The excess in the positron fraction reported by the PAMELA collaboration has
been interpreted as due to annihilation or decay of dark matter in the Galaxy.
More prosaically, it has been ascribed to direct production of positrons by
nearby pulsars, or due to pion production during stochastic acceleration of
hadronic cosmic rays in nearby sources. We point out that measurements of
secondary nuclei produced by cosmic ray spallation can discriminate between
these possibilities. New data on the titanium-to-iron ratio from the ATIC-2
experiment support the hadronic source model above and enable a prediction to
be made for the boron-to-carbon ratio at energies above 100 GeV. Presently, all
cosmic ray data are consistent with the positron excess being astrophysical in
origin.Comment: 4 pages, 2 figures (RevTex4); revised to include additional data in
figures and references; accepted for publication in PR