The Scattering of low Speed Electrons by Platinum and Magnesium

Abstract

Scattering of electrons by platinum and magnesium.—Electrons from a tungsten filament were accelerated with voltages up to 1000, and a restricted beam was directed against a platinum target at 45° incidence. The number of scattered electrons with over 9/10 the energy of the primaries was determined for various directions by measuring the current to a Faraday box collector which could be revolved so as to explore the range from within 15° of the primary beam ($\Psi ={15}^{\circ }$) to the plane of the target ($\Psi ={135}^{\circ }$). For bombarding potentials up to 200 volts the intensity of scattering decreases more or less regularly from low to high values of $\Psi$, indicating a maximum for $\Psi =0\mathrm{}$. At higher potentials the scattering pattern develops two well marked lobes besides the one for $\Psi =0\mathrm{}$. When the platinum target was covered with a deposit of magnesium the patterns found are simple with the exception of a small lobe on the curves for potentials less than 150 volts. Up to 500 volts the maximum intensity is apparently in the direction $\Psi =0\mathrm{}$, but for higher voltages the direction shifts to around $\Psi ={90}^{\circ }$. Theoretical interpretation. Since low speed electrons are more easily deflected than $\alpha$-particles, their scattering patterns depend not only on the field immediately about the nucleus but also upon its nature in regions beyond various or all of the structural electrons. The complicated patterns for platinum are taken to indicate that the field out from the nucleus in the platinum atom is characterized by several approximate discontinuities resulting from more or less definite concentrations (shells) of electrons at certain distances from the center. The magnesium atom having a single strong concentration of electrons (the L group) gives rise to simple patterns.