Positron and electron impact double ionization of argon: How 1st- and 2nd-order mechanisms influence the differential electron emission

Abstract

Double-to-single-ionization ratios for electron emission as a function of the angle are measured for 200, 500, and 1000 eV positron and electron impact on argon. Both the sign of the projectile charge and the impact energy are shown to influence the angular dependences. By combining these ratios for positron and electron impact, information about how first-and secondorder double-ionization mechanisms interfere and contribute to the total differential electron emission at different collision velocities is obtained.

Triply differential measurements of single ionization of argon by 1-keV positron and electron impact

“…This work (and our previous studies [9][10][11]) also helps to establish how atomic interactions such as electron exchange, polarization effects, and post-collision interactions contribute, thus allowing for a better understanding of positron interactions, which is an important subject in a variety of fields, e.g. production of antihydrogen and derived fundamental studies of QED, CPT and gravitational forces on antimatter [12], applications such as PET imaging in medicine [13][14][15], as well as characterization of materials by techniques such as ACAR [16][17][18].…”

“…Here we concentrate only on the ejected electron TDCS data. As described in previous publications [9][10][11]20] 2D spectra are generated for scattered projectiles, where one axis corresponds to the projectile scattering angles and the other to the energy loss. Forward scattered projectiles were limited to a horizontal scattering range (φ scat angle) of 0° ± 2.4 o by a slit at the entrance to the energy analyzer and to vertical scattering angles (θ scat ) between ± 7°.…”

Differential studies and projectile charge effects in ionization of molecular nitrogen by positron and electron impact

“…Singly and doubly differential data are now available for double, as well as single ionization [18][19][20][21].…”

“…More importantly, the first triply (fully) differential studies were performed at University College London (UCL) in the 1990's [22][23][24] where scattered and ejected particles leaving in the extreme forward direction were measured in coincidence. These were followed by our work at the Missouri University of Science and Technology (MST) which covered a wider range of emission angles for ionization of argon [10,21,[25][26][27][28][29][30], plus in various conference presentations and papers]. More recently, a collaborative effort between groups in Germany and Australia have reported triply differential data for positron impact ionization of helium [31].…”

Doubly and triply differential ionization measurements using femtoamp beams of positrons and electrons

“…In the past decade, systematic progress in overcoming the bottleneck of low beam intensities and extending experimental differential studies to a wider range of kinematic conditions has been made at the Missouri University of Science and Technology. Our work has culminated in fully kinematics measurements of single ionization [8,16] plus singly differential measurements of double ionization [17]. In both cases, differential data have been obtained using subfemtoamp beam intensities.…”