Angular Dependence of the Scattering of Metastable Helium Atoms in Helium and Neon

Abstract: Abbreviated introduction: This dissertation concerns the measurement of collision cross sections for the scattering of excited helium atoms in helium and neon as a function of the minimum angular resolution of the beam apparatus. Some of the helium atoms in gaseous helium are excited to both the 21S and 23S metastable states.

An atomic beam of the helium atoms is then produced and allowed to enter a collision chamber in which a gas is introduced at low pressure (ca. 10-3 mm). The scattering of the metastable helium atoms in the beam is observed by measuring the electron current ejected by the excited atoms when they arrive at metal detector surfaces. Both elastic and inelastic collisions of the excited atoms take place. Since the method of detection is insensitive to particles in the ground state, there is no inter- ference from the normal atoms in the beam. Because of the two metastable atoms formed, a knowledge of the beam composition is necessary if one is to determine the individual cross sections.

The beam composition has been determined by passing the beam Through an inhomogeneous magnetic field.

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