The scattering of a photon by an electron is called Compton Effect. Energy and momentum are conserved in such an event, and as a result the scattered has less energy (longer wavelength) than incident photon.

Applying conservation of energy and momentum, we get ${\mathrm{\lambda }}^{\mathrm{\prime }}-\mathrm{\lambda }=\frac{\mathrm{h}}{{\mathrm{m}}_{\mathrm{o}}\mathrm{c}}(1-\cos \mathrm{\varphi })$
Where, $\mathrm{\lambda }$ = Wavelength of incident photon ; $\mathrm{\lambda }$’ = Wavelength of scattered photon ; m_o = Rest mass of electron ; h = Planck’s constant ; c = Speed of light ; $\mathrm{\varphi }$ = Scattering angle.
Now, consider scattering of X- ray photon of wavelength 10pm by a target.