For the high-precision measurements in the experiments at the new Mainz Energy recovering
Superconducting Accelerator (MESA), it is necessary to know exactly the long-term spin properties
of the electron beam. For this purpose, a test setup has been built at the Institute for Nuclear physics.
Comparison is made between two processes for activation of a photocathode using oxygen and
nitrogen trifluoride.
The aim is to examine the possible advantages of an oxygen-free preparation, especially with
regard to the influence on the evolution of spin polarization during the experiment. The setup and
the first preliminary results are presented here.