Open AccessA simple radioactive method for the photographic measurement of the integrated intensity of X-ray spectra
Author(s) -
W. T. Astbury
Publication year - 1927
Publication title -
proceedings of the royal society of london. series a, containing papers of a mathematical and physical character
Language(s) - English
Resource type - Journals
eISSN - 2053-9150
pISSN - 0950-1207
DOI - 10.1098/rspa.1927.0115
Subject(s) - intensity (physics) , optics , spectrometer , light intensity , photographic plate , materials science , aqueous solution , ray , x ray , chemistry , physics
In this paper will be given a preliminary account of a method by which the intensity distribution in X-ray crystal photographs may be estimated by means of a simple and inexpensive apparatus. In the usual photometric procedure the blackening of a photographic plate is estimated by finding the intensity of light transmitted through it. In the method to be described the photographic plate is replaced by a carbon print, and the light and light-sensitive cell byα -rays and a simpleα -ray electroscope respectively. The obvious advantages of such a system are, of course, ease of construction and negligible cost; but, as will be seen below, there already appears promise of a much more weighty advantage, namely, that with suitable adjustment the apparatus may be made tointegrate the X-ray intensity of a crystal reflection after the manner of the Bragg ionisation-spectrometer. Details are given below, but briefly the method is as follows. A carbon print is first made of the photographicnegative . A carbon paper (or tissue, as it is called) consists merely of a pigmented film of gelatine sensitised with dilute aqueous potassium dichromate solution. On exposure to light such a film becomes insoluble, the depth of the insoluble layer after a given time being a measure of the intensity of the incident light. On development with warm water the remaining soluble portions are washed away, and there is left a film of thickness which varies according to the variation in blackness of the original negative. This insoluble film being very tough is readily detached, and, because it is so thin, its stopping-power forα -rays is just about of the right order. The variations in its thickness are thus very easily followed by aid of a few square millimetres of foil on which polonium has been deposited, a single slit, and theα -ray electroscope described by C. T. R. Wilson, which is usually figured in text-books. The latter can be constructed from an ordinary cigarette tin, and a simple tele-microscope with eyepiece scale.