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Mott Scattering Measurements of the Spin Polarization of the NBS GaAs Electron Source



Jabez J. McClelland, B Waclawski


Measurements of the spin polarization of the GaAs electron source were carried out on the atom beam apparatus in the Electron Physics Group at the National Bureau of Standards. Both a cylindrical Mott analyzer operating at 100kV ("Maximott") and a hemispherical Mott analyzer operating at 30 kV ("Minimott") were used. A calibratoin of the Minimott was carried out and compared with that of the Rice group. The following conclusions were arrive at: 1) In December of 1986, the atom beam GaAs source had a polarization Pe of 0.2435 plus or minus} 0.0074. 2) Over a period of a year, from December 1985 to December 1986, the polarization fell by somewhere between 6 and 24% of its original value. 3) Our calibration of the Minimott led to values of Seff, the effective Sherman function, consistently lower than the Rice values, though there was marginal agreement considering the error estimates. 4) Conclusions (3) is based on an absolute value for Sgold of 0.39 at 100kV, 120° scattering angle, as used by the Rice group. This a theoretical value, which has not been experimentally confirmed. Double scattering experiments have yielded a value for Sgold of 0.370 plus or minus} 0.008. This value for Sgold was used to determine the absolute source polarization. 5) Taking into consideration the lack of knowledge of Sgold, the most conservative uncertainty estimate for Pe is plus or minus}0.015.
Electron Physics Group Internal Report


McClelland, J. and Waclawski, B. (1987), Mott Scattering Measurements of the Spin Polarization of the NBS GaAs Electron Source, Electron Physics Group Internal Report, [online], (Accessed April 20, 2024)
Created April 5, 1987, Updated October 12, 2021