JP2002303593A - X-ray analyzer - Google Patents

Abstract

(57) [Summary] [Problem] To properly measure an atmospheric state, a vacuum atmosphere state, and a helium gas atmosphere state with one apparatus. SOLUTION: The X-ray fluorescence analyzer 1 has a configuration including a measurement unit 2 and a movable unit 3, and the measurement unit 2 includes a first opening 2
b, a measurement chamber 2a having a b, an X-ray source 2c for irradiating primary X-rays toward the first opening, and an X-ray detector 2 for detecting secondary X-rays
e, a suction / exhaust means 2g for sucking / exhausting the inside of the measurement chamber, and a gas introduction means 2j for introducing a gas into the measurement chamber.
Has an open second opening 3a and a third opening 3b in which a thin film 3c is stretched, and individually aligns the second opening and the third opening with the first opening of the measuring unit. I do. By individually positioning the second opening or the third opening with respect to the first opening of the measuring unit, the measurement is performed in each state of the atmospheric state, the vacuum atmosphere state, and the gas atmosphere state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray analyzer used for analyzing the type, amount, and distribution of elements contained in a sample.

[0002]

2. Description of the Related Art An X-ray analyzer irradiates a sample with primary X-rays, detects secondary X-rays such as fluorescent X-rays and scattered X-rays generated by an X-ray detector, and generates a detection signal. Based on this, it is possible to analyze the constituent elements and the internal structure of the sample on the basis of this. For example, a fluorescent X-ray analyzer and an X-ray microscope are known.

[0003] As a method of performing elemental analysis using this X-ray analyzer, there is a method in which a sample is placed and an X-ray irradiation area where primary X-rays are irradiated is measured at atmospheric pressure. It is isolated from the atmosphere by being surrounded by a measurement chamber or the like, and a gas in which the absorption of primary X-rays or secondary X-rays is smaller than that of the atmosphere (for example,
There is a method of measuring in an atmosphere state (helium gas).

[0004] However, when performing fluorescent X-ray analysis in the atmosphere, there is a problem that it is difficult to detect light elements having a large absorption by the atmosphere, such as Na, Mg and Al. On the other hand, fluorescent X in vacuum or helium gas
When performing line analysis, it is necessary to exhaust or replace the gas in the measurement chamber every time the sample is replaced, which requires a long preparation time for the measurement and a long total analysis time. There is also a problem that it is not possible to measure a living body alive.

[0005] As an X-ray analyzer taking the above problems into consideration, an open type apparatus and a thin film type apparatus (for example, Japanese Patent Application Laid-Open No. 8-
No. 15187). The open type apparatus is provided with an opened opening in a measurement chamber, and performs measurement using the opening as an X-ray irradiation area. In this open type device,
Opening the opening allows measurement in the atmospheric state, or measurement with the helium gas flowing out from the measurement chamber to the atmosphere, with a part of the X-ray path in a helium gas atmosphere, facilitating sample exchange. It is assumed that.

Further, in the thin film type apparatus, a thin film having a low X-ray absorptivity is stretched in an opening provided in a measurement chamber, and the thin film is used to connect a first space in which an X-ray source and an X-ray detector are provided with a sample. It is divided into the second space where the stage is provided, and the first space is measured as an atmospheric state, a vacuum atmosphere state, or a gas atmosphere state, reducing the influence of atmospheric absorption,
This facilitates sample exchange and ensures detection of light elements such as Na, Mg, and Al.

[0007]

However, the open-type apparatus cannot set the X-ray path through which the primary X-rays and the secondary X-rays pass to a vacuum atmosphere state, so that the measurement in the atmospheric state or the helium gas It stops at the measurement in the atmosphere state. Therefore, there is a problem that it is not possible to detect light elements such as Na, Mg, and Al which have a large absorption by the atmosphere in the measurement in the atmospheric state, and in the measurement in the helium gas atmosphere state, there is a problem with the transition from the atmospheric state to the helium gas state. As a result, the mixing ratio between helium gas and the atmosphere fluctuates, and the intensity of the detected fluorescent X-ray fluctuates greatly.

