JP3361114B2 - X-ray generator - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray generator for heating a filament by energization to generate thermoelectrons, colliding the thermoelectrons with a target and radiating X-rays from the target. In particular, the present invention relates to an X-ray generator suitable for an X-ray apparatus such as an EXAFS apparatus that performs X-ray measurement while changing the wavelength of X-rays incident on a sample.

[0002]

2. Description of the Related Art Generally, an X-ray generator has a filament and a target arranged to face the filament. A current supply circuit is connected to the filament, and the current is supplied to the filament to heat the filament. This heating causes the filament to generate heat and generate thermoelectrons. High voltage between filament and target, eg 20-60K
V is applied, and the thermoelectrons generated in the filament are accelerated by the applied voltage and collide with the target. Due to this collision, X-rays are emitted from the target.

By the way, a spectral vibrational structure appearing in an X-ray absorption spectrum, so-called EXAFS:
Extended X-Ray Absorption
It is already known that there is an EXAFS measurement device as a device for analyzing the fine structure of a sample based on Fine Structure). Conventionally, this EXA
In the FS measurement device, many measurement examples in which tungsten (W) is used as the material of the filament have been reported. During the emission of X-rays, that is, during the generation of electrons from the filament, tungsten evaporates from the tungsten filament. The evaporated tungsten adheres to the surface of the target, and as a result, a large number of characteristic X-rays of tungsten, mainly L-rays, are generated from the target.

In the EXAFS measurement, continuous X-rays near the absorption edge of the sample are irradiated onto the sample while changing the wavelength, and the X-ray absorption spectrum of the sample, that is, the intensity ratio I ₀ / transmission X-ray intensity ratio I ₀ / I (I ₀ : intensity of X-ray incident on the sample,
(I: intensity of X-ray transmitted through the sample) is measured. Further, the intensity of the X-ray incident on the sample is monitored, and the amount of electricity supplied to the filament is controlled based on the monitoring result so that the intensity of the incident X-ray is always constant. As described above, when tungsten is used as the material of the filament, many characteristic X-rays of tungsten are generated from the target. However, if the wavelength of the characteristic X-ray is close to the X-ray absorption edge of the sample to be measured. Then, when the wavelength of the incident X-ray is changed in the EXAFS measurement, the wavelength of the incident X-ray may match the wavelength of the characteristic X-ray of tungsten. In such a case, the intensity of the incident X-ray is significantly increased at the wavelength of the characteristic X-ray, which makes it impossible to control the amount of electricity supplied to the filament, that is, the intensity of the incident X-ray. Therefore, the accuracy of EXAFS measurement in the vicinity of the characteristic X-ray has deteriorated.

In order to avoid the characteristic X-rays generated by the evaporation of the filament material adhering to the target from interfering with the precise measurement in the EXAFS measurement, it is used depending on the sample to be measured. Change the material of the filament. For example, tungsten and lanthanum hexaboride (L
It is only necessary to prepare two kinds of aB ₆ ) and use them properly according to the sample to be used as the measurement target.

However, when the filaments are used properly, there are the following problems. That is, in order to generate X-rays in the X-ray generator, it is necessary to heat the filament by energizing. In this case, the exothermic temperature of the filament for obtaining a predetermined amount of thermoelectrons varies depending on the filament material, and the current-carrying capacity to the filament also varies depending on the filament material. For example, for a tungsten filament, it is 2500-260.
It is necessary to generate heat to about 0 ° C, and for that reason, 12
It is necessary to energize with an energizing capacity of about V, 12A. On the other hand, in the case of LaB ₆ filament,
It is necessary to generate heat at about 1600 ° C, and for that reason, it is necessary to conduct electricity with a conducting capacity of about 3V, 30A. Since the current-carrying capacities of the respective filaments are different in this way, it is not possible to use a common current supply system for supplying current to them.

When it is attempted to energize each filament with different energizing capacities, if it is done based on the conventional technique, X in which individual filaments of different types are mounted
A method in which a plurality of X-ray generators are prepared and these X-ray generators are selectively used according to the sample can be considered.
However, in this method, an X-ray generator must be prepared for each filament, which is extremely uneconomical, and there is a problem that it is necessary to prepare a wide space for installation.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above problems, and filaments made of different materials can be mounted on the filaments, and those filaments can be mounted by a simple operation. It is an object of the present invention to provide an X-ray generator that can be operated with an appropriate current-carrying capacity and does not require a large space for installation.

[0009]

An X-ray generator according to the present invention comprises a tube voltage applying means for applying a voltage between a filament and a target, and a tube current supplying means for supplying a current to the filament. The filament is heated by the tube current supply means to heat the filament to generate electrons from the filament, and the voltage is applied between the filament and the target by the tube voltage applying means to accelerate the electrons. It is an X-ray generator that emits X-rays from the target by colliding with the target. The filament is replaceably arranged at a predetermined position, and the tube current supply means is arranged in the following constituent element, that is, in the power feeding path to the filament, and the individual energization corresponding to the type of filament is performed. It is characterized by having a plurality of filament transformers having a capacity and a switch for selecting one of the plurality of filament transformers and electrically connecting it to the filament.

