DE102005029674A1 - Aperture for an imaging device - Google Patents

Abstract

The invention relates to a diaphragm (100), in particular for an imaging device (200), which is suitable for limiting radiation (12) emanating from a radiation source (10), in particular high-energy radiation, and along an optical axis x for a hole camera principle Aiming portion (14) to be directed, characterized in that the diaphragm (100) DOLLAR A - a first radiation (12) at least partially absorbing body (18) having a first curved outer surface (20), the surface contour at least partially by a Function of the form z (x, y) = f (y) È x + n, DOLLAR A and DOLLAR A - a second body (26) at least partially absorbing the radiation (12), which has a second curved outer surface (28 ) whose surface contour is formed at least partially complementary to the curved outer surface (20) of the first absorbent body (18). DOLLAR A It is envisaged that the two absorbent bodies (18, 26) are positioned or positioned such that between the two curved outer surfaces (20, 28) there is a gap (32) or a low-absorbing radiation area.

Description

The The invention relates to a diaphragm, in particular for an imaging device, according to the generic term of claim 1.

Frequently poses the problem, the form of hidden sources of higher energy Radiation with unknown structure or spatial structure to investigate. The radiation source may be, for example around the effective focal spot on the anode of an x-ray tube or around flat act distributed radiating material. The latter can be over one Space distributed radioactive waste be in a collecting bin, with supposed discrepancies between Declaration and actual Clarify content are. Further examples of Radiation sources whose shape one wants to image are deposits with uranium ores or nuclear installations, which are often not only of concern is to determine the nature of the radiation, but also the spatial Determine the structure of the radiation sources. Besides the mentioned sources, which generate the high energy radiation directly, too to name such, which these by X-ray or Gammarückstreuung produce.

Around to depict the shape of such radiation sources, it is obvious to apply the principle of a camera. It can be quite different area detectors be used: film material, storage disks, storage foils, Semiconductor flat panel detectors, vidicams, image intensifiers or converter foils. Since such recordings can also and especially occur in environments in which, if possible Persons should not enter, one must if possible easy operability to be ensured. The simplest functionality and handling would be a remote-controlled placement of a corresponding device with a return to the exposure time without any operation of any controls.

It is known when imaging with the help of high-energy radiation to use the Lochkameraprinzip. In a pinhole camera or camera obscura creates a small hole on a projection screen Image of illuminated or radiating objects. there limited the small diameter of the aperture on the incident beam a small opening angle and thus prevents the complete overlap the rays in the image area. Rays fall from an upper area of a radiating body on the lower edge of the screen, while reversed rays from the lower area on the upper edge of the projection screen become. Thus, every point of the item is considered as a sliver on the projection imaged, so the overlay the slices provide an image of the radiant body, the resolution of the Distance of the radiating body and the shape of the aperture depends.

at high-energy radiation, the problem occurs because of their high permeability the thickness of the material for the pinhole big, this means in relation to to the half-value thickness of the intensity the radiation used for imaging must be selected. That's why the achievable image quality essentially determined by aperture diameter and material thickness and density. Often receives one therefore at best a silhouette of the actual pinhole, where the pinhole to be used for mapping, due to the wall thickness becomes a collimator, passing only a straight-line beam leaves. Therefore, often the aperture in the hole cameras with trumpet-shaped the narrow spot to the radiation source designed around the imaging Properties not completely lose.

The DE 690 01 117 discloses a device for detecting radiation sources in real time. The device comprises a collimator which is delimited by a wall in the form of a double cone, the double cone being formed from two cones of the same opening angle, which are set opposite each other at the vertex. The vertex forms the pinhole of the resulting camera.

To increase the opening angle of a pinhole camera for high-energy radiation while maintaining a high resolution, suggests the DD 240 091 a rotating diaphragm system, which consists of several concentrically arranged around the optical axis hollow cones. Each hollow cone consists of half of the respective radiation strongly or weakly absorbing material, the hollow halves are inserted into each other so that always hollow cone halves of different materials adjoin one another.

Another mechanically moving solution is from the DE 40 00 507 known, in which a slit aperture acts like the opening of a pinhole camera. The relative movement of the slit diaphragm to the detector exposes the radiation scattered from various points of the test object to the detector. Due to the relative position of the slit, it is predetermined from which depth of the test object secondary radiation is detected by a detector.

