EP1772874B1 - Focal point oriented aperture - Google Patents

Abstract

A focus orientating aperture for a high energy radiation beam from a source (16) comprises, an absorption cylinder (10) capable of periodic motion, e.g. axial rotation, and provided with one or more apertures (14), such that all radiation incident on the cylinder surface is absorbed, but a uni-directional ray (18) along the axis of the aperture is transmitted to an investigated sample or work surface. an INDEPENDENT CLAIM is included for a method of manufacturing a perforated absorption cylinder, particularly by the use of a high pressure (approx.3800 bar) water cutting jet. Dependent on the application, the absorption cylinder may comprise e.g. a cylindrical outer sheath of copper, tungsten, or heavy metal, with an inner core of polyethylene or boron. The collimation device can be used in the reverse sense to handle radiation scattered from a surface, with a detection element positioned at the focal point (16).

Description

The invention relates to a focal point-oriented diaphragm according to the preamble of claim 1 and a method for producing the same according to the preamble of claim 12.

A fundamental problem of X-ray, gamma and neutron beams is the extremely low, practically unusable refraction compared to visible light, which makes it virtually impossible to redirect and focus the radiation to produce an optical image, except in a few cases such as in systems with bundled capillaries for soft X-rays. Also, the deflection of this radiation by reflections is only possible with soft radiation, which also images by means of mirror arrangements are out of the question. In order to produce a controllable beam with a given strength in a desired direction, the suppression of all unwanted radiation must first be effected with the aid of collimators. Minimum layer thicknesses must be taken into account, especially with hard radiation, as a result of which shields and diaphragms can acquire considerable weight and thus become mechanically difficult to move. This becomes a problem especially when fast moving pencil beams, e.g. needed for scanning surfaces. The mass inertia of weighty collimators allows only uniform movements and only slow changes of direction. Fast line by line sweeping a surface is hardly possible in this way or at least very expensive.

What is needed, however, is a fast-moving spot beam, for example in X-ray backscatter technology. An object is scanned point by point with a wandering beam. It is the backscattered scattered radiation from a point over several, sometimes large area, detectors measured. The location coordinates of the measuring point are given by the position of the collimated beam. By staggered line by line movement of the beam can thus be an image from the scattered beam intensities put together. Such systems are realized with rigid collimator systems that are steadily advanced via frame mechanics for scanning large areas that are unilaterally accessible.

A similar problem arises with the site-selective spectroscopic scanning of areal heterogeneous radiation sources (e.g., collection bin for radioactive waste). At a certain focal point, a gamma spectrometer is positioned which receives radiation from a predetermined direction by means of a collimator system. If it is possible to move this collimator system so that a surface is scanned uniformly line by line, then the spectrum of a radiation can be mapped in this way. Such an arrangement can always make sense if more spectral information is required than that which a flat detector can optionally provide with filter attachments.

The object of the invention is to provide a diaphragm, which is provided in particular for high-energy radiation and which allows a rapid displacement of the direction of a beam which passes through a focal point.

According to the invention this object is achieved by means of a focus-oriented aperture with the features mentioned in claim 1 or by means of a method for producing the same with the features mentioned in claim 12.

The absorption element can perform a periodic movement and is shaped such that in each position taken during the periodic movement at most one direction exists with the property that radiation, in particular radiation of a particular type of radiation, which falls on a beam passing through a focal point on the diaphragm , is substantially transmitted when the beam is substantially in said direction and otherwise substantially absorbed. By radiation type here is radiation of a certain Wavelength range understood (eg X-ray) or radiation, which consists of certain particles (eg neutron radiation). Such a focal point-oriented diaphragm is suitable for two general optical arrangements, firstly an arrangement in which a beam source is positioned at the focal point and a beam is guided by means of the diaphragm over an object to be examined, whose scattered radiation is then measured by a detector, or secondarily Arrangement in which the object to be examined itself produces radiation and the diaphragm serves to direct the radiation of a specific point of the object onto a detector in focus. The selection property of the diaphragm with respect to the beam direction can, on the one hand, relate to radiation of all kinds (regardless of wavelengths and / or particle nature) or, on the other hand, be limited to a specific type of radiation. In particular, it is possible that the diaphragm simultaneously transmits radiation of a first type of radiation (for example X-radiation) in a first direction and radiation of a second type of radiation (for example neutron radiation) in a second direction. As mentioned above, the different types of radiation can be manifested by different wavelength ranges in electromagnetic waves or by the contrast of particle-electromagnetic radiation.

