DE9007499U1 - Device for generating and measuring the secondary radiation emitted by a sample irradiated with X-rays - Google Patents

Description

Dr. Dieter Weber

Dipl.-Chem.

Klaus Seiffert

Dipl.-Phys.

Dr. Winfried Lieke

Dipl.-Phys.

Weber, Seiffert. Lieke · Patent Attorneys · PO Box 6145 · 6200 Wiesbaden

Patent attorneys

Gustav-Freytag-Strasse 25

6200 Wiesbaden-1

Telephone 0611 / 37 27 20 and 37 25 80

Telex 4-186247

Fax 0611/372111

Telegram address: Willpatent

Date:

11 Dec. 1991 Sf/I/Sa

ROENTG91.001

X-ray analysis measuring technology GmbH

Georg-Ohm-Strasse 6
Taunusstein-Neuhof

Device for generating and measuring the voltage generated by a X-ray irradiated sample outgoing Secondary radiation

The present innovation relates to a device for generating and measuring secondary radiation, which emanates from a sample irradiated with X-rays. Such a device essentially has the following features:

an X-ray tube in a housing that is essentially impermeable to X-rays,

an opening in the housing for the exit of an X-ray beam,

a collimator to limit the X-ray radiation to a certain, fixed

Postgiro: Frankfurt/M 6763-602
Bank: Dresdner Bank AG. Wiesbaden Account 27680700 (bank code 51080060)

defined area,

a shutter between the X-ray tube and the collimator, which can interrupt the X-ray beam, for example, to change the sample,

an adjustment device for setting the desired point of impact of the X-rays and

a proportional counter tube or the like for detecting the secondary radiation emitted by the irradiated sample.

When the shutter is open, the collimator then filters out an X-ray beam from the radiation emitted by the X-ray tube, which beam impinges on a small area of a sample to be measured, whereby, if necessary, the proportional counter tube or another device for detecting the secondary radiation is aligned with the irradiated area of the sample and thus detects the secondary radiation emitted from this area.

Such devices are well suited, for example, for determining the thickness of very thin layers by measuring the fluorescence radiation emanating from the irradiated sample area.

The samples to be examined are often very small and the surfaces to be examined are not always homogeneous, so that the result of a secondary radiation measurement often depends very much on the precise knowledge of the area of the surface on which the X-rays hit. On the other hand, this area is not easily recognizable, since both the X-rays and (in general) the secondary radiation are invisible.

For this reason, such devices generally have an adjustment device which uses aids to indicate the alignment of the X-ray beam and its point of impact on a sample. However, these adjustment devices, which for example project a beam of light onto the supposed point of impact of the X-rays, are not very precise and can easily be misaligned without the incorrect adjustment being immediately apparent, and in addition, the adjustment often requires the collimator to be at a certain distance from the sample.

In contrast, the present invention is based on the object of creating a device of the type mentioned at the outset in which misalignment is practically impossible and in which the adjustment process can be carried out much more easily and with high precision.

This task is solved by the collimator itself forming part of the adjustment device. Although the adjustment device and collimator are occasionally coupled together in known devices of this type, the collimator itself does not play an active role in the adjustment and the connection between the adjustment device and the collimator only serves to fix a reference point for the adjustment device. The present invention differs from this in that the collimator itself is used directly as part of the adjustment device.

According to a preferred embodiment of the invention, this is done by providing a device by means of which a light beam is guided through the collimator bore when the shutter is closed.

Such a light beam can advantageously serve as a pointer, whereby this light beam emerging from the collimator creates a light spot exactly at the point where the X-ray beam, which takes the same path through the collimator, must also hit. This is particularly true if the collimator has a relatively long bore with a small diameter and/or is a large distance from the X-ray tube.

Conversely, however, the sample can also be illuminated, whereby part of this light is also reflected into the collimator bore and can be viewed, for example, through a mirror optics mounted above the collimator; in this way, the point of impact of the X-rays could also be identified.

