Abstract: A gas target device in which a gaseous target is bombarded with charged particles by means of a charged particle accelerator and radioisotopes are produced in a target chamber receiving the gaseous target a vacuum chamber is disposed in front of the gas target device so as to provide safety volume with gas-tight metal foils disposed at both ends thereof which metal foils however are permeable to the charged particles but provide a gas-tight seal with respect to the target chamber of the gas target device and the vacuum system of the accelerator. The metal foils are held by flanges disposed between the housing which are movable relative to one another to permit removal and replacement of the metal foils associated with the flange plates.