Ramsauer

Here the left-hand side is the ratio of power loss at time t, when the mean electron energy is (E), to that at thermalization, and C and n are determinable constants. This idealized equation is not expected to be valid in presence of the Ramsauer effect, but Warman and deHaas apply it anyway to N2, Ar, and He at atmospheric pressure. The method relates the gradual decrease of collision frequency to an increase in conductivity, which finally rides to a plateau interpreted to be the thermal conductivity. The time needed to reach 90% of the thermal conductivity is called the thermalization time (see Table 8.1). 

Sowada and Warman (1982) have described a dc conductivity method for Ar gas at 295 K and 45 atm. Following a 20-ns pulse of irradiation, the conductivity rises to a peak at -50 ns, due to the Ramsauer effect, before settling to a plateau, which is ascribed to thermal conductivity since the collecting field is very low. Since there is little electron loss, the conductivity profile is proportional to the mobility profile this in turn can be considered a kind of image of collision frequency as a function of electron energy. The time to reach the conductivity plateau, -150 ns, is the measure of thermalization time in the present case. At a density of -9 X 1021 cm-3, the conductivity maximum vanishes, indicating the disappearance of the Ramsauer minimum according to Sowada and Warman. 

G Lewin, G Kuhn, U Deuse, M Buhring, B Ramsauer, I Popov. Paradox of the antiradical capacity of blood plasma proteins. In SFRR Europe Summer Meeting, July 2-5, 1999, Dresden, Germany. Book of Abstracts, p 029. 

Observations on the dimensions of the constituent molecules were made by A. 0. Rankine,8 E. Dorn, W. Sutherland, W. Altberg, C. Ramsauer, and P. Lenard. The mean velocity of the molecules, at 0° and 760 mm. press., is given as 44,690 cm. per second the mean free path, 0-05608 cm. and the molecular diameter, 0-0731 cm. K. S. van Dyke, and E. Blankenstein discussed the coeff. of slip, and of momentum transfer in air and D. Brunt, the kinetic energy of the atmosphere. 

R. Romer, Mem. Acad. Sci. (Paris) 1675 see also C. Ramsauer, Grudversuche der Physik in historischer Darstellung I, Springer-Verlag, 1953. 

The reason for the large difference between the values of A for positrons and electrons at an energy of 2 eV is that for positrons the s-wave phase shift passes through zero at the Ramsauer minimum and the dominant contribution to the cross section therefore comes from the p-wave, which is quite strongly peaked in the forward and backward directions. In contrast, there is no Ramsauer minimum in electron-helium scattering, and the isotropic s-wave contribution to aT is dominant at this energy. 

Kauppila, W.E., Stein, T.S. and Jesion, G. (1976). Direct observation of a Ramsauer-Townsend effect in positron-argon collisions. Phys. Rev. Lett. 36 580-584. 

To be sure, the experiments of Nicholson and Merton on the radii of the atomic orbits in mixtures of hydrogen and helium relative to the distance between molecules and of Ramsauer on the long free paths of electrons in argon and other gases do not favor Coulomb s law. It may be that the repulsion between nuclei and the attraction between nucleus and electron follow different laws. 

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

This equation becomes important if, for example, one considers scattering of 1 eV electrons on xenon in a deflection analyser with 0 = 45°. From Fig. 4.38 one would conclude that scattering effects are small because the scattering cross section is small (Ramsauer minimum), but the reduction of kinetic energies towards the turning point increases [Pg.147]

Fig. 2. Scattering cross sections for pt with a hydrogen isotope nuclei from Refs. [12,18], showing the Ramsauer-Townsend minimum at around 10 eV for pt+p pt(F) +t cross sections plotted include both elastic and spin exchange reactions, where pt(0) is the singlet state and pt( 1) is the triplet state...

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