Abstract: An apparatus and method for positron fueled ramjet operation is provided including a convection chamber for a ramjet comprising a rate of absorption of gamma rays that yields a uniform heating of the convection chamber to a temperature sufficient to sustain ramjet operation. The convection chamber may comprise at least one open ended cylinder, a plurality of concentrically arranged cylinders, a plurality of rods, a honeycomb structure or other structures for absorbing gamma rays. A ramjet powered by gamma rays is also provided that includes a housing forming a fluid passageway. A reaction vessel is positioned within the housing, and arranged in flow communication with a source of positrons. A gamma ray absorption assembly is positioned within the fluid passageway so that as positrons interact with electrons and annihilate, gamma rays impinge upon the gamma ray absorption assembly.