Patent GB-997328-A (GB)
Title: Improvements in or relating to methods of and apparatus for detecting the direction of incidence of a radioactive emission
IPC: G01T1/29
Filed: 1963-08-07
Abstract: 997,328. Detecting radio-active radiation. ATOMIC ENERGY OF CANADA Ltd. Aug. 7, 1963 [May 23, 1963], No. 31226/63. Heading H4D. A method of detecting the incident direction of radio-active radiation from a source 4, Fig. 1, comprises dividing the radio-active radiation incident at the point of measurement into two zones by a plane of division 3, detecting the radiation count in each zone and deriving a signal from the ratio of the two counts having a sign dependent on which zone has the higher count, and rotating said plane of division until the signal reduces to zero thereby indicating that the plane is aligned with the direction of the source. In Fig. 1, 1 and la indicate a pair of radiation counting tubes connected to respective switches 2 and 2a, and separated by a radiation absorbing shield 3. The outputs of the switches are connected across a centre zero meter 8. The switches comprise a two transistor bi-stable circuit, Fig. 3 (not shown) such that when a pulse is fed by one switch and passed therethrough to the meter, the other switch is automatically turned off. The meter circuit comprises capacitive averaging means variable for a fast or a slow counting rate, such that the meter reads the difference between the average radiation counts detected by the counting tubes, which difference becomes zero to give a centre scale indication when the radiation counts are equal, with the shield 3 aligned with the direction of the source. The meter can be arranged such that the position of the meter will in general point to a side of the centre scale indicative of the side of the shield receiving the larger radiation such as to point to the source of radiation. Counting tubes 11 and 1a<SP>1</SP> may be added in series with the counting tubes 1 and 1a respectively, either as shown or along a line perpendicular to the plane of shield 3. Where a slower counting rate is required a different set of counting tubes may be used. The embodiment described is such that its resistivity is maximum when the plane of the shield 3 and the source 4 are aligned (see Fig. 6, not shown). In another embodiment, Fig. 7 (not shown), a source of radiation may be placed just in front of the shield 3, with additional shielding means behind it, and the counting tubes may detect radiation from the source as reflected by a distant object. The counting tubes and shield constitute a probe which may be separate from or combined with the switches, and the meter 8 may likewise be separate from or combined with the switches. Transistors used in the embodiment may be replaced by valves. The instrument may be calibrated by placing a source on the axis of symmetry and either rotating the shield about an axis, or by moving the counting tubes relative to the radiation source on reflector. The apparatus may comprise automatic gain control circuits to compensate for variations in the strength of the source. Applications of the instrument may be, locating contamination around reactors or places where radio-active sources are used, locating " hot spots " on areas of fall-out in military application, locating lodes of radio-active ones, locating malignancies in patients by use of a radioactive tracer, locating transducer cells in patients carrying a small amount of gamma radio-isotope, and, using the embodiment of Fig. 7, the location of pipes in walls and seams in mines.