Patent Number: 055043445
Section: description

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now more specifically to the drawings, FIGS. 1 and 2 are intended to schematically represent a typical radiation source containment vessel or container 10 and a closure or sealing unit 12 for an access opening or port 14 within the container 10. As will be recognized, the closure, particularly in the larger more bulky assemblies, must be readily assembled to, and removed from, the container 10 by remote and/or robotic means without binding or jamming. This, particularly when considering what might be substantial expansion and contraction of the two components 10 and 12, necessitates what, with regard to radiation flow, comprises a substantial gap between the peripheral walls of the container and closure. The radiation shield 16 of the invention reduces radiation streaming from the generated isotropic radiation flux of a source within the container 10 to a degree substantially beyond what has heretofore been achieved by conventional shield member interface configurations. The radiation shield 16 of the invention restricts, and in fact prevents laterally dispersed or angled photon flow from the radiation source outwardly through the gap, and limits the flow to only those photons which are collimated. This is achieved by providing each of the surfaces defined by the peripheral wall of the port 14 and the peripheral wall of the closure 12 with a series of alternating ridges 18 and grooves or valleys 20 uniformly configured for a complementary and mating engagement of the port wall surface with the closure wall surface. As suggested in the drawings, the respective heights and depths of the ridges and valleys are such as to provide for a substantial interdigitation or mating interlock whereby no unimpeded lateral, i.e., non-collimated photon, flow within the formed gap is possible, notwithstanding substantial gap tolerances and variations thereof due to expansion and contraction as required by the nature of the components. The relationship between the interdigitated surfaces will be readily apparent from the enlarged cross-sectional details of the principal trigonal interface of FIGS. 7 and 8 and the alternate configurations of FIGS. 9, 10 and 11 which respectively illustrate a rectangular interface, a circular interface and a parabolic interface. As previously indicated, FIG. 5 schematically illustrates the unimpeded photon flow between opposed planar surfaces of a conventional shield interface. In contrast, the schematic illustration of the radiation shield 16 of the invention, as illustrated in FIG. 7, clearly demonstrates the effectiveness of the shield wherein photons other than those few specifically collimated relative to the ridges 18 and valleys 20, will encounter immediately adjacent ridges for collision with and absorption by the material, e.g., steel, of the ridges and valleys at the point of engagement therewith before reaching the target point. Due to minimal reflection of photons, e.g., an albedo in the order of 1%, and continued collision and absorption, the streaming of photons outwardly of the source container will be substantially eliminated. With continued reference to the schematic illustration of FIG. 7, it will be appreciated that the greater the length of the radiation shield in the direction from a radiation source in the container to ambient, the greater the likelihood of collision with and thus absorption of photons within the ridges with corresponding reduction of streaming by any photons other than those exactly collimated or paralleling the interdigitated ridges and valleys. Referring again to the exemplary embodiment of FIG. 2 with respect to a containing vessel 10, it will be recognized that the parallel ridges and valleys of the radiation shield 16, extending parallel to the direction of movement of the closure 12 relative to the containing vessel 10, allow for a smooth unimpeded engagement of the closure and subsequent removal of the closure. As desired, appropriate locating means, stops or the like can be provided to define or limit inward travel of the closure within the containing vessel. For example, a prior art stepped shield, as in FIG. 3, can be used in conjunction with the radiation shield of the invention both to provide a locating means and to even further enhance the efficiency of the shielding effect. In such a combination of shield configurations, as suggested in FIG. 13, it will be appreciated that the ridge and valley shield of the invention will be defined between all opposed parallel faces of the container and closure surfaces. Referring to FIG. 12, the triagonal interface therein has been illustrated with ridge and valley angles of 90 degrees. This particular geometry results in a situation where the gap between the shield surfaces is only 70.7% of the "tolerance" distance between shield sections. This means that the tolerance difference between sections can be 41.4% greater than the gap set. This is an important advantage as one wants to reduce the gap as much as possible to restrict the radiation streaming, while at the same time increase the tolerance distance as much as possible to accommodate changes such as the thermal expansion of the components, and also to compensate for manufacturing intolerances. If the 90 degree angle is increased or decreased, this particular advantage will decline until the gap is equal to the tolerance distance. From the foregoing, it will be recognized that a significant advance has been made with regard to radiation shielding within necessarily occurring joinder gaps. The enhanced photon absorption effectiveness, and thus anti-streaming characteristic, is achieved without interference with the ability of the components to be assembled and disassembled in the conventional manner, such normally being effected remotely in a secured environment, possibly by robotic means which necessitates a degree of tolerance between the components sufficient to avoid jamming or misalignment. The shield of the invention effectively eliminates radiation streaming other than that which is collimated or travelling strictly in a linear direction along the interdigitated ridges and valleys. When optionally combined with a stepped shield interface, as suggested in FIG. 13, the minuscule streaming of remaining collimated photon flow can itself be further reduced, if not in fact practically eliminated. The foregoing described embodiments of the ridge and valley shield are illustrative of the invention. As other embodiments incorporating the inventive features may occur to those skilled in the art, the disclosed embodiments are not to be considered as a limitation on the scope of the invention.