  Precision measurements of the positron component in the cosmic radiation
provide important information about the propagation of cosmic rays and the
nature of particle sources in our Galaxy. The satellite-borne experiment PAMELA
has been used to make a new measurement of the cosmic-ray positron flux and
fraction that extends previously published measurements up to 300 GeV in
kinetic energy. The combined measurements of the cosmic-ray positron energy
spectrum and fraction provide a unique tool to constrain interpretation models.
During the recent solar minimum activity period from July 2006 to December 2009
approximately 24500 positrons were observed. The results cannot be easily
reconciled with purely secondary production and additional sources of either
astrophysical or exotic origin may be required.
