Ratio of the Effective Clharge of He Beams Traversing Gaseous and Metallic Cadmium.

Abstract

By successively measuring the energy degradation of He and H beams of the same velocity in the same Cd foil and in the same Cd-vapor absorber at ~ 160 μ pressure, ratios of the stopping power ion He to the stopping power for H at the same velocity (h/fu) and accurate to ~ 1.3% were obtained. These extend from beam velocities of 1.2 to 3.0 in units of e/h; in He kinetic energies from 148 to 920 keV, and cover the region in which the square of the effective charge of the beam is changing most rapidly due to electron capture and loss. Comparison of these ert./en ratios in the attenuated gas and in the metal should indicate whether the effective number of electrons attached to the He nucleus in the gas remain attenuated to it as it traverses the metal. The changes found are fractionally much smaller than those found by Lassen in fission fragments, and Koll and Steigert in fluorine ions. for He ions between 575- and 920-keV energy, the effective charge in the gas seems higher than in the solid, constituting a reversal of the anticipated effect. Empirically, a knowledge of n ./ 'u ratios is useful for the conversion of data on absolute stopping powers for H into He and vice versa. In the kinetic energy range above 1 MeV per amu, Roll and Steigert and I.assen have found that such ratios for fluorine ions, for instance, fall into two groups characteristic of solids as a class and gases and a class. Comparison of the results reported here with n ir /fn ratios obtained by combining results of various experimenters indicates that such a division is not indicated for m ./« u at lower energies per amu, but that the difference between solids and gases in comparable to the differences between different metals and different gases.