A. R. Milosavljević

Physics - Thesis - M. Sc. Thesis

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UNIVERSITY OF BELGRADE  FACULTY OF PHYSICS Aleksandar R. Milosavljević Critical minima in elastic scattering of electrons by argon atoms MASTER THESIS  Belgrade, 2004. The work was done under the supervision of Dr. Bratislav Marinkovic. (written in Serbian) ABSTRACT The experimental investigation of critical minima, which are defined by the points where differential cross section (DCS) attains its smallest value as a function of both scattering angle and incident energy, in elastic electron scattering by argon atoms was presented. The measurements were performed as a function of both scattering angle and incident energy. The absolute calibration of the entire data set was obtained via normalization to a single point. Also, the position of high-angle critical minimum versus incident energy were independently extracted by least square fit of the angular distributions to  Legendre polynomials. The measurements were performed in the angular range from 40^o to 130^o, and energy range from 30 eV to 150 eV. A very good agreement with previous results has been obtained. Present measurements are the first detailed experimental investigation of elastic electron-argon scattering in the energy range from 100 eV to 150 eV (i.e. in the vicinity of the high-energy critical minimum). In this energy range, both DCS and high-angle minimum position versus energy are tabulated. Also, both present and previous available positions of critical minima in elastic electron-argon scattering are tabulated. The high-energy critical minimum, which has been only preliminary reported up to present, was found to be at 129.4±0.5 eV and 119.4±0.5 degrees. Also, electron-optical characteristics of the apparatus UGRA have been investigated both experimentally and theoretically. With the use of program SIMION and additional programming the investigation of a number of electron-optical systems (the energy scanning with constant transmission function, angular resolution, focal characteristics, ...) has been performed. Some new results for the four-electrode electrode lenses and double cylindrical mirror analyzer have been presented. USEFUL REFERENCES The high-energy critical minimum in elastic electron scattering by argon, A. R. Milosavljević, S. Telega, D. Šević, J. E. Sienkiewicz and B. P. Marinković, 2004, Eur. Phys. J. D (in press) 2. Elastic electron scattering by argon in the vicinity of the high-energy critical minimum, A. R. Milosavljević, S. Telega, D. Šević, J. E. Sienkiewicz and B. P. Marinković, 2004, Radiat. Phys. Chem. (in press) Cvejanović D and Crowe A 1997 J. Phys. B: At. Mol. Opt. Phys. 30 2873-88 Kessler J, Liedtke J and Lucas C B 1976 Physics of Ionized Gases (Dubrovnik) ed B Navinšek (Ljubljana: J Stefan Institute) p 61-4 Lucas C B 1979 J. Phys. B: Atom. Molec. Phys. 12 1549-58 Panajotović R, Filipović D, Marinković B, Pejčev V, Kurepa M and Vušković L 1997 J. Phys. B: At. Mol. Opt. Phys. 30 5877-94 Sienkiewicz J E, Konopińska V, Telega S and Syty P 2001 J. Phys. B: At. Mol. Opt. Phys. 34 L409-18 Fon W C, Berrington K A, Burke P G and and Hibbert A 1983 J. Phys. B: Atom. Molec. Phys. 16 307-21 SOME RESULTS Angle dependent differential cross sections for elastic electron-argon scattering in the vicinity of the high-energy critical minimum. Energy dependent differential cross sections for elastic electron-argon scattering at several fixed scattering angles.