Penetrating Electromagnetic Radiation emitted when the inner orbital Electrons of an atom are excited and release radiant energy. X-ray wavelengths range from 1 pm to 10 nm. Hard X-rays are the higher energy, shorter wavelength X-rays. Soft x-rays or Grenz rays are less energetic and longer in wavelength. The short wavelength end of the X-ray spectrum overlaps the Gamma Rays wavelength range. The distinction between Gamma Rays and X-rays is based on their Radiation source.