The thin-film type device can be in any of the air state, the vacuum atmosphere state, and the helium gas atmosphere state. Therefore, it is possible to measure even a light element having a large absorption by the air, Since the provided thin film absorbs primary X-rays and secondary X-rays, there is a problem that the X-ray intensity of the secondary X-rays due to elements such as Na and Mg is reduced. Furthermore, when measuring in the atmospheric state, Si, P, S, etc. can be measured if the path to the detector is short, but it is absorbed by the thin film, so that it is compared with an open type device without a thin film. There is a problem that the X-ray intensity decreases.

[0009] Further, the problem of the decrease in the absorptivity of X-rays by the thin film and the problem of the influence of the fluorescent X-rays generated from the thin film are caused not only by the composition of the thin film itself but also by impurities such as a catalyst used when forming the thin film. It is also caused by the composition, and by the thin film, X
There is also the problem that the lines are scattered. Therefore, in the above-mentioned thin-film type device having a thin film fixed to the opening, the analytical performance is lower in the measurement in the atmospheric state than in the open-type device having no thin film. further,
In the thin film type device, the diameter of the opening for fixing the thin film needs to be small in order to withstand the pressure difference between the atmospheric pressure and the vacuum in the thin film portion. For this reason, there is also a problem that the observation range becomes narrow when observing visually or with an optical microscope through the opening.

[0010] Therefore, with the conventionally known X-ray analyzer, it is impossible to measure the atmospheric state, the vacuum atmosphere state, and the helium gas atmosphere state with one apparatus, or each state is measured with one apparatus. Even if it is possible, there is a problem in a decrease in the X-ray intensity in the atmospheric state and the helium gas atmosphere state, a decrease in the analytical performance due to a noise component of the secondary X-ray characteristic, or a narrow observation range in the sample observation.

Therefore, the present invention solves the above-mentioned conventional problems and provides an X-ray analyzer which can perform satisfactory measurement of the atmospheric state, the vacuum atmosphere state, and the helium gas atmosphere state with one apparatus. More specifically, when measuring in the atmospheric state and helium gas atmosphere state, the reduction and fluctuation of X-ray intensity are reduced, and the influence of secondary X-rays generated from the thin film itself is reduced. ,Also,
In sample observation, it is an object to provide an X-ray analyzer capable of obtaining a wide observation range.

[0012]

SUMMARY OF THE INVENTION The present invention provides a structure in which an opening of a measurement chamber can be selected from an open state and a state in which the opening is closed by a thin film. The above-mentioned apparatus is used to favorably perform measurements and observations of the atmospheric state, the vacuum atmosphere state, the gas atmosphere state, and the sample observation.

[0013] The X-ray fluorescence spectrometer of the present invention comprises a measuring section and a movable section. The measuring section includes a measuring chamber having a first opening and a primary X-ray beam directed toward the first opening. X to irradiate
A source, an X-ray detector for detecting secondary X-rays, and a suction / exhaust means for sucking / evacuating the inside of the measurement chamber, while the movable portion has an open second opening, and a third opening having a thin film stretched. The second opening and the third opening can be individually aligned with the first opening of the measuring unit. Then, the movable portion is individually positioned in the second opening or the third opening with respect to the first opening of the measuring portion, so that the movable portion is in an air state, a vacuum atmosphere state, or a gas atmosphere state. A measurement can be made.

When measuring the state of the atmosphere or observing the sample, the measurement chamber is brought into the air state by aligning the second opening with the first opening of the measuring section, and the primary X-ray and the secondary X-ray are irradiated. The measurement is performed in the atmospheric state, and the sample is observed visually or under an optical microscope in the atmospheric state. According to the measurement of the atmospheric state, the decrease in the X-ray intensity due to the thin film can eliminate the influence of noise and the like, and the limitation of the observation range due to the small diameter of the opening due to the installation of the thin film can be eliminated.

When the measurement of the vacuum atmosphere state is performed, the measurement chamber is shut off from the outside air by aligning the third opening with the first opening, and the measurement chamber is evacuated by the suction / exhaust means. The primary X-ray and the secondary X-ray are measured in a vacuum atmosphere at least in the measurement chamber.

