JP2013004246A - X-ray source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an X-ray source capable of suppressing generation of an electron beam with a large current amount to prevent damage of an electron source.SOLUTION: An X-ray source 10 houses an electron source 22 in a vacuum container 14 having a transparent target 17. A high voltage is applied from a high-voltage power supply 29 of a power supply circuit 12 to the electron source 22 to generate an electron beam 21 that irradiates the transparent target 17 from the electron source 22. Protection means 36 is installed between the high-voltage power supply 29 and the electron source 22 to restrict an electron beam current amount by the protection means 36.

Description

  Embodiments of the present invention relate to an X-ray source that generates X-rays.

  A general X-ray source having a micro focus has already been commercialized as a micro focus X-ray source, and is widely used in a non-destructive inspection apparatus for inspecting a micro area of an object with high resolution. In this X-ray source, the electron beam emitted from the electron source is converged by an electron optical system such as an electric field lens or a magnetic field lens, and is incident on a narrow region of the order of μm or less on the surface of the transmission target. A configuration is adopted in which X-rays are generated by the transmission target, and the generated X-rays are transmitted through the transmission target and emitted.

  Here, in order to measure a minute substance, it is necessary to reduce the generation of X-rays to a minute aperture, and it is necessary to focus an electron beam to a minute aperture on a transmission target that is an X-ray generation source. For this purpose, an electron source, an extraction electrode for applying a high voltage for making electrons flow into a beam, an acceleration electrode for applying a high voltage for applying energy to the electron beam, and an electron beam in a vacuum vessel maintained at high vacuum Therefore, it is necessary to have a configuration such as a lens electrode that applies a high voltage for converging the light to a small aperture.

JP 2008-140687 A

  By the way, since the generated X-ray dose is proportional to the amount of electron beam, that is, the amount of electron beam current, in order to obtain a predetermined X-ray dose, it is necessary to flow a current corresponding thereto, but the electron beam is converged to a small aperture. As a result, the current density of the electron beam increases, the transmission target on which the electron beam is incident is overheated, and the gas contained in the transmission target is scattered in the vacuum container, which may greatly reduce the internal resistance in the vacuum container. . The generated gas is a residual gas when a metal transmission target such as hydrogen, oxygen, or argon gas is manufactured.

  When the gas scatters in the vacuum container maintained at a high vacuum, the resistance value in the vacuum container is lowered, so that a large current amount of electron beam may be generated and the electron source may be damaged.

  The problem to be solved by the present invention is to provide an X-ray source capable of preventing the electron source from being damaged by suppressing generation of an electron beam having a large current amount.

  The X-ray source of this embodiment stores an electron source in a vacuum vessel provided with a transmission target. A high voltage is applied to the electron source from a high-voltage power supply of the power supply circuit, and an electron beam that irradiates the transmission target from the electron source is generated. A protective means is installed between the high voltage power source and the electron source, and the amount of electron beam current is limited by the protective means.

It is a block diagram of the X-ray source which shows 1st Embodiment. It is sectional drawing of the X-ray tube main body of an X-ray source same as the above. It is sectional drawing of the connector connected to the X-ray tube main body of an X-ray source same as the above. It is a graph which shows the change of the emission current which flows into the electron source of an X-ray source same as the above. It is sectional drawing of the connector connected to the X-ray tube main body of the X-ray source which shows 2nd Embodiment.

  Hereinafter, a first embodiment will be described with reference to FIGS. 1 to 4.

  As shown in FIG. 1, the X-ray source 10 is used for measuring a substance that needs to be measured with low energy X-rays such as a resin having a very small shape and relatively high X-ray transmittance, for example, X-ray tomography. The present invention is used for a stereoscopic image forming apparatus having an X-ray CT (Computed Tomography) apparatus as an imaging apparatus.

  The X-ray source 10 includes an X-ray tube main body 11 and a power supply circuit 12 that drives the X-ray tube main body 11.

  As shown in FIGS. 1 and 2, the X-ray tube main body 11 has a cylindrical vacuum container 14 in which the inside is held in vacuum. The vacuum container 14 has a metal container body 15, a transmission target 17 for emitting X-rays 16 to the outside is disposed at one end of the container body 15, and an insulating portion 18 is disposed at the other end of the container body 15. A support portion 19 is disposed through the support portion 19. The support portion 19 is formed with a concave connector receiving portion 20.