However, an embodiment of the invention is preferred in which the device for passing a light beam through the collimator bore has a direct or indirect light source arranged on the shutter. '

An indirect light source is understood to be, for example, a mirror that reflects the light coming from another light source into the collimator bore. However, an active light source, e.g. a light-emitting diode, a light bulb or a laser, could also be arranged on the shutter itself.

Of course, the light source could also be in operation when the shutter is open, so that the area of a sample exposed to X-rays is optically visible even during the measurement. This could be achieved, for example, by using a mirror material that is transparent to X-rays and, when the shutter is "open", is in the beam path of the X-rays in such a way that a light beam enters the collimator bore at the same time.

-4-can be reflected .

In general, an embodiment of the invention is preferred in which, when the shutter is closed, the side of the shutter facing the collimator bore has a mirror surface that intersects the axis of the collimator bore, with a light source being arranged in the direction of the axis of the collimator bore that is mirrored in this closed position.

The shutter can, for example, consist of a prismatic block with a lower edge inclined at 45° to the collimator axis, which is inserted into the beam path from the side and thus interrupts the X-ray beam, but at the same time provides a mirror surface so that a light source arranged in the direction of the collimator axis, which in this case is mirrored at exactly 90° to the side, illuminates the mirror, which partially reflects the light through the collimator bore.

In the preferred embodiment of the invention, the closure consists of a part that can be rotated by 90° about its axis and is cylindrical in its basic shape, one surface of which runs along a plane that is angled by approximately 45° to the cylinder axis. By arranging this cylindrical part accordingly, it is possible to ensure that the X-ray beam can pass unhindered past the closure part into the collimator in the position in which the surface that runs obliquely to the cylinder axis of the closure part is essentially parallel to the axis of the collimator bore, while in a position of the closure part rotated by 90° to this, the X-ray beam is interrupted at this point, with the obliquely running cylinder surface in this case facing the collimator bore and also extending at an angle of 45° relative to this axis. This surface, which is preferably mirrored, then directs the light from a light source arranged at the level of the shutter at a distance from the collimator axis, precisely into the collimator bore and onto the object located underneath.

It is practical to couple the shutter with a switch for the corresponding light source.

In another embodiment of the invention, the collimator is tapered at its end facing the sample to be measured, so that this end can also be seen as a pointer or adjustment tip, which points precisely to the point at which the X-ray beam will hit. An embodiment of the invention is particularly preferred in which the collimator is designed to be so long that this tip is arranged directly above the sample to be measured, so that the measuring spot is clearly defined.

The collimator expediently has cylindrical symmetry, so that the tip is correspondingly conical and the bore ends exactly in the center of the slightly flattened tip. Most preferred is an embodiment of the invention in which the collimator has the shape just mentioned and in which the optical devices for guiding a light beam through the collimator bore are additionally provided.

It has proven to be useful if the bore has stepped cylindrical extensions, seen from the tip, through a relatively long collimator

In order to achieve the highest possible spatial resolution when measuring secondary radiation, the X-ray beam emerging from the collimator must be finely focused or blocked out. This requires collimator holes whose diameter is typically in the range of 0.3 to 1 mm. It goes without saying that a hole with a diameter of 0.3 mm can only be made in a very long collimator with considerable difficulty, so that the gradually expanded cylindrical hole enables considerably easier production, whereby only the last 1 to 10 mm of the end piece of the collimator must have the hole with the small diameter.

Furthermore, it has proven to be useful if, according to a further embodiment of the invention, the collimator is suspended spring-loaded from the housing of the X-ray tube or from other parts of the device, such as the shutter housing. This makes it possible to move the collimator tip against the sample without destroying it, since the collimator then retreats accordingly due to the spring-loaded suspension. Guide elements are provided which only allow the collimator to move along its bore axis, with a compression spring allowing the collimator to compress. However, this compression spring can also act as a tension spring if the collimator is moved in the opposite direction. Particularly preferred is an embodiment of the invention in which the guide elements consist of telescopically guided tube parts which are guided into one another with a precise fit and are arranged concentrically to the axis of the collimator bore, with at least one of these telescopic tube parts being surrounded by a helical spring which is supported with one end, for example, on the housing of the collimator closure and with its other end on a part rigidly connected to the collimator. A feed device can be provided which moves the entire arrangement in the direction of the sample and parallel to the collimator axis, and an additional displacement device can also be provided which moves the collimator against the action of the compression spring or with its support in the direction of the collimator axis away from or towards the sample.

