JP2012033451A - X-ray generator and method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize the generation of X-rays in an X-ray generator using an ultraviolet laser.SOLUTION: The method for generating X-rays comprises irradiating an ultraviolet laser receiving surface 21 of an electron beam emitting device 20 with an ultraviolet laser emitted from an ultraviolet laser generator 51, irradiating a metal piece 25 with an electron beam emitted from an electron beam emitting surface 23 which is different from the ultraviolet laser receiving surface 21 in the electron beam emitting device 20, and generating X-rays from the metal piece 25. The degeneration of the material of the ultraviolet laser receiving surface 21 is prevented by controlling the ultraviolet laser.

Description

  The present invention relates to an X-ray generation apparatus and method.

Developments to reduce the size of X-ray generators are underway in response to demands such as space saving, energy saving, portability, and minimizing the amount of X-ray exposure.
The X-ray generator accelerates the electron beam emitted from the electron source to a high energy by the high electric field generated by the high potential generation source, irradiates the metal piece with the electron beam, and emits the X-ray from the metal piece. The structure to be made is common.
For example, in the X-ray generator described in Patent Document 1, a small X-ray tube using a field emission carbon nanotube cathode as an electron source and a high-potential generator for applying a high-voltage ultrashort pulse to the X-ray tube In addition, high-frequency coaxial cables are used.
There has also been proposed an X-ray generator of a type in which a pyroelectric material is heated by a Peltier element to irradiate the copper pieces with electrons emitted from the pyroelectric material and emit X-rays from the copper pieces (non-patent document). 1)
See also Non-Patent Documents 2 to 4 as techniques related to the present invention.

Japanese Patent No. 3090910

Published online 31 January 2005 in Wiley InterScience. DOI: 10.1002 / xrs.800 Development of X-ray source using pyroelectric crystal and laser light, 44th X-ray analysis meeting, 18 October 2008, P21 Electron emission from Li 03 crystal induced by Nd: YAG laser The 57th Joint Lecture on Applied Physics Proceedings (2010) Electron emission form LiNO3 crystal excited by ultraviolet laser, J. Vac. Sci. Technol. B 28 (2), Mar / Apr 2010

All of the above X-ray generators achieve the demand for miniaturization, but according to the study of the present inventor, there are the following problems.
One application of a small X-ray generator is cancer treatment that is performed by inserting the X-ray generator into the body and irradiating cancer cells with linear X-rays. From this point of view, when a type using a field emission type carbon nanotube cathode is examined, since it is necessary to apply a high voltage to the cathode in this type, even if an insulating coaxial cable is used, there is a sense of resistance in use at the treatment site. .
In the type using a pyroelectric material, a pyroelectric material is placed on the Peltier element, and the pyroelectric material is heated by the Peltier element to emit electrons from the pyroelectric material. Therefore, a high voltage is not required for the voltage applied to the Peltier element. However, since the emission of electrons continues from the pyroelectric body in the heated state even during cooling, it becomes difficult to control on / off of X-ray generation. This is because it takes time to completely cool the entire pyroelectric material to the non-electron emission state.
In the methods disclosed in Non-Patent Document 3 and Non-Patent Document 4, it has been difficult to stably emit X-rays having sufficient intensity for cancer treatment, for example.

In the previous application (PCT / JP2010 / 002489), the present inventor has proposed a novel X-ray generator of a type that emits an electron beam from a pyroelectric material by irradiating the pyroelectric material with an ultraviolet laser.
The inventor has further studied the X-ray generation apparatus and has attempted to stabilize the generation of X-rays.

An object of the present invention is to stabilize the generation of X-rays in an X-ray generator of the type using an ultraviolet laser.
The present inventor has paid attention to the fact that the light receiving surface of the ultraviolet laser changes in the pyroelectric body when the pyroelectric body is irradiated with the ultraviolet laser. The discoloration may be caused by denaturation or desorption of the pyroelectric material itself, or by denatured adsorption of gas particles in the pyroelectric atmosphere. A substance that has been transformed by absorbing energy is easily ionized, and the potential on the ultraviolet light receiving surface of the pyroelectric material becomes unstable. As a result, it was thought that the potential of the surface opposite to the ultraviolet light receiving surface in the pyroelectric material, that is, the electron beam emitting surface might become unstable.