A detection of all relevant measurement points in the object to be examined or on the surface of the same is made possible if at least one of the three components - focus, aperture, object - during the periodically repeating movement of the diaphragm is offset either stepwise or continuously appropriate. In the practical case, the direction selected by the diaphragm naturally refers to a finite solid angle range, which, however, should be suitably limited in order to be able to regard the thus selected measuring range on or in the object to be examined as sufficiently punctiform.

The simplest and according to the order of the easiest to realize periodic movement is a rotational movement about a predetermined axis of rotation. The direction vectors selected by the diaphragm then reproduce at least every 360 °. Also obvious are repetitions of the same direction vector every 180 °, 120 °, etc. The resulting rotating aperture can be rotated almost as fast as desired, limits are set by the registration electronics rather than by the mechanical axis bearing and the drive.

In a preferred embodiment of the invention, it is provided that the absorption element has at least one slit-shaped gap or a slit-shaped region which absorbs the radiation at least to a small extent. This occurs when the direction selected by the shutter changes continuously during the periodic movement.

In particular, it is preferred that the directions of the radiation selected by the diaphragm lie on a plane, in particular the plane which is defined during a rotational movement of the diaphragm through its axis of rotation and the focal point. The positions of the measuring points on the object to be examined are thus on one line. By the above-mentioned displacement of one of the three arrangement elements thereby a conventional scanning of the object can be achieved and the creation of a raster image can be made possible.

• Bereitstellung eines Absorptionselements aus einem für die vorgesehene Strahlung geeignet absorbierenden Material,
• Entfernung von Material in den Richtungen, in welcher die Blende einen Strahl durchlassen soll, durch einen Schneidstrahl.

The panel according to the invention can be produced by a conventional milling method. In addition, the technical object of the invention is achieved by a special method for producing the diaphragm according to the invention. It comprises the following process steps:

• Providing an absorbent element of material suitable for the intended radiation,
• Removal of material in the directions in which the aperture is to transmit a beam through a cutting jet.

The cutting beam (electromagnetic radiation or of matter), which serves for the at least partial removal of the material from the absorption element, thus has the same geometric course as the beam which is selected by the manufactured absorption element. It is preferred, during the removal of the material, to let the absorption element carry out at least one period of the periodic movement performed during operation of the diaphragm. Then the high-energy beam describes the same direction changes as the beam selected during operation of the diaphragm.

It is further preferred that the removal of the material takes place by high pressure water jet cutting. High-pressure water jet cutting is a modern form of cutting technology that delivers a high quality of cut. Fresh water is strongly compressed by a special high-pressure pump, so that a cutting pressure of about 3800 bar can be achieved, and then accelerated through a fine nozzle to a multiple of the speed of sound. If the absorption element consists of harder materials, the cutting performance can be increased by the addition of abrasives.

Further preferred embodiments of the invention will become apparent from the remaining, mentioned in the dependent claims characteristics.

Figur 1

eine Anordnung mit der erfindungsgemäßen Blende,

Figur 2

Funktionsweise der fokal ausgerichteten Blende in drei verschiedenen Drehpositionen,

Figur 3

die Integration der erfindungsgemäßen Blende in eine Gesamtabschirmung und

Figur 4

die erfindungsgemäße Blende mit Abschirmung durch zwei verschiedene Materialien.

The invention will be explained in more detail in embodiments with reference to the accompanying drawings. Show it:

FIG. 1

an arrangement with the diaphragm according to the invention,

FIG. 2

Operation of the focal-aligned aperture in three different rotational positions,

FIG. 3

the integration of the diaphragm according to the invention in an overall shield and

FIG. 4

the panel according to the invention with shielding by two different materials.

FIG. 1 schematically shows an arrangement with the invention, generally designated 100 aperture. An absorption element 10 in the form of a cylinder of radiation-absorbing material is rotatably suspended about a central longitudinal axis 12. Through the absorption element 10, one or more slits 14 extend. In the focal point 16, a point-shaped radiation source is positioned, which emits radiation of a specific wavelength range at least in the direction of the absorption element 10. The shape of the slit 14 is designed so that rays emanating from the focal point 16 are absorbed by the absorption element 10, with the exception of a single beam, which runs in a specific selection direction 18. The transmitted beam 18 falls on a specific measuring point 22 of the object 20 to be examined. The radiation backscattered by measuring point 22 is picked up by a detector (not shown).

