beam diameter

in in situ microanalysis
Diameter of the beam between which 68% of the electrons fall. For Gaussian beam shapes this corresponds to the 2\(\sigma \)-value of the intensity distribution of the beam. Measurement can be carried out by scanning a beam across a sufficiently sharp edge and recording the transmitted electrons.
PAC, 1983, 55, 2023. (Nomenclature, symbols and units recommended for in situ microanalysis (Provisional)) on page 2027 [Terms] [Paper]