Therefore, the present inventor tried to stabilize the potential on the ultraviolet laser light receiving surface (first surface) by preventing the material from being denatured by the ultraviolet laser on the light receiving surface of the pyroelectric material. As a result, stable and strong X-ray generation could be observed.
That is, the first aspect of the present invention is defined as follows.
An ultraviolet laser generator,
An electron beam emitting device comprising an ultraviolet laser receiving surface for receiving an ultraviolet laser emitted from an external ultraviolet laser generator and an electron beam emitting surface, wherein the ultraviolet laser receiving surface and the electron beam emitting surface are different surfaces; ,
An X-ray generator comprising: a denaturation preventing means for preventing a substance on the ultraviolet laser light receiving surface from being denatured by the ultraviolet laser.

  According to the X-ray generator of the first aspect defined as described above, even if an ultraviolet laser is irradiated to an electron beam generating element (hereinafter, simply referred to as element) such as a pyroelectric material, the ultraviolet ray is irradiated. Since no material change occurs on the laser light receiving surface, that is, no ionization of the material occurs, the potential of the ultraviolet laser light receiving surface of the element is stabilized (not zero potential). As a result, the potential of the electron beam emission surface of the device is also stabilized, and the electron beam is stably emitted from the electron beam emission surface. This electron beam is irradiated onto the metal piece, and X-rays are emitted from the metal piece.

  The second aspect of the present invention is defined as follows. That is, in the X-ray generator defined in the first aspect, the anti-denaturation means includes an ultraviolet laser irradiation control device that sets the unit pulse intensity of the ultraviolet laser to 1,000 μjoule or less and the unit pulse width to 100 ns or less. .

According to the study of the present inventor, it is possible to prevent the substance from being denatured (ionized) on the ultraviolet laser receiving surface of the device by relatively reducing the intensity of the unit pulse of the ultraviolet laser. On the other hand, the width of the unit pulse of the ultraviolet laser is set to 100 ns or less, and the total amount of energy of the ultraviolet laser applied per unit time is ensured to be sufficiently large while keeping the intensity of the unit pulse low.
Here, the intensity of the unit pulse is assumed to be a strength that does not denature a substance (constituent substance of the element and a gas substance around the light receiving surface) that is considered to exist on the light receiving surface of the ultraviolet laser, and the total amount of energy of the ultraviolet laser applied per unit time is The amount is sufficient to emit an electron beam from the electron beam emitting surface.
The intensity of the unit pulse of the ultraviolet laser and the total amount of energy of the ultraviolet laser to be added per unit time can be appropriately set according to the material of the element and / or its atmosphere. It is preferable to set it to 000 μjoules or less and the unit pulse width to 100 ns or less. Each lower limit is limited by the wavelength of the ultraviolet laser and the oscillation frequency and the total amount of energy applied per unit time.

Examples of the element used in the present invention include LiNbO ₃ single crystal and LiTaO ₃ single crystal as pyroelectric materials. In addition, a ferroelectric substance such as PLZT (lead lanthanum zirconate titanate) can be used. According to the study of the present inventor, even if the device is irradiated with an ultraviolet laser controlled in this way, the temperature of the device hardly changes in principle. Note that although the temperature of the device sometimes increased due to misalignment of irradiation, etc., the amount of X-ray emission decreased.
In that case, the amount of X-ray emission was recovered by (1) stopping the irradiation of the ultraviolet laser, lowering the irradiation energy per unit time, and / or (2) cooling the element. (2) As a method for cooling the element, any method such as contacting a low-temperature substance (such as a Peltier element) with or close to the electron beam emitting element and circulating a refrigerant around the electron beam emitting element can be adopted. .
In order to control the temperature of the element, it is preferable to provide a thermometer for measuring the temperature of the element.
Further, according to the study by the present inventor, it has been found that by controlling the ultraviolet laser, the atmosphere of the ultraviolet laser receiving surface in the element is not particularly limited and may be exposed to the atmosphere. Even in this case, the electron beam emission surface of the device and the metal piece facing it need to exist in a vacuum.