A solution for expanding the field of view in a pinhole camera is from the DE 196 03 212 in which the core of the camera has a cylindrical borehole crystal, which is closed off by a pinhole collimator, which in the region of the borehole is conical is arched. In the center of the collimator is an aperture. Depending on the shape of the collimator, the field of view has an opening angle of up to approximately 120 °.

In addition, various approaches are known from the prior art to solve the problem of penetration of hard radiation for a diaphragm with the lowest possible layer thickness. For example, near-surface collimators are to be mentioned with. Inclined plates, which from the US 6,377,661 known or the use of moving collimators ( GB 1 046 337 ).

disadvantage all described solutions is that due to the required high energy radiation Material thickness a significant deviation from the ideal Lochkameraprinzip present, except when mechanically moving solutions are used, which are very expensive.

task the invention is to provide a diaphragm for a pinhole camera, which is not based on a mechanically agitated solution and which is can realize thickness with almost any material layer, without while losing their imaging properties.

According to the invention Task by means of a diaphragm, in particular for an imaging device, solved with the features mentioned in claim 1.

• – einen ersten die Strahlung wenigstens teilweise absorbierenden Körper, welcher eine erste geschwungene Außenfläche aufweist, deren Oberflächenkontur zumindest teilweise durch eine Funktion der Form z(x, y)= f(y)·x + n (n = const.) beschrieben werden kann,

und

• – einen zweiten die Strahlung wenigstens teilweise absorbierenden Körper, welcher eine zweite geschwungene Außenfläche aufweist, deren Oberflächenkontur zumindest teilweise komplementär zu der geschwungenen Außenfläche des ersten absorbierenden Körpers geformt ist,

umfasst,
wobei die beiden absorbierenden Körper derart positioniert oder positionierbar sind, dass zwischen den beiden geschwungenen Außenflächen ein Spalt oder zumindest ein die Strahlung gering absorbierender Bereich vorhanden ist, lässt sich eine Lochkamera in nahezu beliebiger Schichtdicke nachahmen, welche völlig ohne mechanisch bewegte Teile auskommt. Die Einschränkungen gegenüber dem idealen Lochkameraprinzip sind hierbei gering. Der die Strahlung gering absorbierende Bereich kann mit einem geeigneten Material gefüllt sein, welches die relevante Strahlung weniger absorbiert als die beiden Körper, welche die Blende umfasst, wobei das Material in Form eines sepa raten Einsatzstückes oder einer auf mindestens eine der Außenflächen aufgebrachte Beschichtung vorliegen kann. Im folgenden soll unter einem Spalt auch ein solcher die Strahlung gering absorbierender und mit Material gefüllter Bereich verstanden werden. Für die Beschreibung der Oberflächenkontur wird ein dreidimensionales kartesisches Koordinatensystem zugrunde gelegt, dessen Ursprung ohne Beschränkung der Allgemeinheit auf der ersten geschwungenen Außenfläche liegt (vergleiche 2a). Die Funktionsweise der Blende lässt sich dadurch erläutern, dass ein Strahlbündel mit einem Richtungsvektor (1, y_s, z_s) betrachtet wird, also ein Strahlenbündel, welches sich in der Richtung der positiven optischen Achse x fortpflanzt. Für diejenigen Strahlenbündel, deren y-Komponente verschwindet und die sich durch einen Richtungsvektor (1, 0, tan α) beschreiben lassen (vergleiche 2b), existiert eine Gerade auf der ersten geschwungenen Außenfläche, welche parallel zum Strahlenbündel verläuft, wenn f(y) = tan α gilt. Wenn f(y) eine monoton steigende oder fallende Funktion ist, ist somit nur an einer Stelle eine Durchsicht durch den entstehenden Spalt in gerader Richtung möglich. An anderen Stellen wird die Strahlung stärker absorbiert.Because of the aperture

• A first body at least partially absorbing the body, which has a first curved outer surface whose surface contour can be described at least partially by a function of the form z (x, y) = f (y) x + n (n = const.) .

