Abstract: Apparatus for the exchange of emission sources of a particle accelerator located in an accelerator vessel filled with a gaseous insulating medium, comprising a gastight source-exchange chamber (3) which is connected by means of a line (26) that can be closed by an exchange valve (8) to the accelerator vessel (17), the said chamber (3) being provided on the inside with a movable exchange member (4 and 5, respectively) having at least one hole (41 and 51, respectively) and at least two holders (43, 44 and 53, 54, respectively) for the emission sources (6a, 6b) to be exchanged, one or more lead-through rods (1) for the transfer of an emission source from the accelerator vessel (17) to the exchange chamber (3) or from the exchange chamber (3) to the accelerator vessel (17), as well as means for placing the movable exchange member (4 and 5, respectively) in the desired position relative to the exchange valve (8).