  In the case of using an element in which the substance is markedly modified on the ultraviolet laser receiving surface, it is preferable to cover the ultraviolet laser receiving surface with a protective film that is stable to the ultraviolet laser and transmits the ultraviolet laser. As such a protective film, it is important to use a material that absorbs as little as possible with respect to the ultraviolet wavelength used. This prevents the temperature of the element from rising due to absorption of ultraviolet rays. For example, when ultraviolet light having a wavelength of 266 nm, which is a fourth harmonic wave of a YAG laser, is used, it is preferable to use an inorganic material that transmits 90% or more, such as synthetic quartz glass and magnesium fluoride. When this protective film is used, it is desirable to install a cooling function because of the slight ultraviolet absorption. The protective film is preferably a conductive film, or an insulator that is dielectrically polarized like a dielectric. Further, if the thickness of the protective film is less than or equal to nm, it is necessary to make even a slight contact with the conductive material. At this time, it is desirable to avoid contact of the conductive material itself with other conductors. Although the degree of necessity of this treatment varies depending on the resistivity of the conductor, it is desirable that the treatment is not possible as much as possible. In other words, it is necessary to create a situation where it is electrically insulated from the ground. This is because it is necessary to facilitate the movement of charges for compensating for the spontaneous polarization charge of the element from the outside easily and quickly. It also prevents sudden temperature changes caused by external disturbances via the conductor's ground wire.

  For example, a YAG laser oscillator can be used as the ultraviolet laser generator. Ultraviolet light generated by this ultraviolet oscillator is introduced into one end of an optical fiber for ultraviolet light, and the other end of the optical fiber is opposed to the ultraviolet laser receiving surface of the element. An ultraviolet ray generating laser diode or a light emitting diode made of a group III nitride compound semiconductor can also be used. When higher output is required, it is preferable to use an excimer laser transmitter.

  The wavelength of the ultraviolet laser is preferably 300 nm or less. This is because most of such short-wavelength ultraviolet rays are absorbed by the outermost surface of the pyroelectric material, so that high energy conversion efficiency can be secured. The wavelength of the ultraviolet laser is set to a wavelength having energy larger than the band gap energy of the electron beam emitting element to be used. It is preferable to irradiate the whole surface of the ultraviolet laser receiving surface of the electron beam emitting device with an ultraviolet laser with uniform intensity. This is to prevent denaturation of the substance due to energy concentration.

The ultraviolet laser is preferably applied to the surface opposite to the surface facing the metal piece in the electron beam emitter.
Thereby, the metal piece, the electron beam emitting element, and the ultraviolet ray generator can be arranged in series, and the assembly of the apparatus is facilitated.
When a rod-shaped pyroelectric body is used as an electron-emitting device, one end of the rod-shaped body is opposed to a metal piece, and the other end is irradiated with an ultraviolet laser.
In the electron beam emitting device, the surface facing the metal piece (electron emitting surface) can be finely processed to form protrusions on the surface, thereby promoting electron emission.
A thin plate of copper or a copper alloy can be adopted as the metal piece. Of course, a metal other than copper, such as aluminum or an aluminum alloy, can be used if X-rays can be emitted in response to the irradiated electrons.

  The member that supports the electron beam emitter can be arbitrarily selected as long as it does not affect the electron beam emission. For example, the side surface of the electron beam emitting element (a surface other than the ultraviolet laser receiving surface and the electron beam emitting surface) can be supported by an insulator. Further, the ultraviolet laser receiving surface may be fixed to the conductive support member in a single piece. In this case, it is preferable that the conductive support member be electrically floated (not grounded). By adopting such a configuration, the configuration of the apparatus is simplified, and it is possible to meet the demand for a reduction in size and weight.

