How linearly polarized is the X-ray beam from the X-ray generator?

We report the measurement result of the degree to which X-rays from a conventional X-ray generator in the energy range up to 60 keV are linearly polarized. The X-ray generator we used in which the accelerated electrons hit the water-cooled metal head is widely used commercially. We measured the degree of linear polarization by employing a Thomson scattering process. We found that the degree of linear polarization depends only on the ratio between the X-ray energy from 20 keV to 60 keV and the applied voltage to the electron. The higher the ratio is, the higher the degree of linear polarization we obtain, whereas the weaker the X-ray intensity is. By selecting an appropriate combination between the applied voltage and the X-ray energy: we confirmed that we would obtain a mono-energetic highly linear polarized X-ray beam with enough intensity for practical use.