The absorption element 10 is subject to a rotation about the axis of rotation 12. This can be carried out as a uniform movement, which can be maintained even with heavy, massive design using a low-friction axle bearing without great effort. Only the start-up phase requires more energy due to the necessary acceleration. During the rotation of the absorption element 10, the selection direction 18 of the beam transmitted through the slot 14 changes. When rotated through 180 °, this beam passes over the surface of a fan from the focal point 16 through the axis of rotation 12. The measuring point 22 thus scanned on the surface of the object 20 moves on a line 24.

Because of the reversibility of the beam guidance, the in FIG. 1 shown geometry also applicable to the case that the object to be examined 20 itself is a radiation source. At the focal point 16, a detector is then positioned, which captures and measures the radiation emitted by the object 20, which is transmitted by the absorption element 10. Here, too, the absorption element 10 or the slot 14 selects the direction 18 of the transmitted beam, which falls on the detector at the focal point 16 and, analogous to the first case, starts from a measuring point 22 which rotates about the axis of rotation 12 during the rotation of the absorption element 10 a line 24 moves.

Instead of the embodiment of the absorption element 10 in the form of a solid cylinder and a non-inventive embodiment in the form of a hollow cylinder or a pipe is conceivable if the wall thickness ensures sufficient absorption. The choice of material of the absorption element 10 depends on the nature of the radiation to be shielded, heavy metals such as copper or tungsten for hard X-ray or gamma radiation or polyethylene for neutron radiation.

FIG. 2 shows the operation of the focus-oriented aperture in different rotational positions of the absorption element 10. In the lower parts of the image, the opening angle α is shown with the focal point 16 and above the cylindrical absorption element 10 with the slot openings 14a and 14b. This is a plan view of the absorption element 10, wherein the top-running parts of the slot openings 14a, b are shown by a solid line and the underside by a dashed line. The two slot openings 14a, b have a different length due to the finite angle α. The exact dimensions of the slot openings 14a, b are determined by the opening angle α and the distance d of the focal point 16 from the axis of rotation 12. The distance of the focal point 16 facing the opening edge of aperture center is a ₁ = (dr) tan (α / 2), if where r is the radius of the cylinder. The one on the opposite side is analogous to a ₂ = (d + r) tan (α / 2). The rotational positions shown in the partial images of the figure are displayed in the schematic inserts bottom left by the arrow directions. The partial images a to c thus represent different rotational positions. In the upper partial images, the courses of the slot openings 14a, b on the unrolled cylinder jacket are shown as a phase diagram. Therein, the different length of the slot openings 14a, b is particularly clear. Shown are also the top 26 and the bottom 28 of the cylinder 10. The in the respective rotational position of the aperture 100 transmitted beam 18 is marked in the upper partial images as an arrow and thus indicates entry and exit position on the cylinder surface. The in the FIG. 2 marked arrow directions, which represent the transmitted beam 18, have an orientation which corresponds to a positioned in the focal point 16 beam source. Because of the reversibility of the beam guidance, these arrows could also run in exactly the opposite direction if the object 20 to be examined itself is a beam source and a detector is positioned at the focal point 16.

1. 1. Erste Randstellung (Figur 2a):
   • Ein Strahl 18 durchläuft im maximalen Öffnungswinkel ungehindert das Absorptionselement 10 vom Ende der kürzeren strahlerseitigen Schlitzöffnung 14a zum entsprechenden Ende der längeren, strahlerabgewandten Schlitzöffnung 14b. Alle anderen Strahlen werden durch die Verdrehung des Blendenschlitzes 14 bzw. durch die strahlenabsorbierende Materie im Absorptionselement 10 absorbiert.
2. 2. Erste Nullstellung (Figur 2b):
   • Nach einer Drehung um 90° bezüglich der ersten Randstellung tritt der durchgelassene Strahl 18 genau senkrecht zur Drehachse 12 durch den Schlitz 14. In den Positionen zwischen der ersten Randstellung und der Nullstellung durchläuft der Strahl 18 kontinuierlich alle Winkel zwischen α/2 und 0 (Winkel gemessen zwischen Strahlrichtung 18 und dem Lot vom Brennpunkt 16 auf die Drehachse 12). Für jeden dieser durchgelassenen Strahlen 18 wird immer nur eine nahezu punktförmige Durchtrittsöffnung vom Schlitz 14 freigegeben.
3. 3. Zweite Randstellung (Figur 2c) :
   • Zwischen Nullstellung und zweiter Randstellung wiederholt sich spiegelverkehrt der gleiche Verlauf wie zwischen der ersten Randstellung und der Nullstellung, bis der durchgelassene Strahl 18 das Absorptionselement 10 am entgegengesetzten Ende unter dem Winkel α/2 durchläuft. Insgesamt liegen die Richtungen der durchgelassenen Strahlen 18 während der Drehung der Blende 100 auf einem Fächer mit dem Öffnungswinkel α. Entsprechend tastet der durchgelassene Strahl 18 eine Zeile 24 von Messpunkten 22 auf dem zu untersuchenden Objekt 20 ab.

