Patent Number: 047456310
Section: description

As may be seen in the drawing FIGURE, a source 1 of x-rays generates x-rays which through a collimating slit 2 defines a coarse fan beam 4 of x-rays. The slit is formed in a plane of x-ray absorbant material 3 and placed for directing the fan beam 4 onto a flying spot generator 5. The flying spot generator 5 consists of an even number of helical shaped x-ray windows 6' and 6", for example, which have been provided in a cylindrical shell 5. The cylindrical shell 5 is of x-ray opaque material, such as lead. A practical device, however, could be formed of three concentric cylindrical shells in which an inner core is a shell of aluminum or other low x-ray absorbing material, an intermediate shell is of lead with the lead completely machined away in the requisite helical pattern, and an outer shell or cover of thin, low x-ray absorbing stainless steel. This arrangement could be approximately 12 inches long and 4 inches in diameter, and supported in a manner to permit rotation around its length. Such rotation may be at 3600 rpm with the support being by way of splitrace roller bearings along its length. The split helical pattern permits transmission of x-rays. The number of x-ray windows 6' and 6" need to be of an even number, such as the two illustrated in the drawing FIGURE. The windows are slits of a helical shape on opposite sides of the cylindrical shell, and the flying spot 10 appears when the two helixes 6' and 6" intersect in the field of an incident x-ray beam. Upon rotation of the shell the flying spot 10 transmitted through the flying spot generator 5 moves in a linear directon 13 from one end of the flying spot generator to the opposite end. Because of this movement of the flying spot, a single detector 7 is provided to detect an object 8 moving along a conveyor belt 9. The conveyor belt movement is in the direction 11, for example. The detector 7 could be a single wire, long, high pressure gas counter tube. Such an arrangement might be filled with xenon and operated in a current measuring mode with a gas gain of the order of 10.sup.2 to 10.sup.4. The detector 7 could also be a photomultiplier with a long scintillator. In this arrangement, an object 8 passing on the belt 9 would move through the moving flying spot which would pass back and forth over the object. The rotation of the shell or flying spot generator 5 generates the linear motion of the x-ray flying spot which passes along the detector 7. Image formation is retrieved from the detector by electronically sampling the detector signal and correlating the time of sampling with the angular position of the rotating shell. In a practical arrangement of the present invention, the helical windows 6' and 6" in the flying spot generator 5 are x-ray windows passing x-radiation. However, modifications to use gamma ray radiation, or other radiation, are also suitable. While a single arrangement of the present invention has been illustrated and described, the present invention includes all variations and features which may be evident from the claims.