Speaker
Description
Recently unique experiments have been carried out to measure the fully (FDCS) and single (SDCS) differential cross sections of Compton ionization of helium atoms near the threshold of single ionization [1]. The photon energy was about 2 keV, and the energy of the detected electrons did not exceed 10 eV.
An adequate theoretical description in this energy range can be carried out in the framework of the so-called $A^2$ approximations. The corresponding matrix element looks exactly like the usual first Born approximation (FBA) in the case of ionization of an atom by a fast particle (electron, proton, heavy ion). This analogy allows us to treat the process under consideration on a par with such well-known methods of spectroscopy of the outer shells of atoms and molecules as (e, 2e), (p, pe), etc. It should be noted that the contribution to the second-order matrix element of the term including two sequential dipole transitions is extremely small in this kinematic region, which makes Compton ionization a valuable spectroscopic tool.
