THE LINEAR-POLARIZATION STOKES PARAMETER P-1 FOR THE 3(1)D STATE OF HELIUM EXCITED BY 40 EV ELECTRON-IMPACT

The linear polarization Stokes parameter P-1 for electron impact excit ation of the 3'D state of helium is investigated following a recent pu blication by Wedding et al in which values reported at small scatterin g angles at 40 eV incident electron energy strongly disagree with earl ier measurements of Beijers et al and Donnelly and Crowe. The earlier data are confirmed by new measurements. Only a multichannel eikonal ca lculation gives even qualitative agreement with the experimental data. It is shown that the data of Wedding et al are consistent with a norm alization error. Their method of simultaneous determination of three S tokes parameters is shown to lack sensitivity to substantial changes i n the Stokes parameters and is inappropriate for data with their stati stical quality.