[0010]

The filament is replaceable, and the filament suitable for the sample to be measured is installed at a predetermined position in the X-ray generator. Then, the switch is operated, or the switch is automatically switched in association with the filament replacement work to select a filament transformer suitable for the energizing capacity of the installed filament and connect it to the filament. As a result, each filament is always energized with an appropriate energizing capacity and emits a predetermined amount of thermoelectrons. In the X-ray generator, a plurality of filament transformers corresponding to the filaments to be replaced and a switch for switching between them are simply installed. Therefore, when preparing a plurality of X-ray generators with individual filaments. The installation space of the X-ray generator can be made narrower than that of.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of the X-ray generator according to the present invention. This X-ray generator has an X-ray tube 17, and inside the X-ray tube 17, a filament 1 and a target 2 arranged opposite thereto are provided.
The filament 1 is replaceably installed at a predetermined position in the X-ray tube 17, and the filaments 1 made of different materials can be replaced and installed. The replacement can be performed by any method. For example, a method of preparing a plurality of cassette type filament units and exchanging each unit, a method of exchanging each filament by fastening means such as a screw, and the like can be considered. In the case of the example, two types of filaments, that is, a LaB ₆ filament and a tungsten filament, are used. The target 2 is made of, for example, copper (Cu).

A tube voltage applying circuit 3 is electrically connected between the filament 1 and the target 2. The tube voltage application circuit 3 includes a tube voltage control circuit 5 that outputs a constant voltage.
And a high-voltage transformer 6 that boosts the output voltage thereof, and a rectifier circuit 7 that rectifies the output voltage of the transformer 6 into a DC voltage. With this tube voltage application circuit 3, a high DC voltage between the filament 1 and the target 2, for example, 20 to
60 KV is applied.

A tube current supply circuit 4 is electrically connected to the filament 1. The tube current supply circuit 4 includes a tube current control circuit 8 that outputs a constant current, a tungsten filament transformer 9W, a LaB ₆ filament transformer 9L, and a switch 10 having contacts A and B. . Tungsten filament transformer 9W
Has a current-carrying capacity suitable for causing the tungsten filament to generate heat, for example, 12V, 12A, and LaB
_The filament transformer 9L for ₆ has a current-carrying capacity suitable for heating the LaB ₆ filament, for example, 3V, 30
It has a current carrying capacity of A. The switch 10 is operated manually by an operator or automatically in association with the replacement work of the filament 1 to switch the connection terminals of the contacts A and B. In the illustrated state, the terminal on the tungsten filament transformer 9W side is connected to the power feeding path from the tube current control circuit 8 to the filament 1.

In the X-ray tube 17, a Wehnelt 11 is arranged between the filament 1 and the target 2. A bias voltage application circuit composed of a bias control circuit 12, a bias transformer 13, and a rectifier circuit 14 is connected to the Wehnelt 1. The bias voltage application circuit applies a bias voltage to the Wehnelt 11. Has become.

As shown in the figure, a high voltage transformer 6 and a rectifying circuit 7 which constitute the tube voltage applying circuit 3, a bias transformer 13 and a rectifying circuit 14 which constitute a bias voltage applying circuit, and a tube current supplying circuit 4 are constituted. Each element of the tungsten filament transformer 9W is housed in the high voltage transformer unit 15 to form one unit. Further, the contact A of the filament transformer 9L for LaB ₆ and the switch 10 which constitute the tube current supply circuit 4 is
It is housed in a sub-transformer unit 16 which is a separate body from the high-voltage transformer unit 15 to form one unit.

The operation of the X-ray generator having the above structure will be described below. First, it is assumed that a tungsten filament is selected as the filament 1 and is installed at a predetermined position in the X-ray tube 17. At this time, the contacts A and B in the switch 10 are set to the tungsten filament transformer 9W side as shown in the figure. In this state, the current output from the tube current control circuit 8 and having a capacity controlled to 12V and 12A by the tungsten filament transformer 9W is supplied to the filament 1. By this current supply, the tungsten filament generates heat at a predetermined temperature, for example, 2600 ° C., and a predetermined amount of thermoelectrons is emitted.

A high voltage, for example, 20 to 6 is applied between the filament 1 and the target 2 by the tube voltage applying circuit 3.
0KV is applied and tungsten filament 1
The above-mentioned thermoelectrons emitted from are accelerated by the applied voltage and collide with the target 2. In this case, the direction of travel of the electrons emitted from the filament 1 is controlled by the influence of the voltage applied to the Wehnelt 11, and the electrons collide with a predetermined region on the target 2. Due to this collision, X-rays are emitted from the target 2. This X-ray is, for example, EXA
In FS measurement, it is used as an X-ray source in the case where a material having an X-ray absorption edge at a wavelength largely separated from the characteristic X-ray wavelength of tungsten is used as a sample.

