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We show that the positron excess measured by the PAMELA experiment in theregion between 10 and 100 GeV may well be a natural consequence of the standardscenario for the origin of Galactic cosmic rays. The 'excess' arises because ofpositrons created as secondary products of hadronic interactions inside thesources, but the crucial physical ingredient which leads to a naturalexplanation of the positron flux is the fact that the secondary productiontakes place in the same region where cosmic rays are being accelerated.Therefore secondary positrons (and electrons) participate in the accelerationprocess and turn out to have a very flat spectrum, which is responsible, afterpropagation in the Galaxy, for the observed positron 'excess'. This effectcannot be avoided though its strength depends on the values of theenvironmental parameters during the late stages of evolution of supernovaremnants.

The origin of the positron excess in cosmic rays