A systematic optimization of the components of our polarized electron
source has markedly improved its long term stability over earlier vers
ions. The major factors shortening the lifetime of the source have bee
n identified, The essential pans of the spin polarized electron sourer
, such as the vacuum system, crystal holder, cleaving mechanism, caesi
um dispenser, oxygen admittance tube, and computer control activation
features are discussed. The lifetime of the source now exceeds 500 h w
ith a constant polarization of 28.5%. (C) 1997 American Institute of P
hysics.