GB781875A - Improvements in and relating to amplifying systems - Google Patents

Abstract

781,875. Measurement of radio-active radiation. INDUSTRIAL MACHINERY CO., Ltd. July 21, 1955 [April 21, 1954], No. 11488/54. Class 40 (3). Apparatus for measuring a first parameter of radio-active radiation comprises a radiation detector feeding an amplifier which produces an output voltage in accordance with said parameter and a further output voltage which is a function of a second parameter of the radiation and of the detector sensitivity and the amplifier gain, and means for using the further output for controlling the amplifier gain and/or the detector sensitivity. In the embodiments the first parameter is the number of pulses exceeding a predetermined amplitude and the second is the average amplitude of output pulses from the amplifier. In the Fig. 3 embodiment the detector (not shown) comprises a scintillator, a photo-multiplier responsive to the scintillations and a conventional preamplifier to output pulses from which are fed via delay line DL and amplifier V2 to amplifier V3A, V3B. The gain of the latter is controllable by varying the control grid voltage and hence the impedance of pentode V4 which is a cathode load common to the valves. The amplifier output is transformer coupled to the input of voltage amplifier V5, V6, V7, provided with negative feedback via the common cathode resistor R5 of valve V5 and the cathode follower V7. Output pulses from the latter are fed to the valve V8 which is cathode coupled to V9. A pulse exceeding an amplitude determined by the negative voltage tapping on potentiometer R10, R11, R12 produces a pulse at the cathodes of amplitude proportional to the amount by which it exceeds the predetermined amplitude, and a pulse in the opposite sense at the anode of V9 of fixed amplitude. The pulses are applied through diode pump circuits V11, V12 respectively to capacitor C2 the voltage across which is therefore a function of the average pulse amplitude. The voltage is fed to buffer and amplifier stage V13 comprising a pair of cathode coupled triodes. A fraction of the output voltage derived from potentiometer R15, R16 is applied to control the impedance of V4 and hence the amplifier gain. The charge passed to capacitor C2 is made independent of the voltage across it by feeding the diode pumps with voltages tapped off the load of cathode follower V15. The constant amplitude pulses from V9, after amplification in double triode cathode follower stage V16 are fed, e.g. to a ratemeter. In an alternative embodiment the second voltage is applied to the screen grid of a valve operating as a conventional R.F. E.H.T. generator supplying H.T. to the photomultiplier to control its sensitivity. A circuit for this purpose is shown in Fig. 1. V31 and V32 function as V8, V9 in the above-described circuit to charge capacitor C33 via diode pumps V33, V34 and a Miller integrator which includes pentode V35 and cathode follower V36A. V36B, V37 function to adjust the cathode voltage of V35 in accordance with the value of the unstabilized H.T. so that the generator valve heaters may be fed from an unstabilized supply, while diodes V38A, V38B set lower and upper limits to this voltage. The voltage across C33 is fed to the generator, while the constant amplitude pulses from V32 are amplified in V39 and counted. Reference has been directed by the Comptroller to Specification 732,353.