DE102005048519A1 - Focused aperture - Google Patents

Abstract

Around specify a focal point-oriented diaphragm (100), which in particular for high energy Radiation is provided and which a rapid displacement of the Direction of a beam which passes through a focal point, allows it is provided that an absorption element (10) is a periodic movement To run can and is shaped such that in each during the periodic movement at most a direction (18) exists with the property that radiation, In particular radiation of a certain type of jet, which on a by a focal point (16) extending beam on the focal point-oriented Aperture (100) drops, is essentially transmitted when the beam is substantially runs in said direction (18), and otherwise essentially absorbed.

Description

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

One fundamental Problem of X-ray, gamma and neutron beams is extremely small compared to visible light, virtually unusable refraction, which is the redirecting and focusing the radiation to create an optical image practically impossible makes, apart from a few cases as with bundled systems Capillaries for soft x-ray radiation. Also the deflection of this radiation by reflections is only softer Radiation possible, which also pictures with the help of mirror arrangements not come into question. To get a controllable beam with a given Strength in a desired To create direction first the suppression of all unwanted Radiation with the help of collimators done. Especially with hard radiation Minimum layer thicknesses are to be observed, which means shields and Apertures can gain a considerable weight and thus mechanically heavy become mobile. This becomes a problem especially when fast moving spot beams ("pencil beam "), for example Scanning of surfaces needed become. The inertia weighty Lets collimators only uniform Movements and only slow direction changes. Fast line by line sweeping a surface is hardly possible in this way or at least very expensive.

Is needed whereas a fast moving spot beam e.g. in the X-ray backscatter technique. Thereby an object with a wandering ray becomes point by point sampled. It is the scattered from one point scattered radiation over several, partly large area, detectors measured. The location coordinates of the measuring point are determined by the position given the collimated Strah les. By staggered line by line Moving the beam leaves Thus, a picture composed of the scattered beam intensities. Such Systems are using rigid collimator systems that have one Frame Mechanics are constantly moving, for scanning large areas, the accessible on one side are, realized.

A similar Problem arises with the site-selective spectroscopic scanning areal heterogeneous radiation sources (e.g., collection radioactive waste). In At a certain focal point, a gamma spectrometer is positioned, which using a collimator system radiation from a fixed Direction receives. If it succeeds to move this collimator system so that an area evenly line by line is scanned, then in this way the spectrum of radiation be mapped. Such an arrangement can always make sense when more spectral information is needed than the one that is needed a flat detector may optionally provide with filter attachments.

task The invention is to provide an aperture, which in particular for high energy Radiation is provided and which a rapid displacement of the Direction of a beam which passes through a focal point allows.

According to the invention this Task by means of a focus-oriented aperture with the in the claim 1 features or by a method for manufacturing 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 on a point by a running beam extending to the diaphragm is substantially transmitted when the beam is substantially in said direction and otherwise substantially absorbed. Radiation is understood here to mean radiation of a specific wavelength range (for example X-ray radiation) or else radiation which consists of specific particles (for example 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 secondly 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 restricted 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 rayar manifested by different wavelength ranges in electromagnetic waves or by the contrast of particle electromagnetic radiation.

A Acquisition of all relevant measuring points in the object to be examined or on the surface the same is made possible if at least one of the three components - focus, aperture, object - during the Periodically repeating movement of the iris either step by step or is continuously adjusted appropriately. The one selected by the aperture Direction in the practical case, of course, refers to a finite space angle range, however, it should be suitably limited to the one selected thereby View measuring range on or in the object to be examined as sufficiently punctiform to be able to.

The the simplest and most easily arranged to be realized periodic motion is a rotation about one predetermined axis of rotation. The direction vectors selected by the aperture then reproduce at least every 360 °. Also obvious are repetitions the same direction vector every 180 °, 120 °, etc. The resulting Rotary shutter can be rotated almost arbitrarily fast, limits are more likely through the registration electronics than through the mechanical axle bearings and set the drive.

In A preferred embodiment of the invention is provided that the Absorption element at least one slit-shaped gap or the radiation Having at least slightly absorbing slit-shaped area. This arises when the direction selected by the aperture at the periodic movement changes continuously.

Especially It is preferred that the directions selected by the shutter are Radiation lie on a plane, especially the plane which at a rotational movement of the diaphragm through its axis of rotation and the focal point is defined. The positions of the measuring points on the to be examined Object are thus on a line. By the above mentioned displacement one of the three arrangement elements can thereby be a conventional scanning reached the object and the creation of a raster image are 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 problem of the invention is achieved by a special method for the manufacture of the invention aperture. It comprises the following process steps:

• Provision of an absorption element made of a material suitable for the intended radiation,
• - Removal of material in the directions in which the aperture is to pass a beam through a cutting jet.

Of the Cutting beam (electromagnetic radiation or from matter), which for at least partially removing the material from the absorbent element serves, thus has the same geometric course as the beam, which is selected by the manufactured absorption element. Preference is given while the removal of the material, the absorption element at least one Period of periodic movement performed during operation of the shutter To run allow. Then the high-energy beam describes the same Change of direction like the beam selected during operation of the diaphragm.

