  The well-known treatment of asymptotically flat vacuum fields is adapted to
pure radiation fields. In this approach we find a natural normalization of the
radiation null vector. The energy balance at null infinity shows that the mass
loss results from a linear superposition of the pure and the gravitational
radiation parts. By transformation to Bondi-Sachs coordinates the Kinnersley
photon rocket is found to be the only axisymmetric Robinson-Trautman pure
radiation solution without gravitational radiation.
