Elastic scattering of two photons by a multicharged atomic ion

The elastic scattering of two X-ray photons by a multicharged atomic ion has been studied theoretically. A pronounced resonance structure and strong angular anisotropy of differential scattering cross section have been predicted in the energy range of a scattered photon from $\hbar\omega- I_{1s}$ to $\hbar\omega+ I_{1s}$ (where $\hbar\omega$ is the energy of the incident photon and $I_{1s}$ is the ionization energy threshold of the $1s$-shell of the ion). The absolute value of the observed cross section has been quantitatively estimated.