In turn, the focus-oriented aperture 100 passes through the following stations:

1. 1. First edge position ( FIG. 2a ):
   • A beam 18 passes through the absorption element 10 at the maximum opening angle unhindered from the end of the shorter projector-side slot opening 14a to the corresponding end of the longer, beam-facing slot opening 14b. All other beams are absorbed by the rotation of the diaphragm slot 14 or by the radiation-absorbing material in the absorption element 10.
2. 2. First zero position ( FIG. 2b ):
   • After rotation through 90 ° with respect to the first edge position, the transmitted beam 18 passes through the slot 14 exactly perpendicular to the axis of rotation 12. In the positions between the first edge position and the zero position, the beam 18 continuously traverses all angles between α / 2 and 0 (angle measured between the beam direction 18 and the solder from the focal point 16 to the axis of rotation 12). For each of these transmitted beams 18 only one almost punctiform passage opening is released from the slot 14.
3. 3. Second edge position ( Figure 2c ):
   • Between zero position and second edge position is mirrored the same course repeated as between the first edge position and the zero position until the transmitted beam 18 passes through the absorption element 10 at the opposite end at the angle α / 2. Overall, the directions of the transmitted rays 18 are during the rotation of the diaphragm 100 on a fan with the opening angle α. Accordingly, the transmitted beam 18 scans a line 24 of measuring points 22 on the object 20 to be examined.

Not shown is the second zero position after another rotation by 90 °. For symmetry reasons, the central beam is transmitted as in the first zero position.

One of the two boundary lines between top 26 and bottom 28 (marked by the arrows 30) corresponds to the surface line on the cylinder 10, which is closest to the focal point 16 and through which the selected beam 16 passes.

When the three stages described are summarized, it follows that the movement of the transmitted beam 18 via a line 24 by a half turn of the cylinder 10 takes place.

In a slow rotational movement, it is conceivable, the cylinder 10 after a half turn for the next line 24 back to turn back, so as to pass through the next line 24 in the opposite direction. Mechanically cheaper, however, it is to leave the cylinder in a constant rotational movement.

During the half rotation of the cylinder 10 following the above-described rotational positions no beam direction 18 is selected, with the exception of the second zero position (after a rotation of 90 ° to position 3 (see above)), in which the central beam (parallel to the solder of the focal point 16) the axis of rotation 12) is allowed to pass. Thus, each beam passage through the center of the cylinder 10 corresponds to a phase shift of 180 ° between the entrance and exit points on the surface of the cylinder 10.

FIG. 3 represents the integration of the absorption element 10 in an array with shielding 32 (view from above). In the case shown, the absorption element 10 is flanked by two shields 32 with hollow cylindrical end faces, in which it can rotate freely. Mechanically, the absorption element 10 is to be stored so that it is freely rotatable about the central axis 12. A controlled drive 34 is to be mounted so that it engages the upper or lower extension of the rotation axis 12, without any part of it can protrude into the beam path. A precise position control 36 communicates with the data acquisition, not shown. Suitable for this purpose is a stepper motor with precise step counting or a position control on the cylinder 10 itself. The drive unit 34 can be integrated into the shield 32 or attached to the side facing away from the radiation. To the mechanics are high requirements because of the exact angular position control to put (direct gear or chain transmission).

Each second centrally extending beam through the aperture 100 is in a preferred embodiment switching technically or mechanically with a synchronized further, not shown aperture (in wing design o. Ä.) Hidden. This can be accomplished by turning off the emitter in the second half of each rotational movement, when short switching times are possible, or mute the receiver electronics. Should both be difficult or impossible, the rotation can be coupled to an unillustrated shutter which closes the beam path during the second half turn. As long as an electronic hiding the second half-rotation is possible, this is the preferred solution, whereby short sampling times are possible with fast rotational movement. The respective position of the measuring point 22 is communicated to the registering system via the simultaneous state of the rotating cylinder 10. This can be done via a stepper motor or a stroboscope device on the upper or lower edge of the cylinder.

The result of a usable half-turn of the cylinder 10 is thus the sweeping of the transmitted beam 18 over a fan, whereby a line 24 is scanned on the object 20 to be examined. For the registration of areas is in the in FIG. 3 illustrated embodiment, that the focal point 16 is guided on a fixed radius about the axis of rotation 12 as far as it allows the shielding device 32. In this case, the shielding device 32 itself does not need to be moved.

