Patent GB-963580-A (GB)
Title: Improvements relating to radio-activity contamination monitors
Inventor: BROWN JAMES ROBERT
IPC: G01T7/12
Filed: 1959-10-06
Abstract: 963,580. Radio-activity measurements. ELECTRIC & MUSICAL INDUSTRIES Ltd. Sept. 28, 1960 [Oct. 6, 1959], No. 33756/59. Heading G1A. [Also in Division H3] A radio-activity monitor comprises a detector producing signals of amplitude dependent on the masses of incident particles and means for separating these signals to obtain separate indications of the densities of radiation of the different particles. The detector or probe 1, Fig. 1, is formed of a dual phosphor scintillation counter from the photomultiplier of which are produced signals on receipt by the rear phosphor layer of #-particles and larger signals in response to o-particles impinging on the front zinc sulphide layer. These signals are supplied to two identical trigger circuits 3 and 4 via an input circuit 2 in which the signals to the trigger circuit 4 are so attenuated that it does not respond to the probe output corresponding to a #- particle. Hence on receipt of an alpha-particle both trigger circuits respond, whereas a #-particle occasions the operation of only trigger circuit 3. The outputs from these trigger circuits are supplied to a switch unit which connects with an anticoincidence circuit 6, a ratemeter circuit 7, a tone circuit 8, a loudspeaker 10, a meter 9, and a mechanical register 11. The arrangement provides, according to switch position, either indication of the incidence of alpha -particles by the mechanical register (position a) or of alpha-particles (position b) or #- particles (position c) or both (position d) by the meter 9, and for each an audible indication from the loudspeaker by sounds distinctive to each particle type. Each trigger circuit Fig. 3 (not shown) comprises a monostable circuit which serves as a pulse shaper, the output pulses being supplied via the switch unit to the anticoincidence circuit. This comprises two emitter followers T6 and T7, Fig. 4, with respective input leads A and B, whose outputs are applied to the base and emitter respectively of a further transistor T8 so that the circuit produces a pulse output to the ratemeter circuit only when only one of the input leads A or B is pulsed. For monitoring alpha- and #-particles, trigger circuit 3 is connected to A. For alpha-particles only, trigger circuit 4 is connected to B (in each case the "spare" input lead being earthed via the switching unit) whilst for monitoring only #-particles both trigger circuits are connected. In the ratemeter circuit there are two emitter followers in series which supply an output E, Fig. 6, to the tone circuit and another to three diode pump circuits in parallel which supply current via an output G to the meter 9, Fig. 1. The time constants of the diode pump circuits differ so that their relative contributions to the meter current varies with counting rate so as to give an approximately logarithmic relation between the meter indication and counting rate. The tone circuit comprises an oscillator T10, Fig. 5, whose signals may be gated to the loudspeaker which is connected to an output lead J. In response to a pulse corresponding to an alpha-particle arriving at an input D a monostable circuit formed of transistors T13 and T14 is switched to its unstable state during which the oscillatory signal is fed to the output J via a further transistor T11, so that each alpha-particle occasions a "squeak" from the loudspeaker. Pulses corresponding to #- particles are supplied to a transistor T12 so as to cause a click " from the loudspeaker to identify them. A further output is taken from this circuit at H in the form of a pulse from the monostable circuit to the mechanical register so that this may count the incidence of alpha-particles for low incidence rates.