When the EXAFS measurement is performed on a sample whose X-ray absorption edge is in the vicinity of the characteristic X-ray wavelength of tungsten, the filament 1 is replaced with a LaB ₆ filament. Then, the contacts A and B of the switch 10 are switched to the LaB ₆ filament transformer 9L side. Switch 10 is filament 1
If it is switched in conjunction with the replacement of,
It switches automatically when the filament is replaced.

By switching the switch 10, the tube current is controlled.
LaB is provided in the power supply path from the control circuit 8 to the filament 1.₆ 
The filament transformer 9L is connected. Therefore, L
aB 6 For filament 1, LaB₆ For filament
Energization is performed with the current-carrying capacity of the lance 9L, for example, 3V, 30A.
Be played. As a result, LaB₆ Filament 1 is predetermined
Generates a certain amount of thermoelectrons by generating heat at a temperature of 1500 ° C, for example.
The target 2 emits X-rays.

Lanthanum (La) evaporates from the LaB ₆ filament 1 and adheres to the target 2. As a result, many lanthanum characteristic X-rays are generated from the target 2. However, the wavelength of the characteristic X-ray is significantly different from the wavelength of the characteristic X-ray of tungsten, and therefore, regarding the sample currently subjected to the measurement, the characteristic X-ray of lanthanum does not adversely affect the EXAFS measurement. Therefore, EXAFS measurement with high accuracy is performed.

As described above, in the X-ray generator shown in FIG. 1, since the two filament transformers 9W and 9L are provided, the filaments 1 made of different materials can be exchanged and used. Further, since the two transformers 9W and 9L are selected and used by switching the switch 10, all components other than the transformers 9W and 9L can be commonly used. Therefore, it is economical and X
The overall shape of the line generator can be reduced.

Further, the filament transformer 9L for LaB ₆ through which a large current flows has more filaments 1 than the filament transformer 9W for tungsten through which a small current flows.
It is connected to a position close to. This is to shorten the conducting path through which a large current flows as much as possible to improve safety.

In the case of an ordinary conventional X-ray generator in which the filament 1 is not scheduled to be replaced, the high voltage transformer unit 15 shown in FIG. 1 is connected to the filament 1, the target 2 and the Wehnelt 11. . If the sub-transformer 16 and the switch 10 are attached to this conventional type X-ray generator, the conventional type X-ray generator can be easily converted into the type of X-ray generator of the present invention in which the filament can be replaced. be able to.

Although the present invention has been described with reference to one embodiment, the present invention is not limited to that embodiment. For example, the X-ray apparatus that can use the X-ray generator according to the present invention is not limited to the EXAFS measurement apparatus,
It can be used in any X-ray device that needs to change the wavelength of the line.

Further, the number of filament transformers is not limited to two, and can be increased.

[0026]

According to the present invention, since a plurality of filament transformers having different energizing capacities are provided in one X-ray generator, it is possible to replace and use filaments of different materials in one X-ray generator. You can Since the configuration for enabling the exchange of the filaments is only the spare filament transformers and switches having different current carrying capacities, the overall shape of the X-ray generator does not become so large.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of an X-ray generator according to the present invention.

[Explanation of symbols]

1 Filament 2 Target 3 Tube voltage application circuit 4 Tube current supply circuit 9W Tungsten filament transformer 9L LaB ₆ filament transformer 10 Switch A, B switch contact

Front page continuation (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01J 35/06 H05G 1/00 G21K 5/02

Claims (4)

(57) [Claims] 1. A tube voltage applying means for applying a voltage between the filament and the target, and a tube current supplying means for supplying an electric current to the filament, wherein the tube current supplying means energizes the filament to generate the voltage. The filament is heated to generate electrons from the filament, and the voltage applied between the filament and the target by the tube voltage applying means accelerates the electrons to collide with the target to emit X-rays from the target. In the wire generator, the filament is arranged in a replaceable manner at a predetermined position, and the tube current supply means is arranged in a power feeding path to the filament and has an individual current-carrying capacity corresponding to the type of filament. A plurality of filament transformers and one of the plurality of filament transformers X-ray generator characterized by having it into filaments by selecting a switch for electrically connecting. 2. The X-ray generator according to claim 1, wherein a current path connecting the filament transformer with a large current amount and the filament is shorter than a current path connecting the filament transformer with a small current amount and the filament. . 3. The plurality of filament transformers are mutually
It is provided as a separate body in
Item 2. The X-ray generator according to item 2. 4. The plurality of filament transformers are mutually
Be housed in multiple separate units
The X-ray generator according to claim 3, which is characterized in that.