  The radiative electron capture (REC) into the K shell of bare Xe ions
colliding with a hydrogen gas target has been investigated. In this study, the
degree of linear polarization of the K-REC radiation was measured and compared
with rigorous relativistic calculations as well as with the previous results
recorded for U$^{92+}$. Owing to the improved detector technology a significant
gain in precision of the present polarization measurement is achieved compared
to the previously published results. The obtained data confirms that for
medium-Z ions such as Xe the REC process is a source of highly polarized x-rays
which can easily be tuned with respect to the degree of linear polarization and
the photon energy. We argue, in particular, that for relatively low energies
the photons emitted under large angles are almost fully linear polarized.
