The cosmic ray positron spectrum

A calculation is made of the flux of secondary positrons expected above 100 MeV for various disk-halo diffusion models, which are consistent with the observed grammage and Be-10 abundance. It is found that models which give a high surviving fraction of Be-10 (about 0.3) give a secondary positron spectrum which is consistent with the observations, while a model predicting a low Be-10 abundance (about 0.1 surviving) gives a poorer fit at high energies hinting at the presence of a primary positron component. Implications of these results are discussed.