[en] The ^99mTc are the radionuclide more used in the nuclear medicine, it is used for diagnostic and therapy, and he is commonly takes place by means of a generator ⁹⁹ Mo-^99mTc, using molybdenum (⁹⁹Mo) product of the fission of the uranium, adsorbed over alumina. This generator imposes the use of high activities you specify of ⁹⁹ Mo, as well as of complex processes of separation of the one ⁹⁹ Mo, generating important quantities of radioactive waste of medium activity. As well as, the production of these generators, demands the use of reactors of great capacity that Mexico not it possesses, in such a way that, presently work is carried out a generator of ⁹⁹ Mo- ^99m Tc, in the one which ⁹⁹ Mo taken place by the reaction ⁹⁸ Mo(n, γ) ⁹⁹ Mo that it was part from a gel to base is used of molybdate and zirconium. It was found, therefore, to produce a generator ⁹⁹ Mo- ^99mTc with the help of gels of zirconium and molybdates with the same characteristics of quality and purity that those obtained by the one traditional generator and that it can be carried out under the conditions technical-economics prevailing in Mexico. Specifically, this work has been focused to the study of the effect caused by the variation of the one p H in the solutions of ZrOCl₂ * 8H₂O (zirconil) and of molybdates, of the relationships molars zirconium : molybdenum (Zr:Mo), as well as the effect of the concentration variation, time of preparation and consequently p H of the ZrOCl₂ * 8H₂O in the synthesis of the gel zirconium - ⁹⁹ molybdenum, on the efficiency of the generator and the quantity of ⁹⁹ Mo presents in the ^99m Tc taken place by this means. The gel used for the production of ^99mTc will possess a discharge efficiency of recovery of ^99mTc and a contained first floor of pollutants, in particular smaller to 0.015% of ⁹⁹ Mo, main source of impurity radionuclide of these generators. The obtained results show that to p H average (3.8 and 4.5), the obtained efficiencies they are the biggest (- 80%). To high concentrations of the zirconil used in the synthesis of those gels (0.5 M), the efficiencies are low and with contained first floor of ⁹⁹ Mo in the eluates; while that, to low concentrations of ZrOCl₂ * 8H₂0 (0.045M), the efficiencies increase, but also the quantity of ⁹⁹ Mo present in the eluates. At the using solutions of ZrOCl₂ * 8H₂O prepared one day before the synthesis of the gel, bigger efficiency is obtained. The suitable p H of this solution this in the interval of 0.7 at 1.5. The relation Zr:Mo but convenient for to synthesize the gel is 1:1, because to this relation Zr:Mo the efficiency of the generator is bigger than the 80 %. Therefore, the choice of each one of the parameters studied in this work, it should be then a commitment among: high efficiency of the generator ⁹⁹ Mo- ^99mTc and contained first floor of ⁹⁹ Mo in the eluates. (Author)