It is a block diagram which shows the structure of the X-ray generator of embodiment of this invention. It is a block diagram which shows the structure of the X-ray generator of other embodiment. It is a block diagram which shows the energy conversion system of embodiment. It is a schematic diagram which shows the structure of the X-ray generator of an Example. It is an output chart of the X-ray generator of an Example. It is another output chart. It is an output chart when using a different pyroelectric material. It is another output chart. It is sectional drawing which shows the detail in a chamber. It is a chart which shows the output state of the X-ray in each connection state of a SUS board. The connection aspect of the pyroelectric body with respect to a SUS board, the output chart of an X-ray, and a temperature change are shown. The other connection aspect of the pyroelectric body with respect to a SUS board, the output chart of an X-ray, and a temperature change are shown. The other connection aspect of the pyroelectric body with respect to a SUS board, the output chart of an X-ray, and a temperature change are shown. The other connection aspect of the pyroelectric body with respect to a SUS board, the output chart of an X-ray, and a temperature change are shown. An apparatus for measuring the temperature and surface potential of a pyroelectric body when the pyroelectric body is irradiated with an ultraviolet laser having a unit pulse of mJ order is shown. 1 shows an apparatus for measuring the temperature and surface potential of a pyroelectric body when the pyroelectric body is irradiated with an ultraviolet laser having a unit pulse on the order of μJ. The surface potential of the pyroelectric material heated and allowed to cool is shown. The surface potential of the light receiving surface of the pyroelectric body when the heated and left-cooled pyroelectric body is irradiated with an ultraviolet laser of mJ order is shown. The surface potential of the electron beam emitting surface of the pyroelectric material when the heated and cooled pyroelectric material is irradiated with an ultraviolet laser of mJ order is shown. The surface potential of the ultraviolet laser receiving surface of the pyroelectric body when the heated / cooled pyroelectric body is irradiated with an ultraviolet laser of μJ order is shown. The surface potential of the electron beam emission surface of the pyroelectric material when the heated and cooled pyroelectric material is irradiated with an ultraviolet laser of μJ order is shown.

Embodiments of the present invention will be described below.
FIG. 1 is a schematic diagram showing a structure of an X-ray generator 1 according to an embodiment. The X-ray generator 1 is suitable for insertion into a human digestive organ or the like.
The X-ray generator 1 includes a head unit 10, a fiber unit 40, and a control unit 50.
The head unit 10 includes a cylindrical casing 11 having a recess 14. A beryllium X-ray transmission window 13 is provided at the center position of the front end surface of the housing 11. An ultraviolet laser transmission window 16 made of quartz glass capable of transmitting ultraviolet rays is disposed at the center of the bottom surface of the recess 14, and the inside of the housing 11 is maintained in a vacuum state of about 10 ⁻³ to 10 ⁻⁴ Torr. .
A columnar pyroelectric material (LiNbO ₃ single crystal) 20 and a copper piece 25 as an electron beam emitting element are arranged inside the housing 11. The ultraviolet transmissive window 16, the pyroelectric body 20, the copper piece 25, and the X-ray transmissive window 13 are disposed on the same axis.

In the figure, reference numeral 31 denotes a thermometer made of a thermocouple, reference numeral 33 denotes a Peltier element, reference numeral 35 denotes an X-ray detector, and reference numeral 37 denotes an optical device, which are connected to a connector 39 by lines 32, 34, 36, and 38, respectively. Yes. Each line includes a power supply line and a signal line as necessary. It is assumed that the optical device 37 includes a light source and a camera and is exposed from the housing 11. An LED light source can be used as the light source, and a CCD can be used as the camera. When the head unit 10 is inserted into the human digestive organ by the optical device 37, the state of the insertion destination can be visually observed.
The connector 39 is provided in the recess 14 of the housing 11 and is connected to the connect 45 of the fiber part 40.

The fiber portion 40 is obtained by inserting an optical fiber 43 and a line 46 into a fiber main body 41 that is widely used as a fiber portion of a stomach camera or the like. The optical fiber 43 is for ultraviolet rays, and for example, quartz glass can be used for the core portion. The line 46 includes a power line and a signal line.
The tip of the fiber portion 40 is fitted into the recess 14 of the head portion 10, and both are sealed with a gasket 48.

The controller 50 includes an ultraviolet laser generator 51 and its driver 52, and a controller 53 that controls the electrical devices 31, 33, 35, 37 and 39 in the head unit 10. Reference numeral 55 denotes a control device that controls the driver 52 and the controller 53.
The light emitting part of the ultraviolet laser generator 51 faces the optical fiber 43 at the base end of the fiber part 40, and the ultraviolet laser is incident on the optical fiber 43.
A YAG pulse laser transmitter can be used as the ultraviolet laser generator 51, and its output is limited by the driver 52. The wavelength of the ultraviolet laser is not particularly limited as long as the electron beam emitting device 20 can be activated (that is, the electron beam can be emitted from the device 20). Short is preferred.

