Comparative tests of conventional and retarding-potential Mott polarimeters

The performance of a spherical field-free and a conical retarding-potential Mott polarimeter is compared. The stability of the detector signal with respect to a change in the position of the incoming electron beam is studied for two different primary electron beam energies. Shifting the incoming electron beam by 0.6 mm does not change the counting rate in the spherical field-free detector but induces a 7% or 18% change in the conical retarding-potential detector when using 1600 and 500 eV electrons, respectively. This may result in an error of the measured electron spin polarization. (C) 2001 American Institute of Physics.