Momentum resolution in (e,2e) experiments

The influence of electron spectrometer alignment on the momentum resolution of electron-impact ionisation (e,2e) experiments is quantified. We show that for coplanar measurements with circular detector apertures, the azimuthal spectrometer alignment should be determined with an accuracy of +/- 0.001 rad to optimise the momentum resolution of an (e,2e) apparatus. Using this criterion, we predict an improvement in the (e,2e) momentum resolution of similar to 30% near q = 0 a.u., where quantum-mechanical scattering models predict a minimum in the triple differential cross-section (TDCS) of atomic p states. This result will assist in determining an upper limit on the effects of second order scattering processes that contribute to small momentum transfers. (C) 2002 Elsevier Science B.V. All rights reserved.