Since the temperature of the electron beam emitting device 20 may be increased by the irradiation of the ultraviolet laser, in this example, the Peltier device 33 is disposed in the vicinity of the electron beam emitting device 20 and the Peltier device 33 is cooled to emit the electron beam. The element 20 is cooled. In order to increase the cooling efficiency, the Peltier device 33 may be brought into contact with the electron beam emitting device 20 through an insulator.
When the temperature of the electron beam emitting device 20 exceeds a predetermined temperature, the controller 53 supplies power to the Peltier device 33 to cool it when the temperature of the electron beam emitting device 20 exceeds a predetermined temperature, thereby cooling the electron beam emitting device 20. Can do. When the temperature of the electron beam emitting device 20 is cooled to a predetermined temperature, energization to the Peltier device 33 is stopped.
The same control can be performed by incorporating a heat exchanger for passing the refrigerant into the housing 11 and circulating the refrigerant through the fiber portion 40.

An X-ray detector 35 is disposed between the copper piece 25 and the ultraviolet window 13. The output of the X-ray detector 35 is monitored by the controller 53. When the amount of X-ray radiation exceeds a predetermined threshold and is larger than the predetermined amount, the controller 53 sends a signal to the control device 55, and the control device 55 sends a control signal to the driver 52. As a result, the driver 52 activates the shutter of the ultraviolet laser generator 51 to stop the emission of the ultraviolet laser 51, and lowers the output of the ultraviolet laser.
The case where the amount of X-ray radiation is larger than the predetermined amount exceeding the threshold is when the amount of X-ray radiation exceeds a predetermined radiation amount (threshold), or when X-rays are not originally emitted. This includes the time when X-ray emission is observed even in a trace amount.

FIG. 2 shows another example X-ray generator 60. The same elements as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted.
In the example of FIG. 2, the ultraviolet laser receiving surface 21 of the electron beam generating element 20 protrudes from the housing 11 to the outside in the head portion 61. Thus, even if the ultraviolet laser receiving surface 21 of the electron beam generator 20 is exposed to the atmosphere, generation of X-rays can be confirmed as in the example of FIG.
By protruding the ultraviolet laser light receiving surface 21 from the housing 11 to the outside as in this example, the light receiving surface 21 can be easily cleaned up during repeated use, so that the life of the head unit 60 is improved.

In each of the above examples, the configuration in which the pyroelectric body 20 is irradiated with the controlled ultraviolet laser and the electron beam is emitted from the pyroelectric body 20 constitutes a novel electron beam emitting apparatus.
In this invention, the principle that an electron beam is emitted from a pyroelectric body by irradiating the pyroelectric body with a controlled ultraviolet laser is currently being confirmed, but at least by controlling the irradiation of the ultraviolet laser, The ultraviolet laser receiving surface is not discolored at all. That is, the substance on the light receiving surface is not denatured at all, or the amount thereof is extremely small even if denatured. As a result, the potential of the light receiving surface is stabilized, and the potential of the electron beam emitting surface is also stabilized. Stable X-rays are emitted from the copper piece that has received a stable electron beam.

In order to prevent denaturation of the substance on the ultraviolet laser light receiving surface, it is conceivable to cover the light receiving surface with a protective film. This protective film transmits an ultraviolet laser and is stable to the ultraviolet laser. Further, the protective film is tightly adhered to the light receiving surface. This is to avoid a substance easily denatured by ultraviolet rays between the two.
Examples of the protective film include inorganic materials such as magnesium fluoride. Further, it is preferable that a protective film is also applied to the peripheral wall near the light receiving surface in the pyroelectric body.

