Scattering of high velocity electrons by thin foils

With a narrow, homogeneous beam of electrons, scattering by thin foils of aluminum, silver and gold has been investigated. Voltages up to 145 kv (β=0.63) were used. Under conditions where single scattering was predominate and secondary electrons were absent, the amount of scattering was studied as a function of the primary energy, atomic number and angle. Absolute values were also obtained. The above investigations have lead to the following results: (1) Secondary electrons are defined and a means of eliminating them is proposed and used. (2) Wentzel's criterion for single scattering is tested over a wide range of energies. The value of θ/4ωmin for aluminum is found to increase from 3.3 at 45 kv to 6.1 at 145 kv. (3) A more critical criterion for single scattering by thin foils is obtained which depends on the shape of the curve connecting ρ, the amount of scattering, with angle. (4) Dependence of scattering on energy of primary beam is found to agree well with either Mott's equation or with the relation k/V2, but is at variance with the classical relativistic theory. (5) Comparison of values of scattering for aluminum, silver and gold shows that ρ increases faster than Z squared. (6) Scattering is obtained as a function of angle from 95° to 173°. For aluminum the dependence found experimentally agrees well with either Mott's or Rutherford's equation. The latter also gives the correct dependence on angle for silver and gold. Mott's equation is not applicable for these heavy elements. (7) Absolute values of scattering for aluminum compared with theory give ρ=1.32 of the value given by Mott's equation. This relation is valid within the ranges θ=95∘-173∘, V=56-145 kv. (8) Secondary electrons coming from the foil are distributed according to the simple cosine law. (9) No evidence of loss of energy due to radiation is found up to one-half the energy of the primary beam

Energetic particle influence on the Earth's atmosphere

This manuscript gives an up-to-date and comprehensive overview of the effects of energetic particle precipitation (EPP) onto the whole atmosphere, from the lower thermosphere/mesosphere through the stratosphere and troposphere, to the surface. The paper summarizes the different sources and energies of particles, principally galactic cosmic rays (GCRs), solar energetic particles (SEPs) and energetic electron precipitation (EEP). All the proposed mechanisms by which EPP can affect the atmosphere are discussed, including chemical changes in the upper atmosphere and lower thermosphere, chemistry-dynamics feedbacks, the global electric circuit and cloud formation. The role of energetic particles in Earth’s atmosphere is a multi-disciplinary problem that requires expertise from a range of scientific backgrounds. To assist with this synergy, summary tables are provided, which are intended to evaluate the level of current knowledge of the effects of energetic particles on processes in the entire atmosphere

Dynamics of the Earth's particle radiation environment

The physical processes affecting the dynamics of the Earth's particle radiation environment are reviewed along with scientific and engineering models developed for its description. The emphasis is on models that are either operational engineering models or models presently under development for this purpose. Three components of the radiation environment, i.e., galactic cosmic rays (GCRs), solar energetic particles (SEPs) and trapped radiation, are considered separately. In the case of SEP models, we make a distinction between statistical flux/fluence models and those aimed at forecasting events. Models of the effects of particle radiation on the atmosphere are also reviewed. Further, we summarize the main features of the models and discuss the main outstanding issues concerning the models and their possible use in operational space weather forecasting. We emphasize the need for continuing the development of physics-based models of the Earth's particle radiation environment, and their validation with observational data, until the models are ready to be used for nowcasting and/or forecasting the dynamics of the environment