A Physical Investigation of the Radiation from a Low-voltage X-ray Tube (Cautery Technique)

Abstract

A study has been made of the physical properties of the radiation produced at 44 kV by the “Metalix” therapy apparatus. Absorption measurements in aluminium, water, and certain other solutions are described. The first half-value layer of the unfiltered radiation is found to be 0·30 mm. Al, corresponding to an equivalent wavelength of 840 X.U. Central axis depth-dose curves for the unfiltered and filtered radiation at various focal-skin distances are given, together with some complete isodose curves. A condenser chamber for the measurement of the dosage-rate in air which may be used with standard Victoreen condenser dosemeter is described. A surface dosage rate of 7,610 r/min. is obtained with the unfiltered radiation at the shortest focal-skin distance (2·0 cm.), but the penetration is very small, 4 mm. of water being sufficient to reduce the dosage-rate to one half of its surface value. Owing to the heavy absorption of the water the amount of scattered radiation outside the geometrical edge of the beam is small. Measurements of the stray radiation around the tube are described. The results of other workers are discussed, and, finally, a description is given of an attempt to determine the energy distribution in the spectrum of the radiation by an analysis of the absorption curve in aluminium.