and

• A second body at least partially absorbing the body having a second curved outer surface whose surface contour is formed at least partially complementary to the curved outer surface of the first absorbent body,

includes,
wherein the two absorbent bodies are positioned or positioned so that between the two curved outer surfaces, a gap or at least one radiation absorbing low-absorbing area, a pinhole camera in almost any layer thickness can be imitated, which manages completely without mechanically moving parts. The restrictions on the ideal hole camera principle are low here. The low-absorbing radiation region may be filled with a suitable material which less absorbs the relevant radiation than the two bodies comprising the diaphragm, which material may be in the form of a separate insert or a coating applied to at least one of the outer surfaces , In the following, a gap is also to be understood as meaning a region which absorbs the radiation with little absorption and is filled with material. The description of the surface contour is based on a three-dimensional Cartesian coordinate system whose origin lies on the first curved outer surface without restriction of generality (cf. 2a ). The mode of operation of the diaphragm can be explained by considering a beam with a directional vector (1, y _s , z _s ), ie a beam which propagates in the direction of the positive optical axis x. For those ray bundles whose y-component vanishes and which can be described by a direction vector (1, 0, tan α) (cf. 2 B ), a straight line exists on the first curved outer surface, which runs parallel to the beam, if f (y) = tan α. If f (y) is a monotonically increasing or decreasing function, it is thus only possible to see through the resulting gap in a straight direction at one point. In other places, the radiation is absorbed more strongly.

ist.In a preferred embodiment of the invention, it is provided that the gap has a substantially constant gap width h (y) in a direction parallel to the optical axis x. The visible in the direction of the beam passage then has a size which is proportional to the expression

is.

If the gap width h (y) chosen so is that the said expression is constant, beams become more equal intensity mapped with the same imaging quality.

In a further preferred embodiment of the invention, it is provided that the surface contour of the first curved outer surface can be at least partially described by a function of the form z (x, y) = C x y x + n. C and n are constants. As a result, a particularly simple, linearly varying surface contour is specified, by which the hole camera principle can be ensured. The passage opening, which lets a beam pass through the directional vector (1, 0, tan α), moves in this arrangement for an increasing viewing angle α continuously from one side of the diaphragm to the opposite side.

Further it is preferred that the width of the gap is variable. hereby can the imaging properties of the iris to different situations, in particular to different intensities of the investigated radiation sources, be adjusted.

A particularly symmetrical arrangement is obtained when the two absorbent body cuboid are designed. In a linear varying and also symmetrical surface contour the gap appears at an angle of 45 ° when the depth b of the cuboid in the direction of the optical axis 2 / C.

There the aperture fulfills the ideal pinhole camera principle only for beam bundles whose directional vectors lie in the x-z plane is in a further embodiment of the Invention provided see that the two absorbent body to the optical axis x are rotatably arranged, so that the gap can be turned. Thus, you can several illustrations of an object are made which each containing a line for which ideal imaging properties exist.

When Building material for The panel is suitable for all materials that are able to effectively absorb the radiation emitted by the radiation source. In the case of X-ray or gamma rays are heavy metals with a high atomic number, for example, copper or tungsten. For neutron rays are against it Plastics with high hydrogen content, for example polyethylene, suitable.

Further advantageous embodiments of the invention will become apparent from the 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 imaging device with a diaphragm according to the invention;

2a an absorption element with drawn Cartesian coordinate system;

2 B a Cartesian coordinate system with a drawn direction vector in the xz plane;

3 an absorption element with marked beam paths;

4 an exploded view of a diaphragm according to the invention;

5a , b an aperture according to the invention from two viewing directions;

6 an aperture according to the invention with tilted gap;

7 an absorbent member from a variety of viewing angles;

8th an aperture according to the invention from a variety of viewing angles;

9 radiation passing through a slit for a plurality of viewing angles;

10 an aperture according to the invention in a shielding wall;

11 . 12 a first test arrangement;

13a , b, c, d test results with different diaphragm axis arrangements;

14 (schematically) a second test arrangement;

15 . 16 . 17 different views of the second test arrangement;

18a , b, c an illustration / reconstruction of the test body.

1 illustrates the hole camera principle on an imaging device 200 , From a radiation source 10 , for example, a test body, becomes high-energy radiation 12 , in particular X-ray or gamma radiation, emitted. The radiation 12 meets a panel 100 by which it is limited and along an optical axis x according to the Lochkameraprinzip on an imaging area 14 is directed. The picture area 14 is typically a projection surface on which an image of the test body 10 is produced. In the picture area 14 there is a receiving unit 16 which for the radiation 12 sensitive, in particular a detector or a camera.

The diaphragm according to the invention 100 comprises two absorption elements 18 . 26 , A first absorption element 18 is in 2a shown. It has a first curved outer surface 20 whose surface contour is in 2a not shown, to the orientation of their mathematical description. underlying Cartesian coordinate system. The position of the Cartesian coordinate system is chosen without restriction of generality such that its origin on the first curved outer surface 20 lies. The x-axis coincides with the optical axis. 2 B shows a Cartesian coordinate system with drawn direction vector, which lies in the xz plane. Radiation with such a direction vector whose y component disappears passes through the diaphragm according to the invention at a position at which f (y) = tan α.

