Cloud-Chamber Studies of Electronic and Nuclear Stopping of Fission Fragments in Different Gases

Abstract

The range of fission fragments in different gases has been studied by means of the cloud-chamber method. The reduced range was found to increase from xenon to helium, and the range in helium was found to be about 18 percent larger than in argon, which is in agreement with previous determinations. The reduced range in hydrogen was found to be smaller than in other gases, pointing to a comparatively larger electronic stopping effect. The reduced ranges of fragments passing through hydrogen and deuterium, respectively, have been compared and the range in deuterium was found to be about 6 percent larger than that in hydrogen. Since the electronic stopping effect is identical in both gases, the difference in the ranges must be ascribed to the nuclear stopping effect. The spread of the range within the groups was discussed in relation to the energy measurements by Flammersfeld, Jensen, and Gentner, using Bohr's theory of the stopping effect, and a reasonable agreement was obtained. The previous conclusions concerning the velocity-range relations of fission fragments were confirmed by new, more direct evidence, using close collisions for a determination of the velocity or mass of the fragments.