GB716221A - Improvements in and relating to apparatus for integrating measurement of x-rays or radioactive rays - Google Patents

Abstract

716,221. Cold-cathode tubes. CIVILFORSVARSSTYRELSEN. June 26,1952 [June 30, 1951], No. 16110/52. Class 39(1) [Also in Groups XXXVI and XL(b)] In an apparatus for integrating measurement of X-rays or radioactive rays, of the type having an ionization chamber comprising two electrodes and an auxiliary condenser connected in parallel with the condenser formed by the electrodes, the dielectric in the auxiliary condenser is formed by two or more superposed layers of insulating material to increase the time constant. The apparatus shown comprises a cylindrical case 1 of conductive material, preferably aluminium or an aluminium, alloy or of material carrying an electrically conductive layer, the case or the conductive layer forming one electrode. The other electrode 4 which may consist of aluminium is enclosed by a wound condenser 5 supported in the case 1 by a metallic ring 6 which may be split longitudinally in two halves, the unit so formed dividing the tube into two ionization chambers 3 and 2 bounded by cupshaped members 7 and 8 of graphitized plastic material. The condenser 5 comprises two metal foils separated by two or more layers of an insulating material such as polystyrol, polyethylene, or polytetrafluorethylene having a high specific resistance. A contact member 10 having a disc-shaped head 12 with a projecting tag 13 is slidably mounted in a greased insulating disc 11 and projects through an aperture 9 in the member 7. A disc 14 for example of rubber is mounted on the head 12 and is urged by a spring 15 to close an opening 16 in the case 1. When the apparatus is to be charged or read the member 10 is brought into contact with the electrode 4 by pressure on the disc 14 and a specially designed electrode is inserted through the opening 16 to make contact with the tag 13. Unintentional movement of the contact member 10 may be guarded against by insulating parts provided for example on the. disc 11 which prevent longitudinal movement of the member 10 until it has first been turned through a certain angle. Alternatively the case 1 may be completely closed and a contact device employed which is operated by magnetic means from outside the case. A modified apparatus having a reduced measuring range to enable very small irradiation doses to be registered is provided by lengthening the case 1 and members 7 and 8 to provide a larger air volume and providing an elongation at both ends of the electrode 4. As alternatives to the construction shown, the case may be spherical or lens-shaped and instead of using the dielectric of the condenser 5 to insulate the electrode 4 from the case 1, insulating parts in the form of a hub with spokes may support the electrode 4 which may be a wire, and the condenser 5 may then be a separate unit in the chamber 2 and may be of parallel plate construction. As a further alternative the structure comprising the contact member 10, discs 11 and 14 and spring 15 may be omitted and a simple apparatus constructed which may be so cheap as to be expendible after one operation. Thus, a condenser may be mounted, for example by cold shrinking, between two narrowings in a cylindrical aluminium case with one electrode connected to the case and the other projecting into the ionization chamber formed by the free part of the case, which is closed with a lid, made moisture tight by rubber packings, or by a rubber stopper covered by an aluminium cap which can be removed to gain access to the internal electrode, or if the case or cap is expendible can be punctured by a measuring electrode in the form of a pointed metal rod covered except at the point with insulating material. To provide additional resistance to shocks the aluminium case may be enclosed in a container closed by a lid or cap which may consist of a caoutchouc diaphragm and a cap like a crown-cork, or the aluminium case may be enclosed in a glass envelope sealed by fusing, which must be broken to gain access to the electrodes.