We investigate the polarization dependence of photoemission from polycrystalline CsI under excitation by linearly polarized 2.69-keV x rays. We measure the electron pulse yield as a function of polarization state for grazing incidence angles between 5°and 18°. No dependence on the incident polarization is found. We find an upper limit of 1.1%, at the 99.99% statistical confidence level, on the fractional change in the pulse yield. Allowing for worst-case systematic uncertainties, we place an upper bound of 3.6% on the difference in the secondary electron pulse yield between the two polarization states.
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