Kinematically complete experimental study of Compton scattering at helium atoms near the ionization threshold

Compton scattering is one of the fundamental interaction processes of light with matter. Already upon its discovery [1] it was described as a billiard-type collision of a photon kicking a quasi-free electron. With decreasing photon energy, the maximum possible momentum transfer becomes so small that the corresponding energy falls below the binding energy of the electron. Then ionization by Compton scattering becomes an intriguing quantum phenomenon. Here we report a kinematically complete experiment on Compton scattering at helium atoms below that threshold. We determine the momentum correlations of the electron, the recoiling ion, and the scattered photon in a coincidence experiment finding that electrons are not only emitted in the direction of the momentum transfer, but that there is a second peak of ejection to the backward direction. This finding links Compton scattering to processes as ionization by ultrashort optical pulses [2], electron impact ionization [3,4], ion impact ionization [5,6], and neutron scattering [7] where similar momentum patterns occur.Comment: 7 pages, 4 figure

Theoretical study of (e, 2e) process of atomic and molecular targets

Triple differential ionization cross sections (TDCSs) by electron impact are calculated for some atomic and molecular targets by using several models where Post Collisional Interaction (PCI) is taken in account. We also investigate the effect of the short range potential and describe the ejected electron either by a Coulomb wave or by a distorted wave. Significant differences are observed between these models. A better agreement with experimental data is achieved when the short range potential and distortion effects are included

Comptonionization of hydrogen atom near threshold by photons in the energy range of a few keV: nonrelativistic approach

Recently, there have been published the results of unique experiments on measuring the fully differential cross sections of the Compton single ionization of the helium atom near the ionization threshold at a photon energy of a few keV. This opens up a possibility of using Compton ionization along with the ionization of atoms/molecules by fast charged particles to study characteristics of the ionization processes in more detail, since photons are neutral particles. In this regard, the paper deals with the ionization cross sections of the reaction (γ, γe) at the hydrogen atom, because the theoretical description of this reaction at the hydrogen atom does not need to consider a number of additional assumptions and approximations inherent in heavier atoms. Special attention is paid to the study of the kinematic region of the reaction near threshold, where it is expected to obtain a valuable information about the initial and final states of the target. The contribution of corrections to the first Born approximation due to the electron boundness is also discussed

Effect of orthogonalization on total ionization cross sections by electron impact: application to small molecules

Total ionization cross sections by electron impact are calculated for H2O, NH3 and CH4 molecules by using an improved first Born approximation which has been previously applied for atomic targets by Bartlett and Stelbovics [P.L. Bartlett, A.T. Stelbovics, Phys. Rev. A 66, 012707 (2002)]. In this model a full orthogonalization of the final state to the initial state has been performed to evaluate the cross sections. One center wave functions are employed to describe the molecular orbitals. It is shown that the results obtained in the present model are immensely improved when compared with the first Born model without orthogonalization. Furthermore, an overall agreement is also observed when a comparison is made with the experimental data