The first measurements of total cross sections for positrons (5–49 eV) colliding with a non-room-temperature gas (namely potassium) are reported. Comparisons of these measurements with the corresponding electron measurements using the same apparatus and technique (a beam-transmission method) indicate an overall degree of similarity that has not been observed for any other target atoms or molecules, which could be related to the large polarizability of potassium atoms.

• Received 1 April 1985

DOI:https://doi.org/10.1103/PhysRevLett.55.488