We discuss recent observations of high energy cosmic ray positrons and electrons in the context of hadronic interactions in supernova remnants, the suspected accelerators of galactic cosmic rays. Diffusive shock acceleration can harden the energy spectrum of secondary positrons relative to that of the primary protons (and electrons) and thus explain the rise in the positron fraction observed by PAMELA above 10 GeV. We normalize the hadronic interaction rate by holding pion decay to be respons...Expand abstract
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13 pages, 8 figures (ReVTeX 4); Clarifying comments added; Revised
prediction for B/C added (new Fig.8); References added; To appear in Phys.