A sensor is expediently provided which detects any springback of the collimator that exceeds a predetermined amount. For example, it would be possible to roughly adjust the entire device by hand or to arrange a sample on or under this device and then move the entire device with collimator or the part that holds the sample so that the tip of the collimator rests on the sample. Since the collimator is spring-mounted, it will spring back as soon as the pressure force of the tip on the sample exceeds a certain amount, with this springback being detected and registered by a sensor. Expediently, the further relative movement between the sample and the device is then stopped and the device that can move the collimator relative to the rest of the device pulls the collimator away from the sample again. Instead, however, the entire relative movement between the sample and the device could be reversed by moving in the opposite direction by an amount that slightly exceeds the amount of deflection of the collimator. In this case too, it would be ensured that the collimator tip is at a distance from the sample, with this distance preferably being in the range of 1 to 5 mm.

A practical embodiment of the invention lies in the design of a feed device in the form of a push/pull rod, which is mounted at one end on an eccentric. The eccentric can then be driven in rotation, with the push rod moving either the entire arrangement or the sample or the sample holder or even the collimator relative to the rest of the device. Stepper motors, which enable a precisely defined setting, are particularly suitable for such feed movements.

In addition, an optical and/or acoustic signal generator can be provided which indicates that the collimator tip has touched the sample.

The present invention, with its various aforementioned embodiments, the features of which can be implemented individually or in combination with one another, advantageously enables the collimator itself to be used as an adjustment element, so that a very precise adjustment of the X-ray beam can be carried out. In an embodiment that always provides a defined and very small distance between a collimator tip and the sample surface, a constant distance between the X-ray tube and the sample is also always ensured, so that a further source of error is eliminated, which is related to the different radiation intensity due to different distances between the X-ray tube and the sample. This is achieved by moving the collimator into contact with the sample, its spring suspension and the subsequent, defined retraction of the

collimator relative to the sample. As already mentioned, the only thing that matters is the relative movement of the device or the collimator to the sample, so that of course the sample itself or a holder for the sample can also be moved accordingly.

Further advantages, features and possible applications of the present invention will become clear from the following description of a preferred embodiment and the associated figures. They show:

Figure 1 shows a schematic cross section along the axis of the collimator bore through

the collimator, the collimator holder, the shutter and the adjacent housing wall of an X-ray tube,

Figure 2 the shutter in the closed position, seen from the X-ray tube

in the direction of the collimator axis,

Figure 3 the same view as in Figure 2, but with the shutter open, Figure 4 is a view corresponding to Figure 1 from behind and Figure 5 is a sectional view along the line V-V in Figure 4.

In Figure 1, the housing wall 20 of an X-ray tube (not shown) arranged above it can be seen. The housing 20 of the X-ray tube has an aperture 21 through which the X-rays can exit the housing. A shutter 5 is arranged directly under the aperture 21, with a block 23 which has a bore 24 in alignment with the aperture 21. The bore 24 ends in an essentially cylindrical space 25 which runs transversely to the axis of the bore 24. In this cylindrical space, a shutter body 26 is arranged which is cylindrical in its basic shape, but whose one end face runs at an angle of approximately 45° relative to the axis of the cylindrical part 26. Furthermore, the cylindrical part is arranged essentially concentrically in the cylindrical space 25, whereby the diameter of the part 26 is only slightly smaller than that of the cylindrical space 25 in order to fill it as much as possible and to largely avoid X-ray scattering. The cylindrical closure part 26 is linked via a shaft 27 to a rotary magnet 8, which can essentially set two different rotational positions of the shaft 27, offset by 90° from one another. As can be clearly seen in Figures 2 and 3, the closure part 7 completely covers the collimator bore 6 (and also the bore 24) in the closed position, but completely exposes them in the position rotated by 90°, which can be seen in Figure 3.