Further it is preferred that the removal of the material by high pressure water jet cutting he follows. High pressure water jet cutting is a modern form the cutting technology, which provides a high quality 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 through a fine nozzle accelerated to a multiple of the speed of sound. If the absorption element harder Materials, so the cutting performance by the addition of Abrasives are increased.

Further preferred embodiments of the invention will become apparent from the others, in the subclaims mentioned features.

The Invention will be described below in embodiments with reference to FIG associated Drawings closer explained. Show it:

1 an arrangement with the diaphragm according to the invention,

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

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

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

1 schematically shows an arrangement with the invention, in total with 100 designated aperture. An absorption element 10 in the form of a cylinder of radiation absorbing material is rotatable about a central longitudinal axis 12 suspended. Through the absorption element 10 run one or more slots 14 , In the spotlight 16 a point-shaped beam source is positioned, which radiation of a certain wavelength range at least in the direction of the absorption element 10 sending out. The shape of the slot 14 is designed such that rays coming from the focal point 16 go out, from the absorption element 10 be absorbed, with the exception of a single beam, which in a certain selection direction 18 runs. The transmitted beam 18 falls to a certain measuring point 22 of the object to be examined 20 , The of measuring point 22 Backscattered radiation is collected by a detector, not shown.

The absorption element 10 is subject to rotation about the axis of rotation 12 , This can be carried out as a uniform movement, which can be maintained even with heavy, solid 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 changes 18 of the slot 14 transmitted beam. When rotated 180 °, this beam sweeps the surface of a fan from the focal point 16 through the axis of rotation 12 , The measuring point scanned thereby 22 on the surface of the object 20 moves on a line 24 ,

Because of the reversibility of the beam guidance, the in 1 geometry shown also applicable to the case that the object to be examined 20 itself is a source of radiation. In the spotlight 16 Then a detector is positioned, which is the object 20 emitted radiation coming from the absorption element 10 is passed through, fields and measures. Again, the absorption element selected 10 or the slot 14 the direction 18 of the transmitted beam which is focused on the detector 16 falls and, analogous to the first case of a measuring point 22 goes out, which in the rotation of the absorption element 10 around the axis of rotation 12 on a line 24 moves.

Instead of the execution of the absorption element 10 in the form of a solid cylinder, an embodiment in the form of a hollow cylinder or a pipe is also conceivable if the wall thickness ensures sufficient absorption. The choice of the 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-rays or gamma rays or polyethylene for neutron radiation.

2 shows the operation of the focus-oriented aperture in different rotational positions of the absorption element 10 , In the lower parts of the picture, the opening angle α is at the focal point 16 and above, the cylindrical absorption element 10 with the slot openings 14a and 14b shown. This is a plan view of the absorption element 10 , wherein the upwardly extending parts of the slot openings 14a , b are shown by a solid line and those on the bottom 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 defined by the opening angle α and the distance d of the focal point 16 from the axis of rotation 12 certainly. The distance of the focal point 16 facing aperture edge of aperture center is a ₁ = (d - r) tan (α / 2), when r is the radius of the cylinder is called. 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 are the progressions of the slot openings 14a , b shown on the unrolled cylinder shell as a phase diagram. This is the different length of the slot openings 14a , b especially 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 as an arrow in the upper partial images and thus indicates entry and exit position on the cylinder surface. The in the 2 marked arrow directions, which the transmitted beam 18 represent, have an orientation which one in focus 16 positioned beam source corresponds. Because of the reversibility of the beam guidance, these arrows could also run in exactly the opposite direction when the object to be examined 20 itself beam source is in focus 16 a detector is positioned.

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

1. First edge position ( 2a ):

A ray 18 passes through the absorption element unhindered in the maximum opening angle 10 from the end of the shorter gun side slot opening 14a to the corresponding end of the longer, Strahlerabgewandten slot opening 14b , All other rays are caused by the twisting of the aperture slot 14 or by the radiation-absorbing matter in the absorption element 10 absorbed.

2. First zero position ( 2 B ):

After a rotation of 90 ° with respect to the first edge position, the transmitted beam passes 18 exactly perpendicular to the axis of rotation 12 through the slot 14 , In the positions between the first edge position and the zero position passes through the beam 18 continuously all angles between α / 2 and 0 (angle measured between beam direction 18 and the solder from the focal point 16 on the axis of rotation 12 ). For each of these transmitted rays 18 Only one almost punctiform passage opening from the slot 14 Approved.

3. Second edge position ( 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 the absorption element 10 at the opposite end passes through the angle α / 2. Overall, the directions of the transmitted rays are 18 during the rotation of the aperture 100 on a fan with the opening angle α. The transmitted beam accordingly scans 18 a line 24 of measuring points 22 on the object to be examined 20 from.

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

The one of the two borderlines between top 26 and bottom 28 (marked by the arrows 30 ) corresponds to the generatrix on the cylinder 10 which the focal point 16 is closest and through which the selected beam 16 runs.

