X-ray equipment Constant potential 2-30 MV Fig 3.2 (6)
Published: Sep 29, 2021

If you take the y-axis value and multiply by 600, this will give you a figure of mGy/ mA h at 1m. Note how exposure rate is significantly affected by filtration.
1 esu = 3.3 x 10-10 coulombs = 2 x 109 ion pairs/cm3 of air. Equivalent to 2.58 x 10-4C/kg air (0.0087 J/kg of air). 1R is approximately 10 mGy (good enough for radiation protection purposes).