shape the conductors may be arranged to the balloon members in different manners suitable is arranging the conductor by means of a deposition technique such as for instance vacuum deposition the conductor will in that case be very flexible and can adapt to the deformations of the balloon member concerned without an interruption in radioactivity occurring in the conductor and without sacrificing flexibility one can also choose for a wire like conductor however which is glued to a balloon member melted onto it or is included in a double wall with the embodiment illustrated in fig4 the balloon device 35 comprises one balloon member 36 with two radioactive conductors 37 38 the conductor 37 has been arranged just in the outer surface of the balloon member 36 and the conductor 38 has been arranged nearer to the inner surface of the balloon member 36 the conductors can also be arranged on one and the same surface preferably the outer one as can be seen in the figure the conductors 37 38 have once again been arranged in coil shapes whereby the coil axes of these coil shapes are in this case positioned at right angles to each other although in the embodiments shown here each time coil shapes with a cylindrical or spherical basic shape have been shown for the sake of clarity the conductor may be arranged on or within the balloon members in any desired pattern the shape employed also depends on the expanded shape which has been chosen for the balloon member in.