The present invention relates to an apparatus for producing a radioisotope by irradiating a target fluid comprising a precursor of said radioisotope with a particle beam produced by a particle accelerator, the apparatus comprising: —a housing comprising a target cavity for receiving said target fluid, said housing having an opening for allowing the passage of the said particle beam into the said cavity; —a dual foil flange for closing said opening of the target cavity, said dual foil flange comprising: —a standoff comprising a central hole; —a first and a second foil able to allow the passage of the said particle beam and located respectively on a first side and a second side of the said standoff, covering the said central hole and forming a cooling cavity; —a first flange and a second flange for sealing respectively the said first and second foil on said standoff; —at least an inlet channel and at least an outlet channel, for flowing a cooling fluid through the cavity of the dual foil flange; —guiding means for positioning said dual foil flange in an in-line position in which a said foil is facing said opening of said housing.