GB730199A - Radio-activity detection - Google Patents

Abstract

730,199. Batteries. OHMART, P. E. June 25, 1952 [June 27, 1951], No. 15945/52. Class 53. [Also in Groups XL (a) and XL (b)] A device for measuring radio-activity utilizes the discovery that electro-chemically dissimilar metals separated by a gas ionized by radioactivity produce an E.M.F. in an external load. The present invention utilizes this discovery to enable the E.M.F. source to be omitted from an ionization chamber detector arrangement. As shown (Fig. 2), the chamber consists of a number of cells in series each comprising a pair of plates such as 7, 12. Plate 7 which may be of lead on brass forms the cap of the chamber. Plate 12, which is of lead di-oxide plated on gold, forms the other plate of the cell. Plate 12 is back-toback with the next lead on brass plate 13 so that all the cells are series-connected, connection being finally made to the lead dioxide on gold plate 20 through an insulated rod 21. The space between the plate is filled with an ionizable gas such as argon, hydrogen, nitrogen or air. In the arrangement of Fig. 3 (not shown), the cylindrical case forms one electrode while a concentric cylinder inside the case forms the other. A cylindrical condenser situated inside the inner electrode and connected to the cell is charged by the cell and the top of the chamber is formed by a flexible diaphragm in which is mounted an insulated pin. The charge accumulated by the condenser may be applied to a ballistic galvanometer by depressing the diaphragm until the pin makes contact with the control electrode. The case may be filled with air or argon at a pressure of three atmospheres. An arrangement comprising a number of cells in parallel is shown in Fig. 4. A number of plates 38-48 are mounted on a central rod 49 with which they are in contact and are interleaved with plates 39 to 47 which are supported by and in contact with the cylindrical housing 35. Odd-numbered electrodes are of brass plated with lead, while even-numbered electrodes are of brass plated with gold. If alpha or beta radiations are to be detected the cup may include a thin window of nylon or rubber hypochloride coated with a very thin coat of the selected electrode material, while the inner electrode may be thin " Formvar " (Registered Trade Mark) coated with the desired electrode material, thin metallic foil, alpha-transparent carbon or magnesium oxide. If the device is required for neutron measurement the outer case may be filled with a hydrogenous material such as polystyrene coated with the electrode material or the case may be of metal internally coated with polystene with a final inside coating of carbon. A filling gas which is itself a source of secondary particles such as hydrogen, boron trifluoride or methane may be used.