This means that in the closed position of the shutter the intersection point between

the axis 7 of the collimator bore 6 with the mirrored inclined surface of the closure part 26 is located slightly above the cylinder axis of the space 25, so that with a 45° inclination of this mirror surface relative to the collimator axis, the light source should be arranged at a distance from the collimator axis and slightly above the axis of the cylindrical closure part 26 or the cylindrical space 25, or the mirror has an inclination other than 45° relative to the collimator axis 7. In general, the condition applies that the connecting line from the light source to the point on the mirror that the axis 7 of the collimator bore intersects forms the same angle with the mirror surface 4 as the axis 7 itself, whereby the axis 7 and the said connecting line must also lie in the same plane perpendicular to the mirror plane. In other words, the mirrored axis T of the collimator bore 6 is the said connecting line from the light source to the intersection point of the axis 7 with the mirror 4.

The collimator 1 itself consists of a solid, cylindrical steel or stainless steel part with a conical, pointed front end 16. The collimator bore 6 extends along the axis of this cylindrical part and can have cylindrical extensions towards the top, i.e. away from the front end. The tip of the front end 16 is slightly flattened so that the lower bore opening is in the center of a circular area and in this area the bore has a minimum wall thickness of approx. 1 mm.

The upper end 12 of the collimator is designed in its interior as an outer tube part of a telescopic guide. On its outside, the upper end 12 of the collimator has a thread for receiving a union nut 13, which can also be replaced by a flange. A telescopic tube 11 is guided in the rear tube part 12 of the collimator 1 with the most precise fit possible and is attached with its upper end to the closure block 23 in such a way that the axis 7 of the collimator bore coincides with the axis of the aperture 21 and the bore 24. A helical compression spring 10 surrounds the telescopic tube 11 and is supported with its upper end on the closure block and with its lower end on the tube part 12 of the collimator 1. An angle 14 is provided for connection to a drive unit (not shown), which can move the collimator relative to the closure block 23 against or with the support of the force of the compression spring 10. The angle 14 has a bore that accommodates the cylindrical part of the collimator 1, which can also have a shoulder or flange for fastening the angle 14 in order to fasten the angle 14 to the collimator using the union nut 13.

In Figures 1 to 4, a light bulb 3 is shown as the light source, but this can also be replaced by a light-emitting diode or a laser. As can be seen in particular from the

As shown in Figures 3 and 4, in the case of a concentric arrangement of the light source relative to the cylinder chamber 25, the angle enclosed between the mirror surface 4 and the collimator axis 7 should be slightly larger than 45° so that the above-mentioned condition for the reflection of the light emanating from the light source 3 into the collimator bore 6 is optimally fulfilled.

In Figure 5 one can clearly see the cross-sectional shape of the closure block 23 and the cylindrical shape of the space 25, as well as the telescopic guide of the tube 11 in the upper tube part 12 of the collimator 1.

The feed and drive devices for the device and for the displacement of the collimator relative to the closure block 23 are not shown in the figures, nor are the sensor(s) for detecting the collimator deflection. However, such components and assemblies are sufficiently known in the specialist world, so that reference can be made to the known devices for such purposes.

The present invention has succeeded in permanently eliminating the problem of adjusting X-ray devices, which generate X-rays, allow them to act on a sample and measure the secondary radiation. Incorrect adjustments are practically impossible, as are subsequent misalignments, since the collimator always remains an essential element of the adjustment device and any displacement of this adjustment device would simultaneously result in a corresponding displacement or realignment of the emerging X-ray beam, so that the area indicated by the collimator is always exposed to X-rays.

At the same time, a defined distance between the preferably very thin collimator tip and the measuring area is always maintained so that the reception of secondary radiation by the collimator cannot be adversely affected.

