown that Note that the simulation was performed assuming that the high-voltage power supply and the photoelectric conversion film were connected by a high-voltage cable that could be expressed.
[0009]
The resolution δ of the X-ray microscope is affected by various aberrations, and the voltage drop ΔV between the photoelectric conversion film and the anode is
δ = C (ΔV / V) α
Is a factor of chromatic aberration according to the formula: Here, C is a chromatic aberration coefficient determined according to the lens structure, V is an applied voltage, and α is a radiation angle of the electron current.
Therefore, assuming that C = 5.43 mm and α = 0.02 rad, if a voltage drop of 13 kV occurs while applying a voltage of 20 kV, the chromatic aberration becomes about 65 μm, and the target resolution of 50 nm or less is 1000 times. Run short.
[0010]
[Patent Document 1]
JP 2003-43200 A
[Problems to be solved by the invention]
Therefore, the problem to be solved by the present invention is to supply a sufficient current to the photoelectric conversion surface and suppress a voltage drop even when irradiating a very strong short-pulse X-ray on the order of nanoseconds, thereby achieving a living state. The object of the present invention is to provide a laser plasma X-ray microscope capable of observing a living body with a microscope.
[0012]
[Means for Solving the Problems]
In order to solve the above problems, a laser plasma X-ray microscope according to the present invention is characterized in that an electric circuit for supplying a charge for supplementing photoelectrons emitted from the photoelectric conversion film is provided immediately near the photoelectric conversion film.
Since the charge supply circuit is provided immediately adjacent to the photoelectric conversion film, secondary electrons are generated by receiving strong X-rays, and charges are immediately supplied to the photoelectric conversion film in an electron-deficient state. An electron beam can be generated immediately in response to the next X-ray irradiation, as compared with the case where electrons are supplied via the device, and the movement of the object can be accurately observed.
[0013]
Note that the charge supply circuit may be formed using a capacitor. Further, the capacitance element may be a photoelectric conversion film and an anode of the electron optical system, or a capacitor element interposed between the photoelectric conversion film and the ground terminal.
Further, the capacitor element has a photoelectric conversion plate provided with a photoelectric conversion film as one electrode plate, a dielectric material is provided in close contact with the photoelectric conversion plate, and the other electrode is provided on the opposite side of the photoelectric conversion plate with the dielectric material interposed therebetween. It may be constituted by providing a plate.
The other electrode plate can also serve as the anode plate.
[0014]
By providing such a capacitive element in the photoelectric conversion film, the emitted electrons can be immediately replenished so as not to be in an electron deficiency state. Photoelectrons corresponding to the line image can be continuously emitted.
It should be noted that a coaxial cable can be connected to the photoelectric conversion surface and used as a capacitive element.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
A laser plasma X-ray microscope of the present invention will be described based on an embodiment.
FIG. 1 is a partial configuration diagram showing one embodiment of the present invention. The present embodiment uses a photoelectric conversion type X-ray microscope as shown in FIG. 7 in which an X-ray transmission image is converted into an electronic image by using a photoelectric conversion plate and can be enlarged and observed by an electron lens system. A feature is that a capacitive element is attached to the photoelectric conversion plate.
[0016]
As shown in FIG. 1, a photoelectric conversion plate 1 and an anode 2 are disposed to face each other. The photoelectric conversion plate 1 is provided with a sample holder for closely setting the sample 3 on a surface on which X-rays are incident, and a photoelectric conversion film 4 for emitting secondary electrons when X-rays enter on the back side of the X-ray incidence surface. ing.
When the photoelectric conversion plate 1 on which the sample 3 is set is irradiated with X-rays, an X-ray transmission image of the sample 3 is formed on the surface of the photoelectric conversion plate 1, and secondary electrons are generated in the photoelectric conversion film 4 correspondingly. An electron image having the same shape as the X-ray transmission image is formed.
[0017]
Here, when an accelerating voltage of 0 to -20 kV is applied between the photoelectric conversion plate 1 and the anode 2 by the accelerating power supply 4, the secondary electrons emitted following the electron image are accelerated according to the voltage, and the objective lens Then, the light is incident on an electromagnetic coil system forming a projection lens, the image is enlarged, and an image is formed on an electron beam visualization surface.
A protection resistor 6 is interposed between the acceleration power supply 5 and the photoelectric conversion plate 1 to protect the power supply device and the photoelectric conversion film and suppress noise.
[0018]
In the present embodiment, a capacitor 7 is further connected between the photoelectric conversion plate 1 and the ground terminal to accumulate charges near the photoelectric conversion film 4 so that high-intensity short pulse X-rays such as laser plasma X-rays can be generated. Even at the time of incidence, electrons can be quickly replenished so that the photoelectric conversion film 4 does not suffer from an electron deficiency state.
[0019]
FIG. 2 is a diagram showing the effect of the capacitor.
