Argon effective cross sections

Fig. 5.16. Effective cross-sections (oaO)) = a/v for nitrogen in argon at (a) T=300 K, (b) T=100 K SCS calculated (+) and approximated by fitting law (solid line).

Joachain, C.J. and Potvliege, R.M. (1987). Importance of absorption effects on fast positron-argon differential cross sections. Phys. Rev. A 35 4873-4875. 

In the early 1980s, one of the authors of this chapter began to study argon matrix isolation of radical cations235 by applying the radiolytic techniques elaborated by Hamill and Shida. A central factor was the addition of an electron scavenger to the matrix which was expected to increase the yield of radical cations and the selectivity of the method. For practical reasons, X-rays replaced y-rays as a radiolytic source and argon was chosen as a matrix material because of its substantial cross section for interaction with keV photons (which presumably effect resonant core ionization of Ar). Due to the temporal separation of the process of matrix isolation of the neutral molecules and their ionization, it was possible to obtain difference spectra which show exclusively the bands of the radical cations. 

A common result of all the experiments is that most molecules quench the alkali resonance radiation very effectively with total cross sections ranging from 10 A2 to over 200 A2. However, if the molecule BC is replaced by a rare-gas atom, the quenching cross sections become very small at thermal energies. They are probably below 10 2 A2 for quenching by helium, neon, argon, krypton, and xenon.55 The latter result is easily understood in terms of Massey s adiabatic criterion.67 If Ar is a characteristic interaction range, v the impact velocity, and AE the energy difference between initial and final electronic states E(3p) and E(3s), respectively, then we must have a Massey parameter... 

Montgomery and LaBahn (1970). The number in parentheses following 30 eV indicates the power of ten by which the cross sections have been multiplied. Normalization to theory was done at 30° and 120° by Smith et al. (1990) and at 30° and 60° by Floeder et al. (1988). Reprinted from Physical Review Letters 64, Smith et al, Evidence for absorption effects in positron elastic scattering by argon, 1227-1230, copyright 1990 by the American Physical Society. 

Fig. 4.18. Positronium formation cross sections plotted as functions of the positronium kinetic energy for the following gases (a) helium, (b) neon, (c) argon, (d) krypton, (e) xenon. The ionization threshold in each case is indicated by ion . Reprinted from Physical Review A50, Moxom et al, Threshold effects in positron scattering on noble gases, 3129-3133, copyright 1994 by the American Physical Society.

Figure 4.38 Total cross sections for the scattering of electrons on rare gases. This cross section is given by

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