Patent Number: 051446472
Section: claims

1. A radiation exposure field limiting apparatus for limiting an exposure field to be formed by radiations generated from a radiation generating equipment which includes a particle accelerator and a point radiation source, comprising a plurality of radiation shielding members in the form of plates for defining an exposure field of radiations, said radiation shielding members being mounted for individual movement relative to each other with respect to a plane of a center axis of radiations generated from said point radiation source to define an exposure field of radiations having an approximated profile to that of an object to be irradiated by such radiations, a face of each of said radiation shielding members at which the radiation shielding member contacts with an adjacent one of said radiation shielding members making part of a face of a circular cone having the apex at an imaginary radiation source which is imaginarily disposed at a point spaced by a significant distance from said point radiation source. 2. A radiation exposure field limiting apparatus as claimed in claim 1, wherein the imaginary radiation sources of said radiation shielding members are located at a common point on the center axis of radiations spaced from said point radiation source. 3. A radiation exposure field limiting apparatus as claimed in claim 1, wherein the imaginary radiation sources of said radiation shielding members are located at different points on the center axis of radiations spaced from said point radiation source. 4. A radiation exposure field limiting apparatus as claimed in claim 1, wherein the imaginary radiation sources of said radiation shielding members are located at a common point spaced from said point radiation source on an axis which passes said point radiation source and extends orthogonally to the center axis of radiations and also to the direction of movement of said radiation shielding members. 5. A radiation exposure field limiting apparatus as claimed in claim 1, wherein the imaginary radiation sources of said radiation shielding members are located at different points spaced from said radiation source on an axis which passes said radiation source and extends orthogonally to the center axis of radiations and also to the direction of movement of said radiation shielding members. 6. A radiation exposure field limiting apparatus as claimed in claim 1, wherein said radiation shielding members are disposed in a pair of opposing sets each including an odd plural number of such radiation shielding members, one of said radiation shielding members in each set which is located at the center of said radiation shielding members of the set and defines a portion of an exposure field of radiations which intersects the center axis of radiations having a pair of faces at which the one radiation shielding member contacts with adjacent ones of said radiation shielding members of the set and which make part of flat planes which extend in parallel to the center axis of radiations while each of the other radiation shielding members of the set has a pair of faces which make part of a face of a circular cone having the apex at said imaginary radiation source of the radiation shielding member. 7. A radiation exposure field limiting apparatus as claimed in claim 6, wherein also each of an adjacent pair or pairs of the other radiation shielding members in each set on the opposite sides of the center radiation shielding member has a pair of faces which make part of flat planes which extend in parallel to the center axis of radiations.