  An electron source 22 that generates an electron beam 21 toward the transmission target 17 is disposed on the other end side in the vacuum vessel 14, and a pair that is connected to both ends of the electron source 22 to heat the electron source 22. Heaters 23a and 23b are arranged. These heaters 23a and 23b penetrate the connector receiving portion 20 and are supported by support terminals 24a and 24b for inputting current from outside the vacuum vessel 14.

  The transmission target 17 is formed by using, for example, beryllium having a small attenuation of the X-ray 16 as a structural material, and coating a metal material such as tungsten that emits the X-ray 16 when the electron beam 21 is incident on the surface thereof.

  Although not shown in the drawings, the vacuum vessel 14 has an extraction electrode that extracts the electron beam 21 from the electron source 22, an acceleration electrode that accelerates the electron beam 21, and a lens electrode that converges and irradiates the transmission target 17 with the electron beam 21. Is installed.

  The power supply circuit 12 includes a power supply 26 and a wiring device 27 that connects the power supply 26 and the X-ray tube main body 11.

  The power source 26 is a heater power source 28 that is a DC stabilized power source for heaters that supplies a heater heating current to the heaters 23a and 23b, and a high voltage DC stabilized power source that applies a high voltage (about 30 kV) to the electron source 22. A voltage power supply 29 is provided. A capacitor 30 for reducing ripple is connected to the high voltage power supply 29.

  As shown in FIGS. 1 and 3, the wiring device 27 includes a connector 31 connected to the connector receiving portion 20 of the X-ray tube main body 11, and a cable 32 connecting the connector 31 and the power supply 26.

  The connector 31 includes a pair of connection terminals 33a and 33b connected to the pair of support terminals 24a and 24b, a pair of voltage dividing resistors 34a and 34b having one end connected to the pair of connection terminals 33a and 33b, A protective resistor 35 having one end connected to the connection point of the other end of the piezoresistors 34a and 34b is disposed. A protective resistor 35 is installed between the high-voltage power supply 29 and the electron source 22 and is configured as a protective means 36 that limits the amount of electron beam current.

  The cable 32 includes a heater power supply 28, cables 37a and 37b connecting the connection terminals 33a and 33b of the connector 31 and the voltage dividing resistors 34a and 34b, and the high voltage power supply 29 and the other end of the protective resistor 35. A cable 38a to be connected and a cable 38b to connect the container body 15 having the ground potential are provided.

  Next, the operation of the X-ray source 10 will be described.

  A heater heating current is supplied from the heater power supply 28 to the heaters 23a and 23b, and the electron source 22 is heated by the heaters 23a and 23b.

  A high voltage is applied from the high voltage power supply 29 to the electron source 22. That is, between the electron source 22 from the high voltage power source 29 through the cable 38a, the protective resistor 35, the voltage dividing resistors 34a and 34b, the heaters 23a and 23b, and the transmission target 17 provided in the container body 15 at the ground potential. A high voltage is applied to. As a result, thermoelectrons are generated from the electron source 22, and the generated thermoelectrons are extracted as an electron beam 21 by the extraction electrode. The electron beam 21 is accelerated by the acceleration electrode and converged to a minute aperture by the lens electrode and transmitted. Incident on the target 17. As a result, X-rays 16 are emitted from the transmission target 17, and the emitted X-rays 16 pass through the transmission target 17 and are emitted to the outside.

  By the way, when performing transmission imaging using X-rays 16, since the imaging resolution capability is improved by making the X-ray generation source have a small aperture, it is desirable to reduce the aperture of the electron beam 21 that converges and irradiates the transmission target 17. ing. However, if the aperture of the electron beam 21 that converges and irradiates the transmission target 17 is reduced, the current density of the electron beam 21 increases, and the transmission target 17 is heated to a very high temperature. Spatters into the vacuum container 14. The resistance value in the vacuum container 14 is greatly reduced by the gas scattered in the vacuum container 14, and as shown by the broken line in FIG. 4, a large current amount of electron beam 21 is generated from the electron source 22. Risk of damage.