When the electron-emitting device 20 is irradiated with a controlled ultraviolet laser, when the electron beam is stably emitted from the electron-emitting device, a high potential is generated on the electron-emitting surface of the electron-emitting device. In other words, the electron beam emitting element is not only an electron gun but also a high potential generating element. This high potential generated in the electron beam emitting device can be converted into other energy (heat, light, etc.) or signal.
FIG. 3 shows the system configuration for this purpose.
In FIG. 3, the same elements as those of FIG. In FIG. 3, reference numeral 70 denotes a converter that converts a voltage into other energy, and reference numeral 71 denotes a converter that converts a voltage into a signal. These converters 70 and 71 are connected to the electron beam emission surface 23 of the electron beam emitter 20. The electron beam emitting surface 23 is preferably covered with a conductor film 76.
On the other hand, it is preferable to protect the ultraviolet laser receiving surface 21 of the electron beam emitting element with a protective film 75 for preventing the surface from being modified.

Next, examples of the present invention will be described.
FIG. 4 is a schematic diagram illustrating a configuration of the X-ray generator 100 according to the embodiment.
That is, in the X-ray generator 100, a pyroelectric material (LiNbO ₃ ) 103 and a copper foil 104 are disposed as an electron beam emitting element in a chamber 101. The chamber 101 is decompressed to 5 × 10 ⁻⁴ Torr by the rotary vacuum pump 105. The chamber 101 includes a quartz window 107 for introducing an ultraviolet laser and a beryllium window 108 for emitting X-rays.
A YAG laser device 110 is used as the ultraviolet laser generator, and the laser light emitted from the YAG laser device 110 is diffused by the lens 113 so that the end surface of the pyroelectric body 103 has a circular shape with a cross section of 5 mm in diameter.
The intensity of the X-ray transmitted through the beryllium window 108 is measured by the GM counter 115.
When the irradiation intensity of the YAG laser was 1600 mW and a rectangular pulse of 30 kHz, X-ray generation could be observed as shown in FIG. In FIG. 5, the vertical axis represents the count number of the GM counter.

  In the experiment of FIG. 5, YAG laser is continuously irradiated. On the other hand, the result when the YAG laser beam is irradiated intermittently is shown in FIG. From FIG. 6, it can be seen that generation / stop of X-rays are synchronized with on / off of ultraviolet light.

7 and 8 show X-ray output results when LiTaO ₃ is used as the electron-emitting device in the apparatus shown in FIG.
Since the generated voltage increases as the pyroelectric coefficient increases, irradiation of LiTaO ₃ with a lower power than LiNbO ₃ is effective.
The pyroelectric coefficient becomes maximum at the temperature just before the Curie point.
LiTaO ₃ has a Curie point of LiNbO ₃ of 690 ° C. and 1200.

FIG. 9 is a detailed configuration diagram in the chamber 101 of the X-ray generator 1 of the embodiment. The same elements as those in FIG. 4 are denoted by the same reference numerals, and the description thereof is omitted.
In this example, through-holes 201 and 202 are formed in a pair of SUS plates 200, respectively, and the ultraviolet laser receiving surface of the pyroelectric body 103 is connected to the peripheral portion of the through-hole 201 of the SUS plate 200 on the ultraviolet irradiation side with a conductive material. Through. The copper foil 104 is fixed to the peripheral edge portion of the through hole 202 of the SUS plate 200 on the X-ray emission side. The pair of SUS plates 200 and 200 are fixed with insulating screws made of polycarbonate.

(1) When the SUS plate 200 on the ultraviolet irradiation side was grounded, generation of X-rays was not observed. Similarly, (2) generation of X-rays was not observed when the SUS plate 200 on the ultraviolet irradiation side was brought into contact with the chamber 101 and grounded through the chamber 101.
(3) On the other hand, generation of X-rays was observed when the SUS plate 200 on the ultraviolet irradiation side was not grounded.

FIGS. 11 to 14 show how the electron beam generating element 103 is attached to the SUS plate 200 and the X-ray generation effect when the SUS plate 200 on the ultraviolet irradiation side is not grounded as in (3) above. 11 to 14, the same elements as those in FIG. 9 are denoted by the same reference numerals, and the description thereof is omitted.
In the example of FIG. 11, as shown in FIG. 11A, the electron beam generating element 103 is attached to the SUS plate 200 via a synthetic quartz glass 301 and a conductive double-sided tape 301. In this example, the generation of X-rays was confirmed as shown in FIG. FIG. (C) shows the temperature change of the element 103.
There was a time lag of about 240 seconds (S0 = 300 seconds) from the irradiation of the ultraviolet laser to the generation of X-rays. Irradiation with the ultraviolet laser was terminated at time S1 (= 1000 seconds) shown in (B) and (C).

