  The two-fluid effects on the radial outflow of relativistic electron-positron
plasma are considered. It is shown that for large enough Michel magnetization
parameter (1969) and multiplication parameter, the one-fluid MHD approximation
remains correct in the whole region where |E| < |B|. In the case in which the
longitudinal electric current is smaller than the Goldreich-Julian one, the
acceleration of particles is determined near the light surface where |E| = |B|.
  It is shown that, as in the previously considered cylindrical geometry
(Beskin, Gurevich & Istomin 1983), almost all electromagnetic energy is
transformed into the energy of particles in the narrow boundary layer. The
relative thickness of this layer is shown to be of the order of the inverse of
multiplication parameter.
