Inelastic and Elastic Electron Scattering in Argon

Abstract

The energy distribution and the angular distribution of electrons scattered by argon atoms were investigated both for elastically and inelastically scattered electrons. Elastic scattering was investigated over the angular range between 10\ifmmode^\circ\else\textdegree\fi{} and 170\ifmmode^\circ\else\textdegree\fi{}, and for the energy range between 50 and 550 volts. The scattering curves fell off steeply with increasing angle. In the case of the 50 and 100 volt electrons, however, maxima were found at 100\ifmmode^\circ\else\textdegree\fi{} and 90\ifmmode^\circ\else\textdegree\fi{} respectively. The 400 and 550 volt curves when plotted as a function of $\frac{sin(\frac{\ensuremath{\theta}}{2})}{\ensuremath{\lambda}}$ (where $\ensuremath{\theta}$ is the angle and $\ensuremath{\lambda}$ the de Broglie wavelength) were superposable, in agreement with Mott's theory. The number of elastically scattered electrons, integrated over all angles, depends on the colliding energy in much the same way as does the difference between the total electron absorption coefficient and the ionization efficiency. The energy distributions of electrons scattered inelastically in argon at 10\ifmmode^\circ\else\textdegree\fi{} were measured for 50, 100, and 200 volt electrons. It was found that as the energy of the colliding electrons increased the probability of the larger energy losses became relatively greater than the probability of the smaller energy losses. Angular distribution curves (5\ifmmode^\circ\else\textdegree\fi{} to 35\ifmmode^\circ\else\textdegree\fi{}) for such losses (11.6 to 34.0 volts) were steeper the smaller the magnitude of the loss. For any one loss, the steepness increased with the speed of the colliding electron. Electrons which have lost more than half the energy left over after ionization are called ejected electrons. To each ejected electron there corresponds a colliding electron, and the sum of their energies amounts to the original energy before collision less the energy of ionization. The angular distributions of slow ejected electrons having various amounts of energy (1 to 8 volts) were studied for different collision energies (50 to 200 volts). Such distribution curves showed a general distribution of electrons over all angles with, in many cases, strong maxima at large angles (90\ifmmode^\circ\else\textdegree\fi{} to 160\ifmmode^\circ\else\textdegree\fi{}). The positions of the maxima depended in a definite way upon the energy of collision and the energy of the ejected electron.