Abstract
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.
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