The use of impact linear polarization of chromospheric lines as a diagnostic of 100 keV protons is proposed. Observations of hard X-ray emission are examined, noting the possibility that 100 keV proton beams bombarding the atmosphere could create a hot thermal plasma at the origin of X-ray emission. The application of impact linear line polarization as a diagnostic of the existence of energetic particles with anisotropic velocity distribution functions is described. The mechanisms leading to an anisotropic proton distribution in the solar chromosphere are discussed and the required initial energy and energy flux for accelerated protons in the corona are derived. It is suggested that it is possible to infer the original proton anisotropy in the corona and the effect of this anisotropy on the proton energy and proton energy flux required to reach the H-alpha-forming layers. 28 refs.