When measuring the gas atmosphere state, the second opening and the third opening are aligned with the first opening in order, and first, the third opening is positioned at the first opening. After the measurement chamber is evacuated to outside by the intake / exhaust means and brought into a vacuum atmosphere state, the gas is introduced into the measurement chamber by the gas introduction means provided separately to make the gas atmosphere state. Then, by positioning the second opening to the first opening, the measurement chamber and the outside air are allowed to pass through, and measurement is performed in a state where gas flows out of the measurement chamber through the first opening and the second opening. According to the measurement of the gas atmosphere state, once the measurement chamber is in a vacuum atmosphere state, the air component is excluded and only the gas component is used. Variations in the detected X-ray intensity due to variations in the mixing ratio between gas and atmosphere can be eliminated.

The movable part of the X-ray analyzer according to the present invention comprises:
In addition to the second opening and the third opening, an X-ray shield that can be aligned with the first opening of the measurement chamber is provided. By aligning the X-ray shield with the first opening of the measurement chamber, it is possible to prevent the primary X-ray emitted by the X-ray source from leaking out of the measurement chamber during non-measurement. This also eliminates the need to stop the X-ray source in order to prevent leakage of the primary X-ray during non-measurement, and prevents a change in the intensity of the primary X-ray due to repeated driving / stopping of the X-ray source, thereby achieving stable The obtained primary X-ray intensity can be obtained.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic diagram for explaining the outline of the X-ray analyzer of the present invention. The X-ray analyzer 1 irradiates a sample S placed on a sample stage 4 with primary X-rays, and measures a secondary X-ray such as a fluorescent X-ray emitted from the sample S, and a measuring unit. A movable section for selectively aligning the opening and the thin film with respect to the provided opening;

The measuring section 2 includes an X-ray source 2c for irradiating primary X-rays and an X-ray source 2 as a measuring mechanism for performing X-ray analysis of the sample S.
X-ray introduction mechanism 2 installed between c and the irradiation position of sample S
d, Fluorescence X generated from sample S by primary X-ray irradiation
X-ray detector 2e for detecting secondary X-rays such as X-rays, and sample S
Optical equipment such as a CCD camera 2f for optically observing the camera. In addition, as the X-ray introduction mechanism 2d, a collimator for limiting the irradiation diameter of the primary X-ray, an X-ray for condensing the X-ray,
It can be a line conduit or a polycapillary.

The above-mentioned measuring mechanism is attached to the measuring chamber 2a. The measurement chamber 2a is provided with a wall that shields X-ray leakage to the outside and withstands atmospheric pressure when the inside is evacuated.
A first opening 2b for passing the primary X-rays and the secondary X-rays is formed at the irradiation position of the X-ray. In addition, the measurement room 2a
Is a vacuum exhaust mechanism 2h for evacuating the measurement chamber 2a to a vacuum atmosphere state and an air purging mechanism 2i for purging the inside of the measurement chamber 2a with the atmosphere. Means 2g and gas introduction means 2j for introducing a gas such as helium gas into the measurement chamber 2a are provided.

The movable section 3 includes a third opening 3b having an open second opening 3a and a thin film 3c, and a driving means 3d for driving the second opening 3a and the third opening 3b. The second opening 3a and the third opening 3b are individually aligned with the first opening 2b by moving the second opening 3a and the third opening 3b by the driving means 3d. The movement of the driving unit 3d can be controlled by a control unit (not shown), and the driving unit 3d can take any form of linear movement or rotational movement.

The second opening 3a is formed so as to be open, and allows primary X-rays and secondary X-rays to pass through both openings by being aligned with the first opening 2b on the measurement chamber 2a side. Can be. A thin film 3c is stretched over the third opening 3b. The thin film 3c is desirably made of a material that has a low absorptivity for X-rays such as primary X-rays and secondary X-rays, does not generate fluorescent X-rays due to the composition of the film itself, and has a strength that can withstand a pressure of about atmospheric pressure. As a thin film of such a material, for example, a polyester resin film is known, and a few μm
The thickness can be about the same.

An O-ring 2k is provided around the first opening 2b of the measurement chamber 2a so as to surround the first opening 2b. The first opening 2b is closed by the thin film 3c stretched over the three openings 3b and the O-ring 2k, and the inside of the measurement chamber 2a is maintained in a sealed state. The O-ring may be provided so as to surround at least the third opening 3ba on the movable section 3 side.

