Electron-atom scattering total cross sections

As an example of the energy dependence of the total cross section for positron-atom scattering, a schematic of the data for helium atoms is shown in Figure 2.1, together with the corresponding data for electrons. It is seen that [Pg.41]

Fig. 2.18. Positron-atomic hydrogen and electron-atomic hydrogen total scattering cross sections. Experiment , positrons o, electrons both sets of data...

Stein, T.S. and Zhou, S. (1993). Toward measurements of total cross sections for positrons and electrons scattered by potassium and rubidium atoms. Phys. Rev. A 47 1535-1538. 

There has been a predecessor to the Bennewitz-experiment Berkling et al. (1962) have measured the total cross section for collisions between oriented 2P3/2 Ga atoms with noble gas molecules. This experiment was never taken up again although there is a whole group of atoms with anisotropic electronic structure which can be likewise oriented. The information which can be obtained from scattering experiments with oriented atoms is essentially the same as with oriented molecules. 

Neutrons are scattered isotropically from individual nuclei, whereas, for LS and SAXS, the scattering originates in the electron cloud, so the atomic form factors are in principle (2-dependent. However, the variation is small in practice (<1% for Q < 0.1 A ) and is usually neglected for SAXS and LS [36]. The Thompson-scattering amplitude of a classical electron is rj = 0.282 x 10 cm [65], so the X-ray scattering length of an atom, /, is proportional to the atomic number (/ = rjZ) and increases with the number of electrons per atom. For neutrons, values of b vary from isotope to isotope (see below). If the nucleus has nonzero spin, it can interact with the neutron spin, and the total cross section (atot) splits into coherent and incoherent components as explained below. 

Fig. 2.6. The oven, which also served as the scattering cell, used by the Detroit group for studies of positron-alkali atom and electron-alkali atom total scattering cross sections. The open circles indicate thermocouples.

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