Patent Number: 063242591
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the form of a basic diagram, FIG. 1 shows a plan view of an inventive scattered-ray grid 1. The grid 1 is composed of a silicon carrier 2 and of a number of rows 3 of pin-shaped absorption elements 4 made of lead, which are introduced in holes that are etched into the carrier 2. Only a few of the absorption elements 4 are specifically shown; it will be understood that each row 3 is composed of a number of such elements. The etching process ensues by means of an etching mask, which can be produced by means of a photo technique with which the configuration of the row arrangement can be fixed in a simple way. The scattered-ray grid 1 can be divided into a number of grid sectors, such as six individual grid sectors I-VI, the configuration of the rows 3 being the same in all six grid sectors. For clarity, the row arrangement is only indicated in sector I. Apart from the rows 3a that respectively extend through the center Z and that border the sectors, the rows 3 start at respectively different radii and are directed toward the center Z, as can be seen from FIG. 1. FIG. 2 shows a portion of FIG. 1. The determination of the position of the origin of every row is shown in FIG. 2. Every row radially proceeds to the periphery of the carrier 2 and has its origin in the space r.sub.0 +n.DELTA.r from the center Z. Therefore, .DELTA.r, as a radial increment, determines the density of the rows; the start radius r.sub.0 optimizes the density of the rows in the center. n is an integer. A relevant space r.sub.0 +n.DELTA.r is shown in FIG. 2 as an example. A location is now to be selected within this space, at which the origin of the (next) row 3.sub.n is to be placed. The largest angular spacing between all existing adjacent rows, which intersect the circle or arc of circle with the origin radius, namely the space r.sub.0 +n.DELTA.r, is searched for this purpose. In the example, the two rows 3b are spaced from one another around the largest angle a. This angular spacing now determines the angle section, which is to be divided in a predefined ratio p:q, so that the exact position of the origin u of the new row 3.sub.n between the two rows 3b results therefrom. p and q can be rational numbers or irrational numbers. The best distribution results for p.noteq.q. In the described way, the position of each new row is determined in iterative fashion by taking the two rows 3a that start (originate) in the grid center as a basis. The described iteration condition generates an extremely homogenous radial row pattern, but it can nevertheless exhibit spiral-shaped density variations although they are almost negligible. In order to substantially avoid such density variations, a different version of the iterative method is provided, which is explained in detail in FIG. 3. In this version, for determining the position of the new row 3n, the angular spacing is also determined for each row pair that intersects the circle or arc of circle with the origin radius r.sub.0 +n.DELTA.r, as described with respect to FIG. 2. Subsequently, the angular spacings to the two rows respectively on opposite sides of the adjacent rows are determined. In the shown example, these are the angle spaces b and c respectively between the two pairs of rows 3b and 3c. The sum S=a+F (b+c) is formed on the basis of the angle spacings a, b, c, with the sum of the two angle spacings b and c being weighted with a predefined factor F, which is &lt;1, within the sum S. The largest sum S is now selected from the cumulative values determined for each row pair at the relevant radius, and the angle section associated with this largest sub S is divided in the given ratio p:q. The width of a row is dependent on the diameter of the pin-shaped absorption elements 4 and is in the range of a few .mu.m; the start radius r.sub.0 is 30 .mu.m, for example; the individual radius step or increment .DELTA.r is 100 .mu.m, for example. In addition n is element of the natural numbers including zero. The described iterative algorithms make it possible to determine the position of the rows in a simple way, so that highly homogenous scattered-ray grids can be generated. Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art.