GB546095A - Apparatus for measuring the quality and quantity of x-radiation - Google Patents

Abstract

546,095. Measuring quality and dosage of Rontgen-rays. HERZ, R. H. Feb. 17, 1941, No. 2179. [Class 98 (i)] [Also in Group XXXVI] In apparatus for measuring the quality of X- radiation, a cathode-ray tube is used having a calibrated screen on which are indicated values corresponding to the ratio of the intensities of the radiation before and after passing through a filter. As shown, ionization chambers I<SP>1</SP>, I<SP>2</SP> of similar characteristics are positioned in the path of the rays, a filter F of suitable thickness and material, for example copper or aluminium, being positioned between the tube and the chamber I<SP>2</SP>. Batteries B1, B1<SP>1</SP> supply saturation potentials to the chambers, and the currents produced owing to ionization by the rays set up potentials across high resistances R1, R1<SP>1</SP> in the grid circuits of electrometer valves V1, V1 of high grid impedance. The output of these valves is further amplified by valves V2, V2<SP>1</SP> and is applied to the deflection electrodes A, C and B, D of a cathode-ray tube K. The ratio of the two mutually perpendicular deflections of the beam corresponds to the ratio of the intensities of the filtered and unfiltered radiation and is read on a scale formed by radial lines. The deflection caused by the unfiltered rays is a measure of the intensity of the radiation or of the dosage. For short time and integrating measurements, condensers C1, C2 are connected in parallel with the resistances R1 and R1<SP>1</SP>, the voltages developed then depending on the intensity of radiation and the time during which the condensers are charged. With suitable intensities of radiation and design of ionization chambers the amplifying system may be omitted. Fig. 3 shows two ionization chambers 13, 14 of half frusto-conical shape arranged in the cone P of the X-ray tube, a slot S allowing a filter to be introduced to filter the radiation passing to the chamber 13. With this arrangement the measurements may be made during exposure of a subject. Known condenser type of ionization chambers may be employed, which after charging are partially discharged by exposure respectively to the filtered and the unfiltered radiation, and are then connected to the cathode-ray apparatus to measure the amounts of discharges produced in the two cases. The Provisional Specification describes the use of two photo-electric cells subjected to the light from fluorescent surfaces activated by the filtered and unfiltered X-rays, the outputs from these cells, after or without amplification, being indicated on the screen of a cathode-ray tube as above described. The screens and cells may be arranged in the conical shade of the X-ray tube.