Total cross section measurements for positron and electron scattering on molecular hydrogen between 8 and 400 eV

Abstract

An apparatus for the measurement of positron and electron total cross sections on gases is described. The low-energy positrons are produced by moderating high-energy positrons from beta -decay sources. The authors used a 11 C positron source, produced at a proton accelerator and, alternatively, a 22 Na source, combined with various moderators. For electron measurements the secondary electrons originating from the moderator are used. The beam transport system consists of electrostatic lenses and a weak magnetic lens located in the middle of the gas cell. The discrimination against forward scattering is characterised by a cut-off angle of about 6 degrees . The authors' e + -H 2 and e - -H 2 data are compared with the results of recent measurements of similar accuracy performed at University College, London, and Wayne State University (Detroit), and with other e - -H 2 data. The agreement is satisfactory.