214 .REFERENCES 1, Vogt, E. and Wannier, G. H. Phys. Rev. 95, 1190 (1954). 2. Dalgarno, A. Adv. in Phys. 11, 281 (1962). 3. Pauling L. The Nature of Chemical Bond, Cornell Univ., Press, 1960, 3rd. ed., Ch. 13; also Hirschfelder, J. O., Curtiss, C, F., and Bird, R. B. Wolecudar Theory of Gases and Liquids. Wiley, New York, 1964. 4, O'Malley, T. F., Spruch, L., and Rosenberg, L. J. Math. Phys. 2, 491 (1961). 5. Newton, R. Scattering Theory of Particles and Waves. McGraw-Hill, New York, 1966. 6. Weber, G. G. and Bernstein, R. B. J. Chem. Phys. 42, 2166 (1965). 7. Waech, T. G. and Bernstein, R. B. J. Chem. Phys. 46, 4905 (1967). 8. Fermi, E. Nuove cimentoe 11, 157 (1934); for further references, see Breene, R. G., Jr. The Shift and Shape of Spectraf Lines. Pergamon Press, New York, 1961, Ch. 7. GENERALIZED OSCILLATOR STRENGTHS OF THE HELIUM ATOM. Hit. TRANSITIONS FROM THE GROUND STATE TO THE 3'D AND 4'P STATES* Y.-K. Kim and Mitio Inokutz The generalized oscillator strengths of He for the LS — 3D and 4!P transitions have been calculated with correlated wave functions, according to both the length and velocity formulas. The agreement between * Abstract of an article published in Phys. Rev. 184, 38-43 (August 5, 1969). the two alternative results is within 3%or less for moderate values of the momentum transfer. The resulting Born cross sections for charged-particle impact ure also given. Compared with our values, available experimental data on the 3\D excitation are substantially larger, while for the 4'P excitation they agree within +50 %. SPECIFIC PRIMARY IONIZATION FF. Rieke and William Prepejchal Primary ionization cross sections have been measured for 16 additional gases. Present and previous results are summarized in graphical form, New measurements show that high-energy positrons and electrons have primaryionization cross sections that are equal within one percent. Primaryionization cross sections have been measured for 16 newgases, supplementing work reported earlier™. The results are given in the first 16 lines of Table 77. Early in the investigation, measurements were made on several gases with positrons as primaries; these measurements were in the nature of absolute determinations. The results indicated that the cross sections for positrons might be shghtly greater than for electrons, but the excess was well within the uncertainty of the absolute determinations. We have recently made somerelative measurements that afford a much more accurate comparison. For these measurements, a source was prepared to contain suitable activities of both Co** for positrons and Ce!4-Pr™4 for electrons. With such a mixed source, it was possible by simply reversing the current in the magnetic analyzer to measure counter efficiencies for positrons and for electrons alternately while maintain- ing exactly constant counting conditions. To avoid uncertainties in analyzer calibration with field reversed, the field strength was monitored throughout with a gaussmeter. Comparisons were made with argon at primaryenergies where the positrons and electrons gave comparable counting rates. The results are given in Table 78; they indicate that at high energies the ionization cross sections for positrons and for electrons differ byless than a percent. It seems unprofitable to carry the comparison further. In line with our aim of determining cross sections as accurately as is feasible, we have reviewed our older results and made adjustments where they appeared to be indicated. The procedure for obtaining the constants 17? and C from the observed counter efficiencies by the method of least squares has been simplified in that wall effects are represented by one adjustable constant instead of two. The solution now used amounts to assuming that the observed efficiencies 7 can be expressed bytherelation —In (1 — 94) = NEo({E)(P — Po), where Py) represents wall effects and is independent of primary energy /; o(#) follows the Bethe formula. A small systematic error has been eliminated by taking into account scattering of the primary electrons by the