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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.

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