In further embodiments, not shown, the displacement of the measuring line 24 on the object 20 in a direction perpendicular to the axis of rotation 12 achieved in that the object 20 on a stationary structure of the aperture 100 (eg on a conveyor belt) or vice versa a mobile device with the Aperture 100 is guided past the object 20. In addition, it is possible to move the absorption element 10 on a circular arc around the focal point 16.

FIG. 4 shows an arrangement in which the absorption element has different absorption materials which are effective for different types of radiation. The use of such an arrangement lends itself when the object 20 or a radiation source located in the focal point 16 does not (predominantly) emit homogeneous radiation, which can be shielded with one and the same material (example: isotope source with different types of radiation such as ²⁵² Ca). The absorption element 10 has a hollow cylindrical shell 38 made of a first, for a first radiation type absorbing material M1, for example a heavy metal, which is suitable for shielding X-rays and gamma rays. The cylindrical core portion 40 is composed of a second material M2 absorbing for a second radiation type, for example a hydrogen-rich material such as polyethylene or a light element such as boron for neutron absorption.

Also, the shielding member 32 must shield all the types of radiation used effectively, which is accomplished by a bowl-shaped structure with the use of the two materials M1 and M2 (32 a, b).

For better evaluation of the measured signals, the passage slots 14 in the cylinder parts 38 and 40, which are each effective for a beam type, offset from each other, for example, at an angle of 90 ° about the axis of rotation. Thus, more than one beam passes through the absorption element for a certain period of the rotation period, but only at most one for each particular type of radiation.

LIST OF REFERENCE NUMBERS

10

absorbing element

12

axis of rotation

14

slot

14a, b

slot openings

16

focus

18

Selection direction / transmitted beam

20

object

22

measuring point

24

measuring line

26

Top of the cylinder

28

Bottom of the cylinder

30

Position of the generatrix on the cylinder

32

absorbing element

32a, b

Absorbent elements of different absorbent materials

34

drive

36

position control

38

Sheath of the absorption element

40

Core of the absorption element

100

cover

Claims (12)

1. A focal point-oriented aperture (100) with an absorption element (10), wherein said absorption element (10) is capable of executing a periodic movement, and is formed in such a manner that in each position adopted during the periodic movement, a maximum of one direction (18) exists with the property that radiation, in particular radiation of a particular type of beam, which falls on a beam which runs through a focal point (16) onto the focal point oriented aperture (100) is essentially allowed through when the beam runs essentially in the said direction (18), and is otherwise essentially absorbed, characterized in that the absorption element (10) comprises the form of a solid cylinder.
2. A focal point-oriented aperture according to claim 1, characterized in that the periodic movement which can be executed by the absorption element (10) is a rotational movement around a rotational axis (12).
3. A focal point-oriented aperture according to any one of the preceding claims, characterized in that the absorption element (10) comprises at least one slit-shaped gap (14) or a slit-shaped area which is at least slightly absorbent.
4. A focal point-oriented aperture according to either of claims 2 or 3, characterized in that the said directions (18) lie on one plane, in particular, the plane which is defined by the rotational axis (12) and the focal point (16).
5. A focal point-oriented aperture according to any one of the preceding claims, characterized in that the cylinder comprises different materials in its core (40), and in the mantle area (38), which absorb different types of beam in a different manner.
6. A focal point-oriented aperture according to any one of the preceding claims, characterized in that a detector is provided in the focal point (16).
7. A focal point-oriented aperture according to any one of the preceding claims, characterized in that a beam source is provided in the focal point (16).
8. A focal point-oriented aperture according to any one of claims 2 to 7, characterized in that the focal point (16) can be moved in a circular movement around the rotational axis as the centre point.
9. A focal point-oriented aperture according to any one of the preceding claims, characterized in that the absorption element (10) is surrounded by stationary shields which absorb the radiation.
10. A method for producing a focal point-oriented aperture (100) according to any one of the preceding claims, characterized by the following process stages:

    - preparation of an absorption element (10) from a material which is suitable for absorbing the intended radiation,

    - removal of material in the directions in which the focal point-oriented aperture (100) is designed to allow a beam through by means of a cutting beam.
11. A method according to claim 10, characterized in that the removal of the material is achieved using high-pressure water jet cutting.
12. A method according to either of claims 10 or 11, characterized in that the absorption element (10) executes at least one period of the said periodic movement while the material is being removed.

Images