Cross sections of discrete-level excitation of noble-gas atoms in Compton scattering

The differential cross section in angle and the total cross sections for the excitation of atomic discrete levels in Compton scattering are investigated. Results are presented for the valent np-n,(n+1)d and np-(n+1),(n+2)p levels of the outer subshells of the noble-gas atoms Ne, Ar, Kr, and Xe, covering the range of the momentum transferred to the atom up to 8 a.u., which is sufficiently large for the calculation of the total Compton excitation cross sections. Calculations were performed in one-electron Hartree-Fock approximation and with many-electron effects taken into account in the random-phase approximation with exchange for monopole, dipole, quadrupole, and octupole transitions. Contributions from higher multipoles proved to be unimportant and many-electron effects were found to be quite noticeable in the differential cross section, while almost negligible in the total excitation cross sections. We conclude that the contributions of discrete excitations are comparable to those of the ionization process.