In the example of FIG. 12, an insulator (insulating double-sided tape 303) is interposed between the synthetic quartz glass 300 and the element 103 as shown in FIG. In this example, as shown in (B) and (C), although an increase in temperature was observed, generation of X-rays was not observed.
In the example of FIG. 13, as shown in FIG. 13A, an insulating double-sided tape 301 is interposed between the SUS plate 200 and the synthetic quartz glass 300. Even in this example, as shown in (B) and (C), although the temperature was increased, the generation of X-rays was not recognized.
In the example of FIG. 14, the element 103 is directly attached to the SUS plate 200 via the conductive double-sided tape 301. X-ray generation was observed in this example (see (B)). In addition, there was a time lag of about 240 seconds (S3 = 300 seconds) from ultraviolet laser irradiation to X-ray generation. Irradiation with the ultraviolet laser was terminated at time S4 (= 720 seconds) shown in (B) and (C).
From the results of FIGS. 11 to 14, it is understood that it is preferable to fix the ultraviolet light receiving surface to the conductor in a conductive state as a support mode of the pyroelectric body 103.
From the results in the case of FIGS. 11 to 14, it is also understood that the electron beam emission from the pyroelectric body 103, that is, the generation of X-rays is not due to the temperature rise of the pyroelectric body. This is because in the case of FIGS. 12 and 13, although the temperature rise is observed, the generation of X-rays was not detected.

Next, the results of examining the intensity of the ultraviolet laser are shown in FIGS.
FIG. 15 shows a device for measuring the surface potential and temperature when the pyroelectric body 103 is irradiated with an ultraviolet laser (mJ laser) having a relatively strong unit pulse intensity, and reference numeral 315 in the figure denotes a thermocouple as a thermometer. Reference numeral 318 denotes a surface electrometer. By holding the peripheral surface of the pyroelectric body 103 with a ceramic retainer 319, the temperature rise of the pyroelectric body 103 due to the ultraviolet laser is eliminated as much as possible.
FIG. 16 shows a state in which the pyroelectric body 103 is irradiated with an ultraviolet laser (μJ laser) having a relatively weak unit pulse, and the same elements as those in FIG. .
15 and 16, the unit time power of the ultraviolet laser is the same (400 mW).
The ultraviolet laser receiving surface of the pyroelectric body 103 that has received the ultraviolet laser of FIG. 15 has turned black, while no discoloration has been seen on the ultraviolet laser receiving surface of the pyroelectric body 103 that has received the ultraviolet laser of FIG.

FIG. 17 shows the relationship between the temperature of the pyroelectric body 103 used in FIGS. 15 and 16 and the surface potential on the ultraviolet laser receiving surface side. As shown in FIG. 17, when the pyroelectric body 103 is heated, its surface potential changes. Thereby, electrons on the surface can be emitted. Hot air from a commercially available dryer was used for heating.
As shown in FIG. 18, when the pyroelectric body 103 is irradiated with an ultraviolet laser having a relatively strong unit pulse intensity shown in FIG. The surface potential on the ultraviolet laser receiving surface side became zero. Similarly (see FIG. 19), the surface potential on the electron beam emission surface side was also zero.
In this state, the electron beam cannot be emitted.
In other words, when the surface of the pyroelectric body 103 is charged under the same heating conditions as in FIG. 17 (the original function of the pyroelectric body), irradiation with an ultraviolet laser under the conditions shown in FIG. The surface of the body 103 becomes zero volts, the electron beam is not emitted, and no X-rays are generated.

