Parameters of a beam of runaway electrons and X-ray radiation generated in a gas diode at different atmospheric pressures are studied. It is shown that the maximum beam currents and intensities of X-ray radiation are generated at an air pressure of about 102 Pa. Distribution of beam electrons with respect to energy is determined by the method of attenuation of beam current using aluminum filters with different thicknesses. The maximum of such a distribution corresponds to an electron energy of about 100 keV. The maximum exposure dose of X-ray radiation behind a copper-foil anode with a thickness of 30 μm is about 107 mR. It is shown that the beam electrons absorbed by elements of an X-ray detector affect the shape and amplitude of the desired signal at beam currents of greater than 35 A/cm2.