The sample stage 4 is provided below the movable section 3, and arranges the sample S at a position facing the first opening 2b.
Further, the sample stage 4 has a structure in which the stage surface is movable, and the irradiation position of the primary X-ray can be adjusted by positioning the sample S supported on the stage surface. With the above configuration, the X-ray analyzer 1 of the present invention can switch the measurement chamber 2a between the open state and the closed state by driving the movable unit 3, and can measure the atmospheric state and the vacuum atmosphere state. Alternatively, the measurement of the gas atmosphere state can be performed by one apparatus.

Next, with reference to FIG. 2, each measurement operation of measurement of the atmospheric state, measurement of the vacuum atmosphere state, and measurement of the gas atmosphere state will be described. First, measurement of the atmospheric state will be described with reference to FIG. When the measurement is performed in the atmosphere, the atmosphere is introduced into the measurement chamber 2a by the atmosphere purge mechanism 2i, and the driving unit 3d of the movable unit 3 is driven to move the second opening 3a to the first side on the measurement chamber 2a side. It is aligned with the opening 2b. By aligning the second opening 3a with the first opening 2b, the inside of the measurement chamber 2a is in communication with the atmosphere through the first opening 2b and the second opening 3a.

According to this atmospheric condition, the CCD camera 2f
The surface of the sample S can be optically observed by an optical observation system such as visual observation or the like. Since the diameter of the opened second opening 3a provided on the movable portion 3 side does not need to be small in order to stretch the thin film 3c, it can be made sufficiently large for optical observation. The diameter can be approximately the same as that of the opening 2b.

In this atmospheric condition, the X-ray source 2c
The primary X-rays generated in step (1) pass through the X-ray introducing mechanism 2d, pass through the first opening 2b and the second opening 3a, and irradiate the sample S. At this time, since the thin film 3c is not stretched in the second opening 3a, the primary X-ray is irradiated to the sample S without reducing the X-ray intensity by the thin film absorption. In addition, secondary X-rays such as fluorescent X-rays generated from the sample S are also used to reduce the X-ray intensity of the primary X-rays due to thin-film absorption.
It can be detected by the line detector 2e.

Next, the measurement of the vacuum atmosphere state is shown in FIG.
This will be described with reference to FIG. When the measurement is performed in a vacuum atmosphere state, the driving unit 3d of the movable unit 3 is driven to align the third opening 3b in which the thin film 3c is stretched with the first opening 2b on the measurement chamber 2a side. As a result, the first opening 2b of the measurement chamber 2a is shut off from the atmosphere by the thin film 3c and the O-ring 2, and is kept in a sealed state. After closing the measurement chamber 2a, the measurement chamber 2a is evacuated by the evacuation mechanism 2h.
Vacuum the inside of the. Thereby, the inside of the measurement chamber 2a is brought into a vacuum atmosphere state.

In this vacuum atmosphere, the X-ray source 2c
The primary X-rays generated in step (1) pass through the X-ray introducing mechanism 2d, pass through the first opening 2b and the thin film 3c, and irradiate the sample S. At this time, since the space from the X-ray source 2c to the first opening 2b is in a vacuum state, the reduction of the X-ray intensity of the primary X-ray is reduced by the atmospheric portion between the first opening 2b and the thin film 3c, the thin film 3c, And the air portion between the thin film 3c and the sample S, and the measurement chamber 2
It is possible to prevent a decrease in X-ray intensity on a path passing through the inside of a.

Secondary X-rays such as fluorescent X-rays generated from the sample S pass through the thin film 3c and the first opening 2b and are measured by the X-ray detector 2e. At this time, since the first opening 2b is in a vacuum state from the X-ray detector 2e, the reduction of the X-ray intensity of the secondary X-ray is reduced by the atmospheric portion between the sample S and the thin film 3c, the thin film 3c, and the thin film 3c. It becomes an air portion between the opening 3b and the first opening 2b, and it is possible to prevent the reduction of the X-ray intensity of the secondary X-ray on the path passing through the inside of the measurement chamber 2a.

