Absolute differential and total cross sections for the scattering of positrons from helium

Abstract

We have measured absolute differential and total cross sections for positrons scattered elastically from helium at energies from 44.9 to 84.7 eV. The results are compared with theory, and, in addition, the total elastic cross sections are compared with values obtained by subtracting total inelastic cross sections from total cross sections for scattering into all channels. Agreement between the two sets of experimental total elastic cross sections is quite good. Agreement with theory is fair at the lower energies, but the theoretical values decrease with increasing energy while the experimental results are essentially constant at the higher energies. The experimental and theoretical differential cross sections both exhibit secondary maxima, but the experimental values are much larger. The theoretical values extend from 0 to 180°, but we have detected no elastically scattered positrons at angles in excess of 48°.