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Absolute differential cross sections for elastic scattering of electrons over small angles from noble-gas atoms

1986; IOP Publishing; Volume: 19; Issue: 19 Linguagem: Inglês

10.1088/0022-3700/19/19/024

1747-3721

René W. Wagenaar, A. de Boer, T van Tubergen, J. Los, F J de Heer,

X-ray Spectroscopy and Fluorescence Analysis

Experimental absolute differential cross sections are presented for elastic scattering of 20-200 eV electrons from the noble gases, with an angular resolution better than 0.25 degrees . A novel type of parallel-plate electrostatic energy analyser is used for the simultaneous determination of the angular distribution of the scattered particles. The use of microchannel plates and a multichannel detection technique yields an improvement in measuring efficiency of at least two orders of magnitude compared with the traditional angular-scan technique. The accumulated signals have been made absolute to within 7% by carefully determining all the relevant parameters such as primary-beam intensity, gas density and collision length, analyser transmission and channel plate efficiency. A comparison is made between the present results and those from various existing theoretical models. The best agreement was found with the R-matrix calculations of Fon et al. (1984). A hitherto unknown structure in helium was revealed when the impact energy was scanned in a narrow range around the threshold for ionisation.