FIG. 2 shows the measurement of the gas atmosphere state.
This will be described with reference to (b) and (c). In FIG. 2B, when measurement is performed in a gas atmosphere state, the driving unit 3d of the movable unit 3 is driven, and the third opening 3b in which the thin film 3c is stretched is connected to the first opening 3b on the measurement chamber 2a side. 2b, the first opening 2b of the measurement chamber 2a is
It is shut off from the atmosphere side by c and the O-ring 2 and kept in a sealed state. After the measurement chamber 2a is closed, the inside of the measurement chamber 2a is evacuated by the evacuation mechanism 2h, and the inside of the measurement chamber 2a is brought into a vacuum atmosphere state. Thereby, the constituent components of the atmosphere can be removed from the inside of the measurement chamber 2a.

Next, in FIG. 2C, after the inside of the measuring chamber 2a is brought into a vacuum atmosphere state, the evacuation mechanism 2h is stopped, and a gas such as helium gas is introduced from the gas introducing means 2j into the measuring chamber 2a. I do. After the gas pressure in the measurement chamber 2a reaches at least the atmospheric pressure, the driving unit 3d of the movable unit 3 is driven to align the opened second opening 3a with the first opening 2b on the measurement chamber 2a side. . Since the second opening 3a is open and the gas pressure in the measuring chamber 2a is at least atmospheric pressure, the gas introduced from the gas introducing means 2j into the measuring chamber 2a is not supplied to the first opening 2b and the second opening 2b. It flows out of the measurement chamber 2a through the opening 3a. Thereby, the measurement room 2a
Of these, the gas atmosphere can be set in the vicinity of the first opening 2b and the second opening 3a, and on the X-ray path near the sample S.

By bringing the inside of the measurement chamber 2a into a vacuum atmosphere state and then into a gas atmosphere state, and by constantly flowing the gas through the opening through which the X-ray path passes, the mixing ratio of gas and air in the X-ray path always becomes stable. Can be maintained. In this gas atmosphere state, primary X-rays generated by the X-ray source 2c pass through the X-ray introduction mechanism 2d, pass through the first opening 2b and the second opening 3a, and are irradiated on the sample S. Secondary X-rays such as fluorescent X-rays generated from the sample S pass through the second opening 3.
a and passes through the first opening 2b and is measured by the X-ray detector 2e. At this time, a gas atmosphere state exists from the X-ray source 2c to the sample S and from the sample S to the X-ray detector 2e.
In this gas atmosphere state, the mixing ratio of the gas and the atmosphere is always stable, so that the X-ray intensity of fluorescent X-rays of light elements, such as Na, Mg, and Al, which have a large absorption by the atmosphere, is stably and sensitively. Can be measured well.

Next, another configuration of the movable portion provided in the X-ray analyzer of the present invention will be described with reference to FIG. Movable part 3
In addition to the above-described second opening 3a and the third opening 3b in which the thin film 3c is stretched, an X-ray shield 3e is provided so as to be able to be positioned with respect to the first opening 2b. In addition,
The configuration shown in FIG. 3 is the same as the configuration shown in FIG. 1 except for the X-ray shield 3e, and therefore, only the X-ray shield 3e will be described here. The X-ray shielding unit 3e is
a and the third opening 3b in which the thin film 3c is stretched,
It can be moved by the driving means 3d, and can be selectively positioned on the measurement chamber 2a side.

By aligning the X-ray shield 3e with the first opening 2b, the measurement room 2a is shielded from the outside by X-rays, and the measurement room 2a for primary X-rays emitted from the X-ray source 2c. Leakage to the outside can be prevented. By closing the first opening 2b with the X-ray shield 3e, it is possible to prevent leakage of X-rays other than at the time of measurement such as replacement of the sample S. Further, when the X-ray leakage is prevented by repeating the driving and stopping of the X-ray source 2c, the X-ray intensity of the generated primary X-ray may change with time, and the measured value may become unstable. According to the movable unit including the X-ray shielding unit 3e of the present invention, the state in which the X-ray source is driven can be maintained, so that the X-ray intensity of the primary X-ray can be stabilized.

The X-ray shielding portion 3e has a structure in which an X-ray shielding material is attached to a supporting member that supports the second opening 3a and the third opening 3b in the movable portion 3, and the supporting member itself is an X-ray shielding material. Or a configuration in which a fourth opening (not shown) is provided and an X-ray shielding material is fitted into the opening.

In the above configuration example, the O-ring is provided on the measurement chamber 2a side, but may be provided on the movable section 3 side. FIG. 4 is a diagram for explaining the installation of the O-ring.

