(e⁺, He) Total Scattering

Abstract

The total scattering cross section for e+ in He has been measured through two energy intervals, 1 to 4 eV and 17 to 26 eV. Through the lower elastic-scattering interval our results are consistent with the calculations of Drachman. From below the positronium formation threshold, at 17.8 eV to above the He ionization threshold, our results agree qualitatively with the calculations of Kraidy, who includes in his model virtual positronium and positronium polarization. Just below 17.8 eV the cross section is 0.35 ± 0.04 πa02. In these experiments a high-current linac has been used as a source of positrons and total beam attenuation has been used to determine the cross section.

Applicability of modified effective-range theory to positron-atom and positron-molecule scattering

“…Applicability of MERT to low-energy positron scattering was already hypothesized in [2]. However, first measurements of total cross sections for positron scattering at low energies on noble atoms come only from seventies [10,11].The most systematic data for noble atoms, extending down to 0.3 eV were done in WSU Detroit lab, using positrons from a short-lived C 11 radionuclid, with about 0.1 eV energy resolution [11]. Those data indicated clearly a rise of the cross section in the zero energy limit in gases, like He, Ar, H 2 , Kr, Xe, CO 2 , see [11].…”

“…Applicability of MERT to low-energy positron scattering was already hypothesized in [2]. However, first measurements of total cross sections for positron scattering at low energies on noble atoms come only from seventies [10,11].…”

“…However, first measurements of total cross sections for positron scattering at low energies on noble atoms come only from seventies [10,11].…”

The scientific contributions of Karl Frederick Canter (1944–2006)

“…Although Cherry first made slow positrons [17] not long after Madansky and Rasetti's pioneering attempt in 1954 [18], his 1958 PhD thesis was never formally published and gained little attention, despite the fact that the evidence he presented in the thesis for a few slow positrons coming from a Cr covered mica surface irradiated by a 22 Na source is completely convincing. Thus, it was not until the work of McGowan and coworkers in 1969 [19][20][21] that people realized what a neat thing had happened. Then, just as people were beginning to make some real measurements of slow positron scattering cross sections using very weak beams, Karl Canter made the pivotal discovery that set the field on the trajectory towards many fruitful results by providing a slow positron moderator that was easy to make and had a high enough intensity for serious atomic physics and solid state physics experiments.…”

Triply differential ionization of Ar by 500 eV positron and electron impact

“…Advances on the methods for beam production, transport and detection (see for example the review of Surko et al [8]) and the development of techniques such as RIMS, COLTRIMS, as well as multi-coincidence measurements [9,10] are now making it possible to start performing differential studies for positron impact. To date, positron impact experiments have included total scattering cross sections measurements [11] in which information for elastic and inelastic processes are presented, measurements of positronium formation cross sections [12][13][14] and measurements of partial cross sections for inelastic processes [15][16][17][18]. Plus a few groups have been able to acquire singly differential data [19] as well as perform doubly differential electron emission studies [20][21][22].…”