Patent GB-1497284-A (GB)
Title: Detector for locating particles
IPC: G01T1/18
Filed: 1974-12-19
Abstract: 1497284 Radiation detectors COMMISSARIAT A L'ENERGIE ATOMIQUE 19 Dec 1974 [21 Dec 1975] 54934/74 Heading G1A [Also in Division H1] A detector for locating particle radiations comprises a sealed chamber filled with a fluid and containing a first electrode constituted by at least one conductive wire and a second electrode constituted by at least one conductive plate, so disposed that the plane angle subtended by the or each plate at any point on the wire in a plane perpendicular to the wire varies with the distance of the point along the wire. The cylindrical outer electrode of a proportional ionization tube Fig. 2a for detecting charged or neutral particles, x-rays or γ-rays, comprises a pair of half-cathodes 14, 16 insulated from each other and of complementary shapes such that an ionization event occurring near a point on an anode wire 12 gives rise to complementary charge pulses in the leads 18, 20 Fig. 2b whose difference, expressed as a fraction of their sum, is a function of the position of the point along the anode wire 12. The cathode, when developed, may take the form of a pair of interengaged arrays of isosceles triangles Fig. 3 (not shown) having their axes of symmetry parallel to the cylindrical axis. In a second embodiment Fig. 9 a planar array of parallel wire anodes 54 has on one side a planar cathode 70 comprising interengaged isosceles triangles 74, 76 with their axes of symmetry parallel to the anodes 54. A second cathode 72 on the other side shaped similarly to the first, is disposed with the axes of symmetry of the triangles 74', 76 transverse to the anodes 54. The cathodes 70, 72 locate an ionization event in the X and Y directions respectively. Alternatively Fig. 5 (not shown), the anode array (54) is arranged between two cathodes (42, 44) each having its triangular elements directed parallel to the anodes (54) for locating an event in one direction only. In a third embodiment, Fig. 7, the half-cathodes comprise interengaged teeth 82a-h separately insulated, those with left-facing bases being connected along a resistance chain R 1 -R 3 , those with right-facing bases being connected along a resistance chain R' 1 -R' 3 . The signals at terminals B, E, B', E of the two resistance chains are combined in various combinations of addition, subtraction and division to obtain co-ordinates of an event within the electrode area.  In a fourth embodiment, Fig. 8, complementary half-cathodes are constituted by rows of triangular elements joined base-to-base and apex-to-apex alternately 110a, 110b (similarly 110c, 110d), an array of wire anodes being arranged transversely to the axes of symmetry of the triangles. Measurement of the difference between half-cathode pulses indicates precisely the location of an event in relation to an indeterminate one of the triangular elements, the element being identified by determining which anode receives the greatest share of the pulse. Other embodiments Figs. 4, 6 (not shown) include tubes wherein part of the cathode is discontinuous, a window permeable to x-rays being provided near the discontinuity. The fluid filling the sealed chamber may be a gas; or, for locating high-energy γ-rays, liquid xenon may be used.