Electron-impact excitation of the Hg*(63P1) state has been studied by means of electron-photon coincidences involving polarized electrons. Differential Stokes parameters (photon polarization components) have been determined for scattering angles ranging from 10 to 90' at E=8 eV and from 10 to 60' at E=15 eV. The state multipole formalism has been used to extract the charge-cloud distribution of the Hg*(63P1) state from the measured Stokes parameters at E=8 eV. At this energy shape and size of the charge-cloud distribution depend strongly on the direction of the electron polarization vector. The experimental data at E=8 eV are compared with R-matrix calculations where good agreement is obtained.
The conventional methods of determining the analyzing power of a Mott detector for electron-polarization measurement are not very accurate. That is why alternative methods have recently been discussed. The present paper shows how a Mott detector can be calibrated with an uncertainty of ±1% using the circular polarization of impact radiation from helium atoms that are excited by polarized electrons. The retarding-field-type Mott analyzer, its performance, and the calibration procedure are described in detail. Accurate data of the circular light polarization that may be used for absolute electron polarimetry are given at electron energies of 23.3 and 26 eV.
Spin effects for electron-impact excitation of Hg(63P,) have been studied for small scattering angles (e,s30") and energies of 15, 30 and 50 eV. In an electron-photon coincidence experiment the linear polarisation components P, and P, (for photon emission angles perpendicular and parallel to the scattering plane, respectively) have been measured from which the relative spin-flip cross section poo could be determined. It has been found however, that reliable results are obtained only if various corrections, which have not been discussed in previous investigations, are taken into account. With these corrections the data agree well with predictions of widely accepted theoretical models. As an example, this is demonstrated by comparing the experimental data with a DWBA calculation. In particular poo is zero with the experimental accuracy for small scattering angles (Oc< IO") at E = 50 eV.
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