The balanced radiator assembly is an efficient means by which the effects of matrix and neighbouring elements can be overcome in radioisotope X-ray fluorescence analysis technique. A special analysis assembly which is used for determinating an element in samples bontaining high concentration of another element with slightly lower atomic number is described. The principle and construction of this assembly and the results of copper content determination in copper concentrates at some mines are given. Samples analyzed with relative error ≤4% account for 98% of total samples.