Patent GB-1090451-A (GB)
Title: Display apparatus for use with radiation detectors or the like
Inventor: SAUNDERS PATRICK WILLIAM
IPC: G01T1/29
Filed: 1964-03-13
Abstract: 1,090,451. Television; transistor amplitude discriminators; pulse circuits. E. K. COLE Ltd. March 8, 1965 [March 13, 1964], No. 10639/64. Headings H3P, H3T and H4F. [Also in Divisions G1 and G4] The invention relates to apparatus for producing a colour presentation of the distribution of scintillations radiated from a face of a crystal bombarded by penetrative radiation such as gamma rays. As shown a gamma camera 1, of the type described in U.S. Specification 3,011,057, which includes a plurality of phototubes viewing overlapping areas of the face of the crystal, is arranged to produce X and Y electrical signals proportional to the coordinates of the position of a scintillation and a Z electrical signal proportional to the energy level of the radiation causing the scintillation. These signals are fed to a storage device 3 via a pulse height analyser or gate 2 passing only Z signals within a given range of amplitude corresponding to the energy level of a particular desired radiation so that a " picture " of the scintillations from the desired radiation is built up in storage device 3 in the form of X and Y positional data for each such scintillation. Device 3 may comprise a magnetic store having analogue to digital converters in its input. To present a display whose colour rendering varies in dependence on the relative number of scintillations in different localities of the face of the crystal a scanning waveform generator 4 controls the deflection of the beam of a colour cathode ray tube 5 and the read out from storage device 3. The information from device 3 as to the number of scintillations stored is thus released in the correct time and positional sequence and fed to a decoder 8 whose output is fed as a luminance signal to the cathodes of tube 5 and also to a discriminator 9. Where the amplitude of the output of decoder 8 is proportional to the spot density, discriminator 9 is an amplitude discriminator and its output is passed to a colour difference amplifier 10 the output from which is applied as a chrominance signal to the Red, Blue or Green grid of the tube 5 so that different spot densities are represented in different colours. Where the output from decoder 8 represents a fine spot form of picture, each line scan consisting of a series of pulses the distribution of which is a function of spot density, discriminator 9 is arranged to discriminate between the intervals between successive pulses to give an output proportional to spot density. The output of the decoder may be taken over lead 11 to magnetic recording means. The discriminator circuit, Fig. 2 (not shown), comprises four Schmidt trigger circuits and has two output terminals (26) and (27), and is such that when the amplitude of the video signal is between 1 volt and 2À5 volts Schmidt trigger (14) (18) operates to provide a positive pulse at output terminal (26), Fig. 3(a) (not shown), between 2À5 and 3À5 volts Schmidt trigger (16), (20) also operates to provide positive pulses at both output terminals, and above 3À5 volts all four Schmidt trigger circuits operate but the outputs from trigger circuits (15), (19) and (17), (21) are phase inverted by transistors (24) and (25) and as the negative pulses so developed are arranged to have amplitudes in excess of the positive pulses developed by the first two trigger circuits, negative pulses are provided at both output terminals, Fig. 3(b) (not shown). The colour difference amplifier, Fig. 4 (not shown), is such that on a positive pulse being applied to terminal (26), a negative pulse is developed at the grid of valve (30) to provide a positive pulse at output terminal (34) which is used to turn on the red electron gun of the colour receiver. When positive pulses are applied to terminals (26) and (27), positive pulses are developed at terminals (34) and (35) to turn on the red and blue guns. When negative pulses are applied to terminals (26) and (27) the conduction of valves (30) and (32) and thus the voltage drop across resistor (36) is increased, reducing the current through triode (31) to provide a positive pulse at output terminal (37) to turn on the green electron gun. By a modification of the circuit arrangement and parameters the blue gun alone may be turned on instead of the red and blue guns.