An Optical Method for Analysing Photographs of α—Ray Tracks

Abstract

MR. L. F. CURTISS, writing in NATURE of April 6, describes a method for examining stereoscopic photographs of α-ray tracks taken by two cameras at right angles. The method which we have been using for some years for the measurement of the lengths and initial directions of emission of β—ray tracks (originally suggested to us by Prof. C. T. R. Wilson) depends on the same essential principle as that described by Mr. Curtiss, and our experience confirms his observation of its accuracy and convenience. We described the method in a paper on “The Ranges of Secondary β—rays” (Phil. Mag., 2, p. 1110; 1926) as follows: “The lengths of the tracks were obtained from the stereoscopic photographs by replacing the photographic plates in the cameras, illuminating them and tracing out the common image which coincides in space with the original track”. We have also used the same method in an examination of the initial directions of emission of photoelectron tracks (Proc. Roy. Soc., A, 121, p. 6l2; 1928). In the case of observations with β—rays, since the track is not in one plane, the use of the translucent screen (as described by Mr. Curtiss for α—rays) is not applicable.