GB690159A - Improvements relating to radiation detectors - Google Patents

Abstract

690,159. Electrometers. METROPOLITANVICKERS ELECTRICAL CO., Ltd. Oct. 23, 1951 [Oct. 31, 1950], No. 24741/51. Class 37. [Also in Group XL (b)] Apparatus for detecting radio-activity comprises a moving vane electrometer situated in an ionization chamber and a piezo-crystal under pressure, the potential developed across this crystal being applied to the fixed and moving plates of the electrometer so as to give it an initial deflection which is gradually reduced as the gas in the chamber is ionized by radio-activity. As shown, the instrument comprises a cylindrical plastic envelope 1 coated internally with a conducting layer such as " Aquadag " (Registered Trade Mark). The top of the chamber is closed by a diaphragm 3 carrying a central cylinder 4 with an insulating bush 7 in its bottom, through which passes an extension 8 of a table 10. The piezo-crystal, which is of barium titanate with metal coated faces, rests on this table, and the crystal is compressed between the table and a thumb-screw 6. The electrometer consists of a bracket 12 carrying insulating bushings through which pass metallic supports carrying flat springs 17, 18 between which is mounted the moving vane suspension 25. The moving vane 24 (Fig. 2), rotates between pairs of fixed vanes 20, 21 and 22, 23 which are supported by a ring 19 attached to bracket 12. The very light pointer 27 carries a mica button at one end as an indicator and a counterweight at the other. In use, diaphragm 3 is pressed down until extension 8 contacts the metal support 15 when the voltage developed across the piezo-crystal is applied across the moving and fixed vanes of the electrometer. Pressure on the crystal is then increased by means of the thumb-screw until pointer 27 reads zero. By changing the volume of the ionization chamber or the electrical capacity of the instrument the full scale value of the instrument may be varied.