Apparatus for detecting the location of incident radiation

An apparatus for detecting a location of incident radiation, in which said apparatus has a plurality of sets of members where each set includes

• (a) a scintillation crystal;
• (b) a pair of photo-multiplier tubes having their photo-cathodes optically coupled to said scintillation crystal,
• (c) said scintillation crystal and said pair of photo-multiplier tubes forming a set;
• (d) a location detecting means coupled to said photo-multiplier tubes for specifying, from outputs of said photo-multiplier tubes, a location within said crystal at which a scintillation has taken place,
• (e) said scintillation crystal being comprised of at least three adjacent crystal segments arranged in a row in a first direction with two end segments being located at the respective ends of the row, each of said crystal segments being so coupled to each other to insure that a scintillation occurring in any one of the component crystal segments will cause said photo-multiplier tubes to deliver a substantially the same output irrespective of the location of occurrence of scintillation in said any one crystal segment and that scintillations occurring in the respective crystal segments will cause the photo-multiplier tubes to deliver outputs different in level with each other;
• and
• (f) in which the photo-cathodes of said pair of photomultiplier tubes face in a second direction transverse to said first direction, and where said sets form a ring, wherein those crystal segments in the respective scintillation crystals of the respective sets are arranged in parallel with each other.