On the other hand, as shown in FIGS. 20 and 21, when the pyroelectric body 103 is irradiated with an ultraviolet laser having a relatively weak unit pulse intensity shown in FIG. The surface of the pyroelectric body 103 on the ultraviolet laser receiving surface side is in a charged state.
From the results of FIGS. 15 to 21, it can be seen that the energy of the ultraviolet laser affects the electron beam emission of the pyroelectric material, and hence the generation of X-rays.
The energy of the ultraviolet laser can be appropriately selected so that the surface of the pyroelectric body (electron beam emitting element) can be maintained in a charged state.
According to the study by the present inventor, it is preferable that the unit pulse intensity is 1,000 μjoules or less and the unit pulse width is 100 ns or less.
Moreover, even if the intensity of the unit pulse is 1 to 100 mJ, the unit pulse width is set to psec or fsec, or the pyroelectric surface is prevented from being denatured by sufficiently providing a cooling effect, and the charge state of the surface is changed. It can be secured. However, the pulse energy of mJ is not practical because it is difficult to transmit with the current optical fiber.

  The present invention is not limited to the description of the embodiments and examples of the invention described above. Various modifications may be included in the present invention as long as those skilled in the art can easily conceive without departing from the description of the scope of claims.

DESCRIPTION OF SYMBOLS 1, 60, 100, 110 X-ray generator 10 Head part 11 Case 13 X-ray transmissive window 16 Ultraviolet laser transmissive window 20, 103 Electron beam emitting element 21 Ultraviolet laser light-receiving surface 23 Electron beam emitting surface 25, 104 Metal piece 41 Fiber part 43 Optical fiber 51 Ultraviolet laser oscillator

Claims (12)

An ultraviolet laser generator for generating an ultraviolet laser having a unit pulse intensity of 1000 μjoule or less and a unit pulse width of 100 ns or less;
An electron beam emitting device comprising an ultraviolet laser light receiving surface for receiving the ultraviolet laser emitted from the ultraviolet laser generator and an electron beam emitting surface, wherein the ultraviolet laser light receiving surface and the electron beam emitting surface are different surfaces. When,
A metal piece that receives an electron beam emitted from the electron beam emitting surface and emits an X-ray;
An X-ray generator comprising:   2. The X-ray generator according to claim 1, wherein the ultraviolet laser receiving surface of the electron beam emitting element exists in an air atmosphere. A thermometer for detecting the temperature of the electron beam emitting element;
A cooling device for cooling the electron-emitting device,
The X-ray generator according to claim 1 or 2, wherein the cooling device is operated based on a detection result of the thermometer to adjust a temperature of the electron beam emitting element. An X-ray detector for detecting the X-rays emitted from the metal piece;
An ultraviolet laser cutoff device for stopping the output of the ultraviolet ray generator,
4. The ultraviolet laser blocking device stops emission of the ultraviolet laser from the ultraviolet laser generator when an unscheduled X-ray is detected by the X-ray detector. Any X-ray generator.   5. The denaturation preventing means is formed of a protective film that covers the ultraviolet laser light receiving surface of the electron beam emitting element and is stable to and transmits the ultraviolet laser. The X-ray generator in any one of.   6. The X-ray generator according to claim 5, wherein the protective film conductor is conductive and insulated from the ground. An ultraviolet laser emitted from an ultraviolet laser generator is irradiated on an ultraviolet laser receiving surface of an electron beam emitting element, and an electron beam emitted from an electron beam emitting surface different from the ultraviolet laser receiving surface in the electron beam emitting element In the X-ray generation method of generating X-rays from the metal piece,
An X-ray generation method, characterized in that an ultraviolet laser is controlled to prevent denaturation of a substance on the ultraviolet laser receiving surface.   8. The X-ray generation method according to claim 7, wherein the output of the controlled ultraviolet laser has a unit pulse intensity of 1,000 μJ or less and a unit pulse width of 100 ns or less.   The X-ray generation method according to claim 7, wherein the ultraviolet laser receiving surface of the electron beam emitting device is charged by the controlled ultraviolet laser.   The X-ray generation method according to claim 7, wherein the ultraviolet laser receiving surface is in an air atmosphere.   11. The X-ray generation method according to claim 7, wherein the ultraviolet laser light receiving surface is protected by a protective film that is stable and transparent to the ultraviolet laser.   A method for controlling a potential of the second surface of a dielectric element having a function of emitting an electron beam from a second surface by irradiating an ultraviolet laser onto the first surface, the method comprising: 1 surface is irradiated with an ultraviolet laser having a unit pulse intensity of 1,000 μJ or less and a unit pulse width of 100 ns or less to maintain the first surface in a charged state. How to control the potential.