A preferred application of such a device is the measurement of layer thickness using the X-ray fluorescence method.

-14-

Reference list I Collimator

3 Light source, incandescent lamp

4 mirror surface, mirror

5 Closure

6 Collimator hole

7 Collimator axis, shutter part T axis

8 Rotary magnet

10 helical compression spring

I1 Telescopic tube

12 rear tube part, upper collimator end, upper tube part

13 Union nut

14 angles

16 front end

20 Housing wall

21 aperture, aperture opening

23 Locking block

24 Bore

25 Cylinder chamber

26 Locking part, locking body

27 Wave

Claims (15)

-10-Protection claims 1. Device for generating and measuring the secondary radiation emitted by a sample irradiated with X-rays, comprising: an X-ray tube in a housing (20) which is substantially impermeable to X-rays, an opening (21) in the housing (20) for the exit of an X-ray beam, a collimator (1) for limiting the X-ray beam to a specific, defined area, a shutter (5) between the X-ray tube and the collimator (1), through which the X-ray beam can be interrupted, an adjustment device for aligning the collimator to determine the point of impact of the X-ray beam on a sample, and
a proportional counter tube,
characterized in that the collimator (1) forms part of the adjusting device. 2. Device according to claim 1, characterized in that a device is provided for passing a light beam through the collimator bore (6) when the shutter (5) is closed. 3. Device according to claim 2, characterized in that the device has a direct or indirect light source arranged on the closure (5). 4. Device according to claim 3, characterized in that when the shutter (5) is closed, the side of the shutter (5) facing the collimator bore (6) has a mirror surface (4) intersecting the axis (7) of the collimator bore (6) and that a light source (3) is arranged in the direction of the axis (7') of the collimator bore (6) mirrored in this closed position. 5. Device according to one of claims 2 to 4, characterized in that the shutter (5) is coupled to a switch for a light source (3). 6. Device according to one of claims 1 to 5, characterized in that the end (16) of the collimator (1) facing a sample is tapered. 7. Device according to claim 6, characterized in that the end (16) of the collimator (1) is conical, the axis (7) of the collimator bore coinciding with the cone axis of the end (16). 8. Device according to one of claims 1 to 7, characterized in that the collimator bore (6), starting from the end of the collimator (1) facing the sample, has step-shaped cylindrical extensions. 9. Device according to one of claims 1 to 8, characterized in that the collimator (1) is suspended in a spring-loaded manner in the direction of the axis (7) of its bore (6) 10. Device according to claim 9, characterized in that the resilient suspension of the collimator (1) has guide elements for a parallel displacement of the collimator (1) in the direction of its bore axis (7) and a compression spring (10) which allows a limited deflection of the collimator (1) in the direction of the shutter (5). 11. Device according to claim 10, characterized in that the guide elements are tube pieces (11, 12) arranged concentrically to the collimator axis and guided telescopically into one another, one of which is surrounded by a helical spring (10), the helical spring (10) being supported with one end against the closure (5) or a closure housing or a tube flange and with its other end against the collimator (1) or a part firmly connected to it, e.g. a second telescopic tube piece (12). 12. Device according to one of claims 9 to 11, characterized in that at least one sensor is provided which detects a springback of the collimator (1) exceeding a predetermined amount. 13. Device according to claim 12, characterized in that a device is provided by means of which the collimator (1) with the guide elements and the compression spring (10) can be moved together in the direction of an object to be measured, this device stopping the feed in response to a sensor signal as soon as the collimator has sprung back by the predetermined amount by striking an object and then moves the movable parts back by an amount exceeding the spring deflection, so that the free end of the collimator is at a distance from an object to be measured, whereby this distance is preferably 1 to 3 mm. 14. Device according to claim 13, characterized in that the device for advancing and/or retracting the collimator (1) has a push/pull rod, one end of which is mounted on an eccentric. 15. Device according to one of claims 12 to 14, characterized in that the sensor is followed by an optical and/or acoustic signal generator which indicates the springback of the collimator (1).