GB615562A - Improvements in or relating to means for measuring or detecting x-rays or the like radiation - Google Patents

Abstract

615,562. X-Ray measurements. GENERAL ELECTRIC CO., Ltd., DUNHAM, C. R., and MICHAELIS, W. M. May 1, 1946, No. 13158. [Class 37] [Also in Group XX] Means for measuring or detecting X-rays or like radiation comprises an ionisation chamber having a pair of electrodes and means to produce an alternating or pulsating ionisation current within the chamber, the amplitude of the current being dependent on the intensity of the radiation falling on the chamber. As shown, the ionisation chamber comprises an outer electrode 4 of e.g. graphite closed by an amber plug 5 supporting an inner electrode 3 and coated with metal 6 to contact the electrode 4. A constant D.C. potential is applied to the electrodes through leads 7, 8 from a cable 9. A steel cylinder 2 mounted to rotate on a ball bearing 13 on the amber plug 5 is rotated by air from a nozzle 15 impinging on a turbine wheel 14 mounted on the cylinder. Radiation passes through diametrically opposite windows 16, 17 each extending over a 90 degrees sector of the cylinder 2. The periodical exposure of the chamber to radiation produces a pulsating ionisation current, the A.C. components of which are readily amplified and measured. Alternatively, the apertured wall may be stationary and have a shutter, which may, according to the Provisional Specification, be a cylinder with part of its surface cut away, rotating round the wall. An A.C. ionisation current may be produced by applying an alternating potential to the electrodes of an ionisation chamber. Two chambers may form opposite arms of an A.C. bridge network, the other two arms being formed by similar chambers shielded from or out of the field of the radiation, or evacuated, or by condensers having the same capacity as the chambers. The change in bridge current is measured and the bridge may be balanced initially to give zero current for zero radiation.