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We have investigated spin precession mechanisms of polarized slow positrons in materials caused by multiple Coulomb scatterings, Bhabha scatterings and bremsstrahlungs. It is found that the degree of depolarization is strongly dependent on the atomic number of materials, and the depolarizations caused by the Bhabha scatterings and the bremsstrahlungs are negligible compared with those caused by multiple Coulomb scatterings. By incorporating the theoretical formulations of spin precession due to the three processes mentioned above into a Monte-Carlo simulation program, we can successfully describe depolarizations of polarized slow-positron beams in materials, i.e. a target, an absorber, and a moderator which are utilized for slow-positron production facilities. The magnitudes of the polarizations thus estimated are in good agreement with experimental measurements.

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