Observation of Bhabha scattering in the center-of-mass kinetic-energy range 342 to 845 keV

Positrons from a Si27 source, obtained through the reaction Al27(p,n) 27Si, were scattered off electrons in a target of polyethylene, and e+e- coincidences were detected in a pair of plastic scintillators. The detector aperatures were restricted to accept only events corresponding to maximum momentum transfer at center-of-mass angle /2. The variation with energy of the corresponding laboratory angle was utilized to obtain the scattering excitation function from the continuous positron spectrum. Center-of-mass kinetic energies in the e+e- system covered the range 342 to 845 keV.