3 shows the curved outer surface 20 of the absorption element 18 whose surface contour can be described by a function of the form z (x, y) = C x y x. The absorption element 18 is a cuboid, with respect to the coordinate system symmetrical body made of suitable absorbent material (width a, depth b). For hard radiation this is a heavy metal with the highest possible density, for example copper or tungsten. In 3 are ray paths 22a , b, which are parallel to the side edges 24a , b of the absorption element 18 run. The beam paths 22a , b correspond to direction vectors (1, 0, ± aC / 2). For every direction vector (1, 0, z) for which - aC / 2 <z <aC / 2, there is exactly one parallel edge on the curved outer surface 20 , For each direction vector with non-vanishing y component, the corresponding lines are on the outer surface 20 not linear.

4 shows an exploded view of the diaphragm according to the invention with the absorption elements 18 . 26 with complementary outer surfaces 20 . 28 , The absorption elements 18 . 26 are arranged so that between them a narrow gap with the gap width h is formed. The resulting aperture can be in a shield of shielding 30 to get integrated.

5a , b show the gap 32 between the absorption elements 18 and 26 for two viewing angles. Depending on the viewing direction is only at one point a view through the gap 32 in a straight line possible. In the respective direction thereby appears a parallelogram-shaped passage opening 34 , The splitting direction can optionally be horizontal ( 5 ) or vertical ( 6 ) be aligned. On the basis of a second image with such rotated aperture, distances to the object can be estimated on the basis of large-area contours and, if necessary, measured.

7 shows the absorption element 18 with curved outer surface 20 for a variety of viewing angles. The center of 7 corresponds to a directional vector (1, 0, 0) parallel to the optical axis. From this, the y-component of the directional vector of the viewing angle changes linearly in the horizontal direction, the z-component in the vertical direction.

8th shows for the same viewing angles as in 7 the absorption elements 18 . 20 , the gap between them 32 as well as the viewing angle dependent passage opening 34 , For viewing angles with a direction vector whose y component disappears, the trapezoidal passage opening shifts 34 laterally and while maintaining their shape and size (middle column, in 8th ). In the case of a non-vanishing y-component, that is to say in the case of a non-frontal view of the diaphragm, the passage opening decreases 34 , The ideal hole camera principle is thus for those points of the radiation source 10 fulfilled, which lie in the xz-plane.

9 shows a simulation of the through the aperture 10 absorbed radiation 12 and the resulting imaging point 36 passing through a point in the radiation source 10 in the picture area 14 is generated (same viewing angle as in 8th ). The shape of the picture points 36 are similar in the middle column of the 9 , while with increasing deviation from the ideal Lochkameraprinzip the imaging points 36 become blurred and weaker.

10 shows an aperture according to the invention 100 which is in a shielding wall 30 is integrated. A holder of the aperture 100 in the shielding wall 30 must not allow additional beam passage on the outsides of the two absorption elements 18 . 26 On the other hand, they must provide a firm hold in order to keep the gap width h set once constant.

11 shows an aperture according to the invention 100 which is in a tower of lead bricks 38 which is integrated by two lateral lead plates 40 is limited laterally. An x-ray flash tube 42 can on a tripod 44 be moved laterally at a fixed height ( 12 ). On the x-ray flash tube 42 opposite side of the panel 100 a sensitive selenium flat detector, not shown here, is arranged. Results of test series are in 13 reproduced, both with raised aperture 100 ( 13a and c, according to an orientation according to 6 ) as well as in a transverse orientation ( 13b , according to an orientation according to 5 ). In 13d all test results are superimposed in summary. The recordings in 13a and c were at different distances from the x-ray flash tube 42 (1.4 m and 0.9 m) made, the distortion angle through the curved gap 32 This shows a small difference. The picture of the point source 42 with horizontal aperture arrangement lie on a horizontal plane. In contrast to the other figures, the intensity of the laterally located points is relatively strong in comparison to the central point. In order to obtain an evaluable result, the number of emitted flashes would have to be increased many times over in the lateral recordings. This is at a vertical position ( 13a and c) not the case.

14 schematically shows a second test arrangement. A continuously radiating, powerful X-ray tube 46 generates radiation, which by an all-round shield, here a lead wall with window 48 , disappears. The through the window of the lead wall 48 passing radiation falls on an aluminum plate as scattering filter 50 , The actual test object 10 , here a lead brick with characteristic contours, is between the scatter filter 50 and the diaphragm of the invention 100 which are in a shielding wall 30 made of lead, arranged. As a detector 16 on the projection screen 14 serves a storage disk in a cassette.