Graph (1) in FIG. 2 is the waveform of the YAG laser incident on the X-ray generator, graph (2) is the waveform of the X-ray generated by the X-ray generator, and graph (3) is the photoelectric conversion film before attaching the capacitor. 5 is a waveform of a photoelectron flow generated when the X-rays of graph (2) are incident. It can be seen that the saturation phenomenon occurs with respect to strong X-rays due to the lack of electrons in the photoelectric conversion film, which makes it impossible to accurately follow.
[0020]
In the figure, a graph (4) shows a waveform of a photoelectron flow when the X-rays of the graph (2) are incident on the photoelectric conversion plate 1 on which a capacitor is mounted. Since the electrons consumed by the photoelectric conversion are immediately compensated for, it can be seen that an electron flow that accurately reproduces the waveform up to the X-ray peak can be obtained.
[0021]
FIG. 3 is a diagram illustrating that the voltage drop in the photoelectric conversion film 4 changes according to the capacitance of the capacitor 7. FIG. 3 was created based on the result of a simulation in which the beam pulse current was 1 A in the equivalent circuit of FIG. 4 is a circuit for supplying an acceleration voltage from a power supply 5 of 20 kV via a coaxial cable 8 and a protective resistor 6 of 2 MΩ. It is further assumed that the photoelectric conversion plate 1 has a parallel capacitance 9 of 0.3 pF. A capacitor is connected in parallel with the photoelectric conversion plate 1.
[0022]
The voltage drop is 40 V when the capacitor is 100 pF, 10 V when the capacitor is 400 pF, and 5 V when the capacitor is 800 pF.
When applied to the expression of the resolution δ of the X-ray microscope, it can be seen that ΔV / V should be 0.05% and the capacitance of the capacitor should be 400 pF or more in order to make the resolution 50 nm or less.
[0023]
Further, instead of connecting the capacitor to the photoelectric conversion plate, the photoelectric conversion plate may be integrally formed as one pole plate of the capacitor.
FIG. 5 is a drawing showing a capacitor formed by inserting a dielectric 11 between the photoelectric conversion plate 1 and the anode 2. The dielectric 11 is provided with a hole 12 connecting the portion of the photoelectric conversion plate 1 where the electronic image is formed and the opening of the anode 2 so that the secondary electron flow generated in the photoelectric conversion film is not obstructed. I have.
[0024]
In addition, a certain type of coaxial cable has a sufficiently large capacitance and a high resistance to a high voltage, so that it can be used as a capacitance element used in this embodiment without special measures.
In the above embodiment, the sample is set in close contact with the photoelectric conversion plate. However, the present invention is also applied to an X-ray microscope in which the sample is arranged apart and an X-ray transmission image is projected on the photoelectric conversion plate. The invention can be applied.
[0025]
【The invention's effect】
As described above, by using the laser plasma X-ray microscope of the present invention, an accurate electronic image can be obtained even when high-intensity pulsed X-rays are irradiated, and a living sample can be observed as an X-ray transmission image in a living state. Can be.
[Brief description of the drawings]
FIG. 1 is a partial configuration diagram showing one embodiment of a laser plasma X-ray microscope of the present invention.
FIG. 2 is a diagram showing the effect of the capacitor in the present embodiment.
FIG. 3 is a diagram illustrating a relationship between a voltage drop on a photoelectric conversion surface and a capacitance of a capacitor in the present embodiment.
FIG. 4 is an equivalent circuit diagram of a photoelectric conversion surface used for obtaining the diagram of FIG.
FIG. 5 is a partial configuration diagram showing another embodiment of the laser plasma X-ray microscope of the present embodiment.
FIG. 6 is a configuration diagram showing an example of a conventional laser plasma X-ray microscope.
FIG. 7 is a configuration diagram showing a photoelectric conversion part in a conventional laser plasma X-ray microscope.
FIG. 8 is a diagram illustrating a voltage drop on a photoelectric conversion surface in a conventional laser plasma X-ray microscope.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 photoelectric conversion plate 2 anode 3 sample 4 photoelectric conversion film 5 acceleration power supply 6 protection resistor 7 capacitor 8 coaxial cable 9 parallel capacitance 11 dielectric 12 hole

Claims (6)

What is claimed is: 1. A laser plasma X-ray microscope for converting an X-ray image into an electronic image by a photoelectric conversion film, and enlarging and observing the image with an electron optical system, comprising: A laser plasma X-ray microscope provided immediately adjacent to the photoelectric conversion film. 2. The laser plasma X-ray microscope according to claim 1, wherein the electric circuit for supplying the electric charge is configured with a capacitor as a main part. 3. The laser plasma X-ray microscope according to claim 2, wherein the capacitance element is a capacitor element interposed between the photoelectric conversion film and an anode or a ground terminal of the electron optical system. The capacitor element has a photoelectric conversion plate provided with the photoelectric conversion film as one electrode plate, a dielectric material is provided in close contact with the photoelectric conversion plate, and the other is provided on the other side of the photoelectric conversion plate with the dielectric material interposed therebetween. The laser plasma X-ray microscope according to claim 3, characterized by comprising: 5. The laser plasma X-ray microscope according to claim 4, wherein the other electrode plate is an anode of the electron optical system. 3. The laser plasma X-ray microscope according to claim 2, wherein the capacitance element is a coaxial cable connected to a photoelectric conversion surface.

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