GB1406685A - Sensing matrices for radioactivity-distribution detectors - Google Patents

Abstract

1406685 Radiation detectors BAIRDATOMIC Inc 13 Dec 1972 57614/72 Heading G1A [Also in Division H4] The distribution of radio-activity over an area is measured using a sensor comprising a two dimensional array of a certain number of scintillator elements coupled by light guides to a smaller number of photo-detectors in such a way that a scintillation in an element produces a signal from a unique combination of one or more of the detectors. As shown, Fig.1, the sensor comprises an array of scintillator elements arranged in alternately staggered rows making up a layer 28 light from which is conducted by light guides 30 having square ends transforming to cylindrical portions which terminate at individual detectors 14. The square ends of the light guides are larger than the scintillator elements and are positioned so that they cover the whole of one scintillator element and half of each of six surrounding elements. Each scintillator element is therefore coupled to a single one of the detectors or to a unique pair of the detectors. The outputs of the detectors are analysed to select pulses within a specific amplitude range or energy window and these pulses are passed by an address register 24 to a location in a memory 26 corresponding to the co-ordinates of the originating scintillator element. The outputs of the detectors are also applied to low level discriminators 18 connected to logic circuitry 20 which determines whether or not scintillations occurred in two or more elements simultaneously and produces a corresponding reject or accept signal which controls address register 24 so that false outputs due to simultaneous scintillations are not recorded, A suitable pattern for the arrangement of square scintillator elements and light guide ends is given, Fig. 4 (not shown) and this may be modified by making the ends of the light guides hexagonal, Fig. 6 (not shown). Either arrangement may utilize a plurality of first light guides, having pick-up ends as previously described, which are themselves coupled to further larger light guide ends which conduct the scintillations to the detectors, Figs. 5 and 7 (not shown). In this case each larger light guide covers half the area of four adjacent intermediate waveguides and is rectangular or trapezoidal in shape as appropriate. The scintillator elements may be of T1 activated Nal crystals or Cs crystals and the light guides may be of an acrylic resin such as methyl methacrylate, of clear epoxy resin, or of glass.