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THE RELATIVE DIFFERENTIAL CROSS SECTION FOR THE EXCITATION OF THE SINGLET-3P (M(L) = 0) STATE IN HELIUM BY 70 EV ELECTRONS
Abstract
This thesis describes an experiment that measures a relative differential cross section for the excitation of the 3('1)P (m(,l) = 0) state in helium by 70.0 eV electrons. Since this magnetic substrate is degenerate in energy with the other magnetic substates with m(,l) = +1 and -1, it is not possible to measure these differential cross sections from an energy loss experiment. However, it is possible to measure these differential cross sections by detecting an inelastically scattered electron in coincidence with the photon that is emitted when a magnetic substate decays. A ratio (lamda) of the differential cross section for the m(,l) = 0 substate to a sum of differential cross sections for all the magnetic substates can be found from the polarization of the photon or by varying the position of the photon detector. It is also possible to measure the differential cross section for the m(,l) = 0 substate alone by placing the photon detector at a right angle to the electron beam and in the scattering plane which was done here. Therefore, the results of this experiment are fine in detail, in the sense that the differential cross sections are for a state where all the quantum numbers are given. The results of this experiment agree well with previous experimental results, but are now extended to larger scattering angles where the theories give different results. The present results agree best with theories which include electron exchange effects. However, the present results are still below these theories. This may indicate that electron exchange effects are more prominent than expected or that the distortion of the incident electron wavefunction is not what some of these theories have assumed. Part of this thesis deals with some problems that were encountered when the experiment was designed. Some of these problems are: space-charge effects in electrostatic lenses, design of the electron optics for an energy monochromator, and an expression for the effective scattering length. Other subjects such as the Hertzog correction, the Abbie-Helmholtz Law, and apertures are also presented.
Subject Area
Atomic physics
Recommended Citation
HUMMER, CHARLES RAY, "THE RELATIVE DIFFERENTIAL CROSS SECTION FOR THE EXCITATION OF THE SINGLET-3P (M(L) = 0) STATE IN HELIUM BY 70 EV ELECTRONS" (1983). ETD collection for University of Nebraska-Lincoln. AAI8404832.
https://digitalcommons.unl.edu/dissertations/AAI8404832