A mathematical model describing radial diffusion, with violation of the third adiabatic invariant and with local losses, is applied to the Pioneer 10 and 11 observations of omnidirectional integral intensities of electrons with energy E>21 MeV. Local losses outside L=3 are much stronger than synchrotron losses but weaker than the losses one would expect for strong pitch angle diffusion. If radial diffusion is driven by ionospheric winds, as was suggested by Brice and McDonough (1973), we find that the theoretical solution which best fits the data requires that the radial diffusion coefficient D?3¿10-9L3s-1 and the lifetime against local losses, &tgr;, is approximately a few million seconds.