Patent GB-990192-A (GB)
Title: Improvements in or relating to dosimeters
Inventor: COOKE-YARBOROUGH EDMUND HARRY
IPC: G01T1/15
Filed: 1962-05-21
Abstract: 990, 192. Nuclear radiation dosimeter. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. May 13, 1963 [May 21, 1962], No. 19448/62. Heading G1A. In a total radiation dosimeter for nuclear radiations, comprising an ionization chamber having inner and outer electrodes, the chamber is initially charged and the outer electrode is raised progressively in potential until the inner electrode is pulled in potential up to a threshold value, whereupon, the potential of the outer electrode falls rapidly to its initial level, and the cycle is repeated, a momentary warning being given each time the threshold level is reached and the arrangement being such that, in the presence of ionizing nuclear radiation, the time intervals between successive warnings decreases progressively as the potential difference between the electrodes slowly falls owing to the increasing ionization current flowing in the chamber. In the arrangement of Fig.2,capacitor C charges up to potential V2, causing the chamber to charge up to the same potential owing to the flow of grid current in valve E, and then causing relay 6 to close the contact short-circuiting the capacitor, bringing the potential of the outer chamber electrode down to V1 and the potential of the grid of valve E down to -(V2-V1). During operation the capacitor C charges through resistor R, so that the outer electrode potential rises towards V2. The potential of the valve grid therefore rises, causing a corresponding increase in the input to trigger circuit 3. Since the potential of the inner electrode and the valve grid is below that of the outer electrode by an amount depending on the amount of ionization of the gas within the ionization chamber, which is turn depends on the total amount of ionizing radiation absorbed by the gas, the time which elapses before the triggering level of circuit 3 is reached depends on the said amount of radiation. When the trigger circuit 3 is operated oscillator 4 is energized to give an audible warning, and relay 6 is also operated such that the capacitor is short circuited and the potential of the outer electrode falls to V1. The relay is now de-energized opening its contact and the capacitor recharges, repeating the cycle. As the amount of ionization in the chamber 1 increases the time between successive audible warning will become less, until a continuous tone indicates that a dangerous dosage has been received. When the circuit of Fig. 3 is first switched on capacitor C3 charges up through resistor R3 and the emitter/base junction of transistor J1, whereby transistor J2 is turned on via broken down Zener diode Z2, which in turn turns on oscillator 4. The output of the oscillator is amplified and rectified in 7 and the resulting D.C. current is fed, via the emitter/base junction of transistor J1 and diode D2 to charge up capacitors C1 and C2. This continues until the potential across the capacitors and Zener diode Z1, reaches V2,when the Zener diode breaks down and the output of the rectifier 7 is shunted thereby. The positive sides of capaci- C1 and C2 is approximately of the potential V1 of battery B1, whilst the potential of the negative sides is -(V2-V1). Switch S is now moved up, discharging capacitor C2 (capacitor C1 remaining charged due to diode D1) such that the negative sides of the capacitors are pulled up to a potential of V1 and the positive side of capacitor C1 and the outer electrode of the ionization chamber 1 is thus raised to a potential of (V1 and the positive side of capacitor C1 and the outer electrode of ionization chamber 1 is thus raised to a potential of (V1 + V2). Screen grid current starts to flow through valve E, until the chamber is charged to the potential (V1 + V2), i.e. the screen grid is at zero potential. Switch S is now returned to its lower position such that the negative side of capacitor C2 is again charged to a voltage of -V2 with respect to its positive side, thus lowering the potential of the outer chamber electrode to V1 and control grid of valve E to -V2. Since capacitor C2 is no longer being charged it commences to discharge through resistor R1 and diode D3, thus causing the potential of the positive side of capacitor C1 and the outer chamber electrode to rise. The potential drop across the ionization chamber will depend on the degree of ionization therein, such that the screen grid of the valve will reach the threshold or turnings on potential quicker if a large amount of ionization is present. When the valve E starts to conduct, transistor J1 is turned on which in turn turns on transistor J2 and the oscillator 4, to give a warning audio signal. The output of oscillation 4 is also rectified and fed to recharge the capacitors such that the cycle is repeated. A visual instead of an audio may be given