No abstract

Ionospheric electrons of the D-region were investigated by means of cylindrical Langmuir probes. It was found that the energy dist¡ and the density of the eleetrons are affected by the presence of negative ions of ionospheric origin and by the high energetie protons whieh cause ah auroral aetivity at aretie latitudes. A measurable differenee is detected between the electron temperature and the neutral gas temperature at D-region altitudes. The fast protons of the aurora are believed to be the o¡ of the parfial heating.

Monte Carlo calculations have been performed using MCNP code to study the generation, angular distribution and energy spectrum of photo-neutrons for 1 GeV and 150 MeV electron beam energies impinging on different thickness of Tungsten, Tantalum and Lead targets. It is noticed that the photoneutron yield increases as the target thickness increases, then saturates beyond an optimized thickness of the target. Moreover, the photo-neutron yield shows a significant increase as the electron energy increases. At the optimized thickness, the angular distribution of photo-neutrons is found almost isotropic for 150 MeV electrons and anisotropic for 1 GeV electrons. Furthermore, by increasing the electron energy and/or the target thickness, the angular distribution is found to be forward peaked. The energy spectrum of photo-neutrons can be well described by a Maxwellian distribution for both electron energies. Such calculations can help in developing a photo-neutron source-based time of flight facility (TOF) for elemental and isotopic identification via neutron resonance spectroscopy. Photo-neutron yields, angular distribution, mean energy, energy spectrum and nuclear temperature for 1 GeV and 150 MeV electron energies and different target materials are presented.

An investigation of the collection of current of different eharged particles by a moving cylindrical probe is outlined. The required volt--ampere relations ate derived for the case when the probe potential retards both electrons and negative ions. The theoretical work is extended to the case of a plasma with a superimposed drift when positive ions are retarded by a positive probe potential. It has been proved that the collectcd ion current depends strongly on the drift velocity and on the angle between the axis of the probe and the velocity rector.In general, the cylindrical Langmuir probes proved to be a good tool in studying ionospheric ion mass spectra and temperature together with electron temperature since they avoid most of the difficulties incurred in using any other form of probes.In the same time, the derived relations could be extended to study the energy distribution function for any species of charged particles.