[en] Melt is prepared from MoO₃ powder containing ⁹⁹Mo and an oxide or molybdate of another metal, eg., Cu. The melt containing ⁹⁹Mo can also be prepared by mixing non-active MoO₃ with an oxide or molybdate of another metal and by irradiation in a reactor following melting and cooling. The melt is bubbled with a carrier gas or, alternatively, the carrier gas is passed above the melt and entrains the sup(99m)Tc released which condensates in a condensation vessel. The advantage of the method is separation efficiency exceeding 80%. (J.P.)