present from the material and for relaxation of the entire hollow body the monocrystalline hollow bodies 8 produced in this way have outstanding electrical properties wherein circulating currents are present in the monocrystalline surface layer of the superconductor niobium and prevent an external magnetic field from penetrating internally whereby superconductivity is not disturbed moreover by means of the monocrystalline material significantly reduced roughnesses in particular of the internal surface can be achieved which are 25 nm in the case of a concluding bcp treatment fig6 shows a multiplicity of hollow bodies 8 8 u2032 8 u2033 which have been produced in accordance with the method described above and joined together analogously to the joining of two half cells 5 and 5 u2032 to form a hollow body 8 at their termination areas 7 u2032 7 u2033 7 u2033 u2032 7 u2033 u2033 preferably likewise by electron beam welding this means that the markings 3 3 u2032 3 u2033 3 u2033 u2032 3 u2033 u2033 3 u2032 u2033 u2033 adjacent to the termination areas 7 7 u2032 7 u2033 7 u2032 u2033 7 u2033 u2033 7 u2032 u2033 u2033 are arranged with respect to one another as on both sides of the cut areas 2 and 2 u2032 between the wafers 4 4 u2032 from which the corresponding.