Total cross section hydrogen

The final apparatus we describe briefly here is that used by the Detroit group (Zhou et al., 1994a) for the first measurements of the total cross section for positron scattering by atomic hydrogen, and again it... 

The total cross sections measured by Zhou et al. (1997) for positron and electron impact are illustrated in Figure 2.18. As noted by these authors, the positron total cross sections are in excess of those for electrons in the energy range 15-100 eV, a situation similar to that found for the alkali atoms, as described in subsection 2.5.3. The experimental electron-hydrogen data agree well with the semi-empirical values derived... 

Fig. 7.14. The spin-averaged total cross section, and its various components, for positronium-hydrogen scattering, as calculated using a 22-term (21 Ps, 1 H)...

Diana, L.M., Brooks, D.L., Coleman, P.G., Pendleton, P.K., Norman, D.M., Seay, B.E. and Sharma, S.C. (1986a). Total cross sections for positronium formation in molecular hydrogen, krypton and xenon. In Positron (Electron)-Gas Scattering, eds. W.E. Kauppila, T.S. Stein and J.M. Wadehra (World Scientific) pp. 293-295. 

Ferch, J., Raith, W. and Schroder, K. (1980). Total cross section measurements for electron scattering from molecular hydrogen at very low energies. J. Phys. B At. Mol. Phys. 13 1481-1490. 

Zhou, S., Kauppila, W.E., Kwan, C.K. and Stein, T.S. (1994a). Measurements of total cross sections for positrons and electrons colliding with atomic hydrogen. Phys. Rev. Lett. 72 1443-1446. 

Fig. 11. Total cross section for the interaction of relativistic positronium atoms with carbon as a function of the kinetic energy expressed in the rest masses of the incident atom (T = 7—1). The solid curve is the theoretical dependence, - the measured value. The arrow marks the region (7 < 1.2) investigated in experiments on the interaction of hydrogen atoms with carbon...

The difficulties associated with making an atomic-hydrogen target have precluded direct measurements of total cross sections for hydrogen. Estimates may be made by adding the best available estimates for the integrated cross sections of particular channels and the total ionisation cross section. 

To estimate the total cross section for hydrogen we use the n=l and 2 estimates above. For n=3 we interpolate in the direct measurements of integrated cross sections by Mahan, Gallagher and Smith (1976). For higher discrete channels we use the roughly-valid rule that integrated cross sections for principal quantum number n are proportional to n. Very accurate measurements of the total ionisation cross section have been made by Shah et al. (1987). These total cross section estimates are shown in table 8.3 in comparison with the three calculations we are considering. 

Table 8.3. Total cross sections (tioq) for hydrogen. The column headings are as in table 8.2...

In Fig. 8, we show the total cross section for electron capture and electron loss for protons and neutral hydrogen projectiles colliding with atomic and molecular hydrogen, as a function of the projectile energy. The experimental data are from several authors [31-36] and also for comparison we present the theoretical results of Kimura et al. [28]. 

In Fig. 9 we present the results for the total cross section for electron excitations in the 2s and 2p states of atomic hydrogen when proton projectiles collide with energies from l(X)eV up to 300 keV. In the same figure we compare with some available experimental results [37, 39-41]. 

Fig. 9. Total cross section for the excitation of the 2s and 2p hydrogen target states for proton projectiles from 100 eV up to 300 keV. The experimental data are from X, Higgins et al. [37] +, Barnett [38] X, Morgan et al. [39] , Detleffsen et al.

In Figure 2, we show the total differential cross-section for product molecules in the vibrational ground state (no charge bansfer) of the hydrogen molecule in collision with 30-eV protons in the laboratory frame. The experimental results that are in aibitrary units have been normalized to the END... 

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