Patent GB-421341-A (GB)
Title: Improvements in or relating to apparatus for detecting, counting or otherwise measuring corpuscular radiations
IPC: H01J47/08
Filed: 1933-06-21
Abstract: 421,341. Detecting and estimating radiation. WILLIAMS, C. E. WYNN-, Bron Haul, Church Walks, Llandudno, Carnarvonshire, and CAMBRIDGE INSTRUMENT CO., Ltd., Chesterton Road, Cambridge. June 21, 1933, No. 17637. [Class 97 (iii)] [See also Groups XXXVI and XL] Relates to apparatus for detecting or counting corpuscular radiations, e.g. alpha particles, beta-particles, moving electrons, cathode rays, recoil atoms, or protons, comprising a detector in which an ionization current is initiated by the radiation and is caused to raise the potential of the control electrode in a three electrode discharge device, viz. the recorder, to such an extent that a current flows in the anode circuit. the detector is a gas electric discharge device having two or more electrodes, e.g. of nickel or iron, and containing gas or vapour under suitable conditions of pressure and temperature, e.g. neon under a pressure of 5 to 10 mm. of mercury, so that with an inter-electrode potential of 200 to 350 volts, the initial ionization due to the radiation will be multiplied by ionization by collision. The recorder, which may be a " thyratron," is such that with a suitable positive potential, e.g. 100 to 300 volts, for the anode and a suitable negative potential for the control electrode no current or only a minute current passes in the anode circuit and with an increase, even momentarily, of the control electrode potential an anode current passes and continues irrespectively of the potentials applied to the control electrode. As shown, the detector 2 has a glass envelope with one or more mica windows 3. Alternatively, the envelope may be of a material through which the radiations can pass. A metal screen may be placed within or without the envelope or may form part of the envelope. The electrodes 5, 6 which may be parallel rectangular grids or coaxial cylinders are connected respectively to the control electrode 7 and anode 15 of the recorder 8. The electrode 7 is connected through resistance or choke 9 and biassing battery 10 to the heated cathode 11 and the latter is connected to the anode 15 through battery 13, switch 21, and electromagnet 16. In use an alpha-particle for example gives rise to an ionization current in the detector 2 causing the control electrode potential to change and release the anode current in the recorder. The potential of the anode 15 and therefore of the detector electrode 6 thereupon falls to about + 15 volts causing the ionization current to cease and restoring the detector to its initial condition. The anode current energizes the electromagnet 16 and rocks the spring loaded armature 17 which first moves the counter 20 and then opens the contacts 21 breaking the anode circuit. The armature 17 is then returned by the spring 18 and the recorder 8 resumes its initial state. In a modification in which different sources of potential are used for the detector and recorder, the electrode 6 is connected to the anode 15 through a condenser and to the cathode 11 through a resistance or choke and a separate battery. Alternatively, the latter battery may include the battery 13 in series. In a further modification, an auxiliary battery is included in the leads from the electrodes 5 or 6. An alternative method of interrupting the recorder anode current consists in inserting in the anode circuit a condenser and resistance or choke in parallel. The required radiation may be produced within the detector by enclosing polonium or by the action on suitable matter within the detector of gamma-rays, cosmic rays &c.