The Ionization of Argon and Neon by Neutral Argon Beams.

As a result of the discovery of Kallmann and Rosent"2 that the probability of charge transfer is very great for gas ions moving in a gas of their own molecular or atomic species, the possibility of obtaining an atomic beam of high intensity is at once indicated. Since the charge transfer itself takes place without altering the translatory energy of the moving ion, the translatory energy of the formed neutrals will equal that of the ions in case the ion is not scattered, or only slightly scattered. This fact has been utilized to produce beams of neutral argon atoms for the purpose of this investigation. The apparatus consists of 3 parts. In part I argon ions are formed by electron impact. These argon ions pass through an aperture in a diaphragm of part I and are accelerated between parts I and II by means of a field to give them the desired velocity. By means of an aperture in a diaphragm in part II they pass through the field-free chamber of part II in which argon gas is maintained at a suitable pressure. Between parts I and II the space is evacuated by a high speed pump. In space II the argon ions encounter atoms of argon and neutralize themselves by *transfer of charge. From part II the neutral argon beam passes by means of a diaphragm and an aperture into an evacuated space in which a strong retarding field allows only the neutral atoms to pass through a diaphragm into space III. Electrons which might be formed between parts II and III are deflected away by an appropriate transverse field. Thus only neutral atoms of known velocity enter part III.3 This part constitutes the ionization chamber in which the interaction of the argon beams with argon and neon is investigated at a suitable gas pressure. In the case of both gases used an exceptionally intense ionization was observed in part III. Both the positive and negative saturation currents were measured. Saturation was obtained in both cases for potentials of-4 volts between electrodes in space III lying parallel to the beam and protected by a sort of guard ring from secondary electrons. No measurement of the intensity of the primary atomic beam was undertaken in these preliminary experiments.