[en] The generator system of radionuclides more diffused, and used in the world, it is the⁹⁹Mo / ^99m Tc. These use ⁹⁹ Mo, product of fission of the ²³⁵ U of very high specific activity, adsorbed on alumina (0.2% of ⁹⁹ Mo/gram of alumina). An alternative for the production of generators of low activity specifies, via the reaction ⁹⁸ Mo(n, γ) ⁹⁹ Mo, it is based on the use of compounds with molybdates base, as matrices of the generators ⁹⁹ Mo / ^99m Tc. In this work is proposed to develop a generator at base of compounds of magnesium molybdates that could be irradiated after its synthesis, given the short half life of the only radioisotope produced by magnesium: ²⁷ Mg (t_1/2 = 9.46 m). In this work two parameters were studied, fundamental in the preparation of the magnesium molybdates, matrices of the generators ⁹⁹Mo / ^99mTc, and their influence in the efficiency and radionuclide purity: the washing of the gels previous to its irradiation and the molar ratio Mo:Mg. The magnesium molybdates non washing presents bigger efficiencies (72%), but they don't fulfill a smaller percentage to 0.015% of ⁹⁹ Mo, neither with a radiochemical purity of 90%, except when the molar ratio Mo: Mg of 1:1.08 which provide the best results. (Author)