15 . 16 and 17 show different views of the second test arrangement with and without stray filter 50 , The main axis of the aperture 100 is horizontal.

The illustration of the test object 10 on the storage disk 16 is in 18a played. The image is through the imaging mechanism with the help of the curved gap 32 distorted. The degree of distortion can be determined by means of straight-line structures. Absent such straightforward structures, it is about two shots, each with 90 ° rotated aperture 100 and a correlation of the respective figure. Such a correlation image is in 18b Darge presents. The closer the test object 10 at the aperture 100 is positioned, the stronger the distortion. An equalized picture is in 18 shown.

100

cover

200

imaging Facility

10

Radiation source / Test object

12

(High energy) Radiation / radiation field

14

Imaging area / projection

16

Receiver unit / detector / camera

18

(First) absorbent body / absorbent element

20

(first) curved outer surface

22a, b

Beam paths / radiation beam

24a, b

side edges

26

(Second) absorbent body / absorbent element

28

(second) curved outer surface

30

Shielding / shielding

32

gap

34

Through opening

36

imaging point

38

lead bricks

40

lead plates

42

X-ray flash tube / point source

44

tripod

46

X-ray tube

48

lead wall with window

50

Light diffuser / aluminum plate

Claims (12)

Cover ( 100 ), in particular for an imaging device ( 200 ), which is suitable from a radiation source ( 10 ) outgoing, in particular high-energy radiation ( 12 ) and along an optical axis x according to the Lochkameraprinzip to an imaging area ( 14 ), characterized in that the diaphragm ( 100 ) - a first the radiation ( 12 ) at least partially absorbing body ( 18 ), which has a first curved outer surface ( 20 ) whose surface contour can be described at least in part by a function of the form z (x, y) = f (y) x + n, and 12 ) at least partially absorbing body ( 26 ), which has a second curved outer surface ( 28 ) whose surface contour is at least partially complementary to the curved outer surface ( 20 ) of the first absorbent body ( 18 ), wherein the two absorbent bodies ( 18 . 26 ) are positioned or positionable such that between the two curved outer surfaces ( 20 . 28 ) A gap ( 32 ) or at least one radiation-absorbing area is present. Cover ( 100 ) according to claim 1, characterized in that the gap ( 32 ) or the radiation-absorbing area in a direction parallel to the optical axis has a substantially constant gap width h (y). Cover ( 100 ) according to claim 2, characterized in that the gap width h (y) is selected so that the expression

is constant at least in a partial area. Cover ( 100 ) according to claim 2, characterized in that the gap ( 32 ) or the radiation-absorbing area has a substantially constant gap width h. Cover ( 100 ) according to one of the preceding claims, characterized in that the upper surface contour of the first curved outer surface ( 20 ) can be described, at least in part, by a function of the form z (x, y) = C x y x + n. Cover ( 100 ) according to one of the preceding claims, characterized in that in the imaging area ( 14 ) one for the radiation ( 12 ) sensitive receiving unit ( 16 ), in particular a detector or a camera. Cover ( 100 ) according to one of the preceding claims, characterized in that the width of the gap ( 32 ) or of the radiation absorbing area low variable. Cover ( 100 ) according to one of the preceding claims, characterized in that the two the radiation ( 12 ) at least partially absorbing body ( 18 . 26 ) are configured cuboid. Cover ( 100 ) according to one of the preceding claims, characterized in that at least one of the two radiation ( 12 ) at least partially absorbing body ( 18 . 26 ) contains a heavy metal, in particular copper or tungsten. Cover ( 100 ) according to one of the preceding claims, characterized in that at least one of the two radiation ( 12 ) at least partially absorbing body ( 18 . 26 ) contains a plastic with a high hydrogen content, in particular polyethylene. Cover ( 100 ) according to one of the preceding claims, characterized in that the two the radiation ( 12 ) at least partially absorbing body ( 18 . 26 ) are arranged rotatable about the optical axis x, so that the gap ( 32 ) or the radiation absorbing area can be rotated. Cover ( 100 ) according to one of the preceding claims, characterized in that on at least one of the two the radiation ( 12 ) at least partially absorbing body ( 18 . 26 ) the radiation ( 12 ) at least partially absorbing shielding element ( 30 ) is attachable.