Bulletin of the American Physical Society
75th Annual Gaseous Electronics Conference
Volume 67, Number 9
Monday–Friday, October 3–7, 2022;
Sendai International Center, Sendai, Japan
The session times in this program are intended for Japan Standard Time zone in Tokyo, Japan (GMT+9)
Session GW5: Heavy-Particle Collisions |
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Chair: Masamitsu Hoshino, Sophia University, Japan Room: Sendai International Center Shirakashi 2 |
Wednesday, October 5, 2022 2:30PM - 2:45PM |
GW5.00001: Doubly differential ionization cross sections of proton-helium collisions Kate Spicer, Corey Plowman, Shukhrat Alladustov, Ilkhom Abdurakhmanov, Igor Bray, Alisher Kadyrov We present an investigation of the four-body proton-helium differential scattering problem using the two-center wave-packet convergent close-coupling (WP-CCC) approach. The approach uses correlated two-electron wave functions for the helium target. Here, we focus on doubly differential cross sections for ionization in the intermediate energy (50-300 keV) region where coupling between various channels is important. The greatest difficulty in calculating these cross sections is in representing the final electronic state as the ejected electron travels in the long-range Coulombic fields of both the projectile and the residual target. This state is challenging to take into account. Therefore, available theoretical approaches rely on low-order approximations. Furthermore, there are no comprehensive investigations of all three types of doubly differential cross sections. Our aim is to provide a complete doubly differential picture of ionization and, thereby, fill this gap. We report results for the cross sections differential in any two variables out of three: the projectile scattering angle, the electron ejection angle and energy. Preliminary calculations suggest that the WP-CCC method agrees well with experimental data for all three types of the doubly differential cross sections. |
Wednesday, October 5, 2022 2:45PM - 3:15PM |
GW5.00002: Transcending the impact parameter approach by means of a full quantum distorted wave description of ion-atom and ion-molecule collisions Invited Speaker: Raul Oscar Barrachina The so-called impact parameter approximation is as old as the atomic collisions theory itself. For example, it had already been employed as early as 1930, by "Coen" Brinkman and "Hans" Kramers, in their calculation of the electron capture cross section in the collision of alpha particles with atoms [1]. Perhaps, the best-known justification for its applicability was given by Gian Carlo Wick in a note added in proof by J. David Jackson and H. Schiff [2]. There it is said that "in an exact calculation of the capture process the (nucleus) - (incident particle) interaction will give a negligible contribution (of order of m/M). This can be seen most easily by considering the nuclei to be infinitely heavy and setting the problem up as an impact parameter calculation". This approximation of considering that the projectile-nucleus system follows a classical rectilinear and uniform trajectory was and continues to be widely used in a variety of theoretical models to describe heavy particle impact collisions. Obviously, this approximation fails at large angles [3], but it is expected to be valid if the deflection of the projectile is small (as proposed by Wick, of order of m/M). In this communication we will explore the validity of this assumption, both from a comparative point of view of this semiclassical theory with its fully quantum version, and in the light of the most recent experimental results (see e.g. [4]). |
Wednesday, October 5, 2022 3:15PM - 3:45PM |
GW5.00003: Ion-induced differential ionisation of helium at intermediate energies Invited Speaker: Alisher Kadyrov Theoretical description of electron emission in ion collisions with multielectron targets remains a challenging problem. Even for the simplest case of bare ion scattering on helium, there are no nonperturbative approaches that can provide reliable information about all interconnected reaction channels, in particular, the kinematically complete differential picture of ionisation when electron capture to the continuum (ECC) is important. We have developed a wave-packet convergent close-coupling approach that is capable of providing benchmark data on the integrated and differential cross sections for all processes taking place in such collisions. The approach allows to calculate integrated, fully differential, as well as various doubly and singly differential cross sections for ionisation of atomic targets. The approach has recently been applied to p-He collisions. Calculations of ionisation cross sections differential in the electron emission energy, in the emission angle, as well as in the scattered-projectile angle have been performed in the intermediate energy region. The results agree well with experimental data where available. Moreover, our calculations reveal an interesting interplay between direct ionisation and ECC. The ionisation cross section differential in the angle of the ejected electron is dominated by ECC for ejection into small angles, while ejection into large angles is purely due to direct ionisation. The energy-differential cross section shows that low-energy electrons are emitted due to direct ionisation, while ECC leads to high-energy electrons. When ECC peaks, we see a shoulder in the cross section predicted by experiment. As to the singly differential cross section as a function of the scattered-projectile angle is concerned, at low projectile energies, direct ionisation and ECC have similar behaviour and comparable contributions. However, as the energy increases, direct ionisation becomes dominant. |
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