18. A narrow beam of monochromatic x-ray radiation is incident on the scattering substance. In this case, the wavelengths of radiation scattered at angles θ1 = 60 ° and θ2 = 120 ° differ from each other by η = 2.0 times. Assuming that scattering occurs on free electrons, find the wavelength of the incident radiation.
 

Detailed solution. Decorated in Microsoft Word 2003. (Target decided to use formula editor)