FIG. 4A shows an example of the movable section 3 having a second opening 3a and a third opening 3b in which the thin film 3 is stretched.
The O-ring 2k is arranged so as to surround the third opening 3b. Thus, when the third opening 3b is positioned at a position facing the first opening 2b, the measurement chamber 2a is closed by the O-ring 2k and the thin film 3c.

FIG. 4B shows the second opening 3a and the thin film 3c.
This is an example of the movable unit 3 including the third opening 3b provided with the X-ray shield 3e and the O-ring 2k. The O-ring 2k is arranged so as to surround the third opening 3b and the X-ray shield 3e. Accordingly, when the third opening 3b or the X-ray shield 3e is positioned at a position facing the first opening 2b, the measurement chamber 2a is sealed by the O-ring 2k, the thin film 3c, and the X-ray shield 3e. State.

The number of the third openings provided in the movable portion of the present invention is not limited to one, and a plurality of the third openings can be provided. It can be configured and can be changed according to the sample to be analyzed. Further, the X-ray analyzer of the present invention can be applied to an analyzer that performs analysis by irradiating a sample with a primary X-ray, such as a fluorescent X-ray analyzer or an X-ray microscope.

According to the X-ray analyzer of the present invention, it is possible to measure elements such as Si, P and S which can be measured in the atmospheric state at the maximum sensitivity without absorption of a thin film, as in the conventional open type apparatus. In the case of measurement in a vacuum atmosphere state,
As in the case of the thin film type device, the measurement chamber can be brought into a vacuum state or a gas atmosphere state, so that both measurements can be performed by one device.

According to the X-ray analyzer of the present invention,
The line path is almost in a gaseous atmosphere state, the variation in the mixing ratio between the gas and the atmosphere can be reduced, and since there is no absorption in the thin film, the fluorescence of light elements such as Na, Mg, and Al that are highly absorbed by the atmosphere is reduced. X-ray intensity of X-rays can be detected stably and with high sensitivity.

[0043]

As described above, according to the X-ray fluorescence spectrometer of the present invention, the measurement of the atmospheric state, the vacuum atmosphere state, and the helium gas atmosphere state can be performed with a single apparatus. Further, when measuring in the atmospheric state and the helium gas atmosphere state, it is possible to reduce the decrease and fluctuation of the X-ray intensity, and to reduce the influence of the secondary X-ray generated from the thin film itself. Can obtain a wide observation range.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining an outline of an X-ray fluorescence spectrometer of the present invention.

FIG. 2 is a diagram for explaining each measurement operation of measurement of an atmospheric state, measurement of a vacuum atmosphere state, and measurement of a gas atmosphere state by the X-ray fluorescence spectrometer of the present invention.

FIG. 3 is a diagram for explaining another configuration of a movable section provided in the X-ray analyzer of the present invention.

FIG. 4 is a view for explaining installation of an O-ring in the X-ray analyzer of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... X-ray analyzer, 2 ... Measuring part, 2a ... Measuring room, 2b ...
1st opening part, 2c ... X-ray source, 2d ... X-ray introduction mechanism, 2e
... X-ray detector, 2f ... CCD camera, 2g ... Supply / exhaust means, 2h ... Vacuum exhaust mechanism, 2i ... Atmospheric purge mechanism, 2j
... gas introducing means, 2k ... O-ring, 3 ... movable part, 3a ...
Second opening 3b 3rd opening 3a, 3c thin film, 3d
... Drive means.

Claims (2)

[Claims] 1. A measurement chamber having a first opening, an X-ray source for irradiating primary X-rays toward the first opening, an X-ray detector for detecting secondary X-rays, and A measuring unit having a suction / exhaust means for sucking and discharging, a second opening that is opened, a third opening having a thin film stretched, and the second opening and the third opening are provided in the first opening. A movable portion for individually positioning the third opening portion with the first opening portion for measuring the atmospheric state or observing the sample by aligning the second opening portion with the first opening portion. An X-ray analyzer for measuring a vacuum atmosphere state by aligning with an opening. 2. The X-ray analyzer according to claim 1, wherein the movable unit has an X-ray shielding unit that can be positioned with respect to the first opening.