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

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

During the above-described rotation positions following half rotation of the cylinder 10 does not become a beam direction 18 with the exception of the second zero position (after a 90 ° turn to position 3 (see above), in which the central ray (parallel to the perpendicular of the focal point 16 on the axis of rotation 12 ) is allowed through. Thus, each ray passes through the center of the cylinder 10 a phase shift of 180 ° between inlet and outlet on the surface of the cylinder 10 ,

3 represents the integration of the absorption element 10 in an arrangement with shielding elements 32 (view from above). In the case shown, the absorption element 10 of two shields 32 flanked by hollow cylindrical faces in which it can rotate freely. Mechanical is the absorption element 10 so store it around the central axis 12 is freely rotatable. A controlled drive 34 is to be mounted so that it is at the upper or lower extension of the axis of rotation 12 engages 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 stepping motor with precise step counting or a position control on the cylinder 10 itself. The drive unit 34 can both in the shield 32 integrated or attached to the side facing away from the radiation. High demands are placed on the mechanics because of the exact angular position control (direct gear or chain transmission).

Every second central beam through the aperture 100 is in a preferred embodiment switching technology 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 about the same state of the rotating cylinder 10 communicated to the registering system. 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, causing on the object to be examined 20 a line 24 is scanned. For the registration of areas is in the in 3 illustrated embodiment provided that the focal point 16 on a fixed radius around the axis of rotation 12 as far as it is guided as the shielding device 32 allows. In this case, the shielding device needs 32 not 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 by the fact 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 panel 100 at the object 20 is passed. In addition, there is the possibility of the absorption element 10 on a circular arc around the focal point 16 to move.

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 one in focus 16 radiation source does not emit (predominantly) homogeneous radiation, which can be screened with 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 from a first, for a first radiation type absorbing material M1 on, for example, a heavy metal, which is suitable for shielding X-rays and gamma rays. The cylindrical core area 40 consists of a second material M2 absorbing for a second radiation type, eg a hydrogen-rich material such as polyethylene or a light element such as boron for neutron absorption.

Also the shielding element 32 must effectively shield all types of radiation used, resulting in a shell-shaped construction with the use of the two materials M1 and M2 ( 32a , b) is accomplished.

For better evaluation of the measured signals are 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.

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 the generatrix on the cylinder

32

absorbing element

32a, b

absorbing elements made of different absorbent materials

34

drive

36

position control

38

coat of the absorption element

40

core of the absorption element

100

cover

Claims (14)

Focus-oriented aperture ( 100 ) with an absorption element ( 10 ), characterized in that the absorption element ( 10 ) can perform a periodic movement and is shaped such that in each position taken during the periodic movement at most one direction ( 18 ) exists with the property that radiation, in particular radiation of a certain type of radiation, which is focused on one by one focal point ( 16 ), extending beam on the focus-oriented aperture ( 100 ) is substantially transmitted when the beam is substantially in said direction ( 18 ), and otherwise substantially absorbed. Focus-oriented aperture ( 100 ) according to claim 1, characterized in that the of the absorption element ( 10 ) executable periodic movement a rotational movement about an axis of rotation ( 12 ). Focus-oriented aperture ( 100 ) according to one of the preceding claims, characterized in that the absorption element ( 10 ) has a cylindrical shape. Focus-oriented aperture ( 100 ) according to one of the preceding claims, characterized in that the absorption element ( 10 ) at least one slot-shaped gap ( 14 ) or a radiation absorbing at least slightly slit-shaped area. Focus-oriented aperture ( 100 ) according to one of claims 2 to 4, characterized in that said directions ( 18 ) lie on a plane, in particular the plane which passes through the axis of rotation ( 12 ) and the focal point ( 16 ) is defined. Focus-oriented aperture ( 100 ) according to one of claims 3 to 5, characterized in that the cylinder different materials in the core ( 40 ) and in the jacket area ( 38 ), which absorb different types of rays differently. Focus-oriented aperture ( 100 ) according to one of claims 1 to 5, characterized in that the absorption element ( 10 ) has the shape of a hollow cylinder or tube. Focus-oriented aperture ( 100 ) according to one of the preceding claims, characterized in that in focus ( 16 ) A detector is provided. Focus-oriented aperture ( 100 ) according to one of the preceding claims, characterized in that in focus ( 16 ) A radiation source is provided. Focus-oriented aperture ( 100 ) according to one of claims 2 to 9, characterized in that the focal point ( 16 ) can be guided in a circular movement about the axis of rotation as the center. Focus-oriented aperture ( 100 ) according to one of the preceding claims, characterized in that the absorption element ( 10 ) of stationary, the radiation absorbing shields is surrounded. Method for producing a focal point-oriented diaphragm ( 100 ) according to one of the preceding claims, characterized by the following method steps: - provision of an absorption element ( 10 ) of a material suitable for the intended radiation, - removal of material in the directions in which the focal point-oriented diaphragm ( 100 ) is to pass a beam through a cutting jet. Method according to claim 12, characterized in that that the removal of the material by high-pressure water jet cutting he follows. Method according to one of claims 12 and 13, characterized in that the absorption element ( 10 ) performs at least one period of said periodic movement during removal of the material.