Patent Number: 042008034
Section: description

In the basic example of a multiple collimator shown in FIGS. 1 to 3 spherical cavities are provided in two of the three bores passing through the shield plate 1, into each of which a portion of the collimator tube 4 is so engaged that a ball joint is formed in each case, and the collimator tubes 4 are accordingly arranged to swivel about the respective ball joints. In order to provide a swiveling range of a width sufficient for the various examinations of objects containing a radioactive source, the remaining portion 5 of the bores here under discussion are extended in conical shape for a part of their axial length. As is particularly clear from FIG. 3, as a result of this configuration it is made possible to set the position of the detectors 6 that are inserted in the collimator tubes 4 suitably to the desired requirements. The bores 7 defining the inside of the collimator tubes 4 are shaped conically for better focusing. It is of course possible also to make the bores through the collimator tubes 4 cylindrical. By the provision of the widened spherically shaped portion 3 of the collimator tube 4, in combination with the remaining portion of the shield plate 1, a sufficient shielding against the penetration of disturbing rays into the measuring detectors 6 mounted on the collimator tubes 4 is provided. In the first embodiment of a multiple collimator apparatus of the present invention illustrated in FIGS. 4 and 5, just as in the one shown in FIGS. 1 to 3, there are provided one fixed and two movable measuring detectors. The shield body 1 is again of more or less frustoconical form and in it, in addition to the fixed collimator bore 22 there are two conical bores for seating the adjustable collimators. On each of the conical bores there is mounted in a ball bearing 8 a body 9 that has a prismatic cavity 23 in which the stem portion of rectangular cross section of an adjustable collimator 4a is mounted so that it can pivot on pivot studs 10 journalled in the body 9, only one of these studs 10 being shown, diagrammatically, in FIG. 5. The rotational position of the body 9 can be read off at the index mark 12 from the circularly arranged scale 11. The adjustment of the collimators can be read on an arc-shaped scale 13 at the index mark 14 carried on the collimator. By actuating a push-knob 15 that, when pushed in, presses down a clamping spring (not shown) at the side wall of the body 9, the latter is set free to revolve on the bearing 8 so that its position can easily be set. Release of pressure on the knob 15 causes the unshown spring to hold the body 9 in the set position. For swinging the movable collimator about its horizontal pivot axis, the knob 16 is pressed in, pulling off a clamping spring (not shown) from the inner surface of the cone, allowing the collimator body 4a to pivot. Release of the protruding button 16 causes a spring to hold the collimator body 4a in position. By inserting of small chocks such as the chock 17 shown in FIG. 5 the gaps in the shielding body can be practically prevented from reducing appreciably the extent of shielding of the collimators from any direction. In the form of construction illustrated in FIGS. 6 and 7, just as in the form shown in FIGS. 4 and 5, in each of two generally conical bores there are provided frustoconical bodies 9 that are mounted in ball bearings 8 for rotation about their respective axes of symmetry. These axes could be slightly off the vertical as shown in FIG. 5, but FIG. 7 shows that the frustoconical body 1 can be arranged to provide for a vertical axis for the body 9 revolving in a conical bore in the body 1. It is held against rotation in its bearings by a spring stud, not shown, that can be taken out of engagement by pressure on the button 15 so that the body 9 can revolve. The angle of rotation can be read off at the index marker 12 on the scale 11 marked on the circular rim of the top of the body 9. As can be seen from FIG. 7, an eccentric conical bore is provided in the body 9, in which a collimator tube body 4b is held rotatably by means of the ball bearings 18. The collimator tube body 4b has an eccentrically located collimator bore in the top of which a detector is located at 6. When the body 4b is rotated in its ball bearing 18 so that the axis of the collimator bore coincides with the axis of rotation of the body 9, in the particular position illustrated in FIG. 7, it is then vertical and this position can be indicated on the rim scale of the collimator body 4b as the zero position, as shown in FIG. 6 opposite the scale index marker 20 engraved in the body 9. By revolving the collimator body 4b about its axis 4c, the axis 4d of the collimator bore increases its inclination to the axis 9a of the conical body 9 from zero in the position shown in solid lines in FIG. 7 to a maximum reached by a rotation of 180.degree. into the position shown in dotted lines in FIG. 7. The inclination of the axis 4d of the collimator bore to the axis 4c in the illustrated case, which is also the inclination of the axis 4c to the axis 9a, is 15.degree.. The scale 19 is so subdivided that each scale division marks an amount of rotation that corresponds to an inclination increase of 3.degree.. The collimator body 4b is also provided with a stopping or holding device (not shown) that can be disengaged by pressing on a button 16. The form of multiple collimator apparatus shown in FIGS. 6 and 7 lends itself to aiming each collimator unit at a particular point P in an object plane by reference to polar coordinates, in which case the scale 19 can adjust the length of the radius from a point of origin and the scale 11 an angle defining the radius vector. The adjustment of the collimator to aim it at a point P is carried out, for example, by turning the collimator body 4b by rotation to the right up to scale division 4, which swings the collimator off the vertical by 4.times.3.degree.=12.degree.. As shown in FIG. 6, this brings the aiming point of the collimator from the center of the diagram through an arc shown by a dotted line to a point Q on the circle 25 which has a desired radius. The rotation movement is indicated by the arrow 26. Then body 9 is rotated to index the second scale division and the effect on the aiming point of the collimator is indicated by the arrow 27. This brings the collimator to the point P. Thus the pair of scale coordinates 4, 2 used in this case uniquely defines the point P and the collimator can be reset to that point after having been moved in the meanwhile to some other position. The particular advantage of the form of construction shown in FIGS. 6 and 7 for a multiple collimator according to the invention is that the shielding of the detectors has no weak spots formed by cavities or gaps and indeed has no asymmetry, while the reading off of polar coordinates is unusually convenient. Although the invention has been described with reference to particular illustrative examples, it will be recognized that modifications and variations are possible within the inventive concept. Thus, for example, collimator bodies swiveling about a defined axis like the collimator bodies 4b of FIG. 4 could be journaled directly in the shield body 1 as in FIG. 1 (i.e. forming a roller joint instead of a ball joint) rather than in rotary intermediate bodies 9 as in FIG. 4. This would restrict adjustability, but it might be usefil where the collimators are designed to be all aimed at a selectable point on the fixed axis of a fixed collimator, in which case the swivel collimators would swing about horizontal axes perpendicular to the axis of the fixed collimator.