Abstract: The present invention provides systems and methods for the “in-target” reactions of radioisotopes with various reactants in order to form desired reaction products in useful states. One embodiment of the invention provides a target-holding assembly for use with a gas target and a particle accelerator configured to provide a high-energy beam along a beam axis. The target-holding assembly has a mounting portion attachable with the particle accelerator in alignment with the beam axis. A gas target holder is connected to the mounting portion and has a thermally conductive holder body with a target cavity therein configured to be in axial alignment with the beam axis. The target cavity is shaped and sized to fully contain the gas target therein for bombardment by the high-energy beam. The target body has an inlet port in fluid connection with the target cavity.