Theoretical Research On Distorted Effect And Correlation Effect In He (e,2e) Process

In the (e,2e) reaction of helium, we adopt first-order distorted wave Born approximation theory(DWBA), BBK theory and DS3C theory to investigate distorted effect, correlation effect and dynamics screening effect in coplanar asymmetric geometry. The triple differential cross sections (TDCS) are calculated and the theoretical results were compared with experimental measurements at incident of intermedium and low energy.Theoretically, the first was that the first-order distorted wave Born approximation theory was described. The distorting potential of the incident electron was always chosen to be the spherical average of the initial atomic state. Also, the distorting potential of scattering and ejected electron were chosen to be the spherical average of the final ionic state. Distorted wave which described these electrons was calculated using these distorting potential. Then the triple differential cross sections (TDCS) were calculated using partial wave expansions. TDCS were calculated with the first-order Born approximation theory in which those electrons were described with plan wave and coulomb wave, in order to compare to other theories mentioned above. Thus it was investigated that these effects give an excellent agreement with the measurements of helium.The second was that the BBK theory and the DS3C theory in which contain the effects of the final-state wave state Coulomb interaction between the scattering electron and the ejected electron(PCI) using the Sommerfeld parameters in the (e,2e) reaction of helium.The four bodies problem was reduced to the coulomb three bodies. In the DS3C theory, the effective shield of the residual electron in the final state of he+ is futher modified. Such a modification represents a dynamic screening of the four bodies in the final state. Finally, the scattering amplitude was calculated in detail in first-order distorted wave Born approximation theory.In results and discussion section, the triple differential cross sections for electron-impact ionization of helium (e,2e) reaction are calculated at incident energies of 634.59,604.59,400,250 and 150 eV respectively. The distorted wave Born approximation theory give a relatively good agreement with experimental data particularly for energies of incident electron higher than about 250 eV. It demonstrated that the distorted potential is close to real potential. However, as the energy of incident electron is decreased, DWBA started to fail and one source of this failure may be an inadequate treatment of interaction between the scattering electron and ejected electron.BBK and DS3C has been successful for calculating the TDCS of helium (e,2e) reaction especially in binary peak.The results of BBK and DS3C coincided of the experiments better than the calculation result of DWBA.It demonstrated that DWBA is an inadequate treatment of interaction between the two outgoing electons for the case of lower energies of incident electron. However, as the energy of incident electron is decreased, the degree of agreement with the experiments may have a downward trend. DS3C described the experimental data in a lager ejected electron angle range, but it estimated the angle position in the recoil peak.Electrons were described in BBK and DS3C models. These approaches may not be appropriate since helium ion cannot be reasonably represented as a point charge even if effective charges are used. Further more, the TDCS is depengdent on the choose of the boundary condition, but the boundary condition cannot be determined prioritily.In recoil peak, for the case of incident electron energy of 400 eV ande ejected electron energy of 10 eV, the results of BBK and DS3C can give a relatively good description of experimental data; for other cases,the results of BBK,DS3C and DWBA failed to described the experimental data. The results for the case of higher ejected electron energy were better than result for the lower ejected electron, one source may be that the final state is more responsible for recoil peak and the description of ejected electron in these theories is close to exact asymptotic wave function for the higher ejected electron.The correlation effect and distorted effect can improve the results of theory comparing with the experimental results in the (e,2e) reaction of helium. If DWBA equivalent of the final channel wave function of BBK can be used, this may be an exact asymptotic solution of three-body problem and give a better description of the experimental data.