  Therefore, in this embodiment, since the protective resistor 35 is used as the protective means 36 that is installed between the high-voltage power supply 29 and the electron source 22 and limits the amount of electron beam current, the transmission irradiated with the electron beam 21 is performed. Even if the gas scatters from the target 17 into the vacuum vessel 14 and the resistance value in the vacuum vessel 14 decreases, the protection resistor 35 restricts the electron beam current from increasing greatly as shown by the solid line in FIG. And damage to the electron source 22 can be prevented.

  In addition, since the protective resistor 35 is installed on the connector 31, the maximum value of the current of the electron beam 21 is reduced by the protective resistor 35 against the energy due to the charge stored in the floating capacitor generated in the cable 32. be able to. This current value is determined by the voltage of the high voltage power supply 29, the voltage supplied by the ripple reducing capacitor 30 connected to the high voltage power supply 29, and the resistance value in the vacuum vessel 14, but the vacuum The rate of decrease of the discharge resistance due to gas generation in the container 14 is large, and the voltage applied to the vacuum container 14 by the cable 32 and the protective resistance 35 is decreased, so that the actual value of the electron beam current can be reduced.

  The larger the resistance value of the protective resistor 35 is, the greater the protective function is. However, if the resistance value is too large, the voltage value applied to the vacuum vessel 14 is fluctuated due to fluctuations in the electron beam 21, and therefore, for example, a range of 50 to 100 kilohms is preferable.

  A second embodiment is shown in FIG. In addition, about the same structure as 1st Embodiment, the description is abbreviate | omitted using the same code | symbol.

  The voltage dividing resistors 34a and 34b may be used as the protection means 36. Also in this case, as in the first embodiment, voltage dividing resistors 34a and 34b are used as protection means 36 that is installed between the high-voltage power supply 29 and the electron source 22 and limits the amount of electron beam current. Therefore, even if gas scatters from the transmission target 17 irradiated with the electron beam 21 into the vacuum vessel 14 and the resistance value in the vacuum vessel 14 decreases, the electron beam current greatly increases. 34b can be regulated, and damage to the electron source 22 can be prevented. Furthermore, compared with the first embodiment, the configuration can be simplified because the protective resistor 35 can be omitted.

  The protection means 36 is not limited to being disposed in the connector 31, and may be disposed in the cable 38a in the vicinity of the connector 31.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

10 X-ray source
12 Power supply circuit
14 Vacuum container
17 Transmission target
20 Connector receptacle
21 Electron beam
22 electron source
23a, 23b Heater
29 High voltage power supply
31 Connector
32 cable
34a, 34b Voltage divider resistor
35 Protection resistance
36 Protective measures

Claims (5)

A vacuum vessel with a transmission target;
An electron source that is housed in the vacuum vessel and generates an electron beam that irradiates the transmission target;
A high-voltage power source that generates an electron beam by applying a high voltage to the electron source, and a power supply circuit that is installed between the high-voltage power source and the electron source and has protection means for limiting the amount of electron beam current. An X-ray source comprising: A pair of heaters connected to the electron source for heating the electron source;
The protective means includes a pair of voltage dividing resistors connected to the pair of heaters, and a high voltage is applied from the high voltage power source to a connection point of the pair of voltage dividing resistors. The X-ray source according to 1. The X-ray according to claim 2, wherein the protection means includes a protection resistor connected between the pair of voltage dividing resistors, and a high voltage is applied to the protection resistor from the high-voltage power supply. source. The vacuum vessel has a connector receiver connected to the electron source,
The power supply circuit has a cable connected to the high-voltage power supply, and a connector provided at a tip of the cable and connected to the connector receiving portion,
The X-ray source according to claim 1, wherein the protection means is disposed on the connector. The vacuum vessel has a connector receiver connected to the electron source,
The power supply circuit has a cable connected to the high-voltage power supply, and a connector provided at a tip of the cable and connected to the connector receiving portion,
The X-ray source according to any one of claims 1 to 3, wherein the protection means is disposed on the cable in the vicinity of the connector.

Images