We consider a system of Kondo impurities with an RKKY interaction ¡ between them. Using the exact solution of the impurity and approximating the effect of but then decreases and vanishes at a quantum critical point (QCP). The approach is useful to calculate thermodynamic properties of Kondo systems out of the QCP.In the past three decades, a large amount of experimental and theoretical work was devoted to the understanding of the Kondo lattice. A review of theoretical results in one dimension is given in Ref. [1]. In spite of this effort, the general form of a solution in more dimensions has not been found and phenomenological approaches [2], based on exact solutions for the impurity [3,4] are still been used for the description of Kondo systems. The nature of the ground state in Kondo lattice materials depends on the competition between two energy scales: the single impurity Kondo temperature, and the RKKY interaction , the physics is dominated by the effective exchange interaction between localized spins, and the system orders magnetically. In agreement with these observations, using a mean-field approximation for the one-dimensional system, Doniach obtained a second-order transition from an antiferromagnetic (AF) ground state for low 1 ) to a non-magnetic Kondo singlet for large 1 ). The temperature of magnetic order and the competition between single ion spin compensation and interatomic RKKY interaction has also been calculated in more dimensions using mean-field approximations [6,7]. However, comparison with numerical results in one dimension suggest that the mean-field phase diagram is incorrect [1].We propose that as long as lattice effects discussed later are not too important, the thermodynamic properties of the system can be described by a model which corresponds to a collection of Kondo impurities interacting via an effective exchange interaction in YbS NiT AlU [8]. The data below 150 K have a shape similar to the exact results for a Kondo impurity with total angular momentum 7/2 (corresponding to Yb K. However, the latter should be multiplied by a factor near 1/3 to fit the experiments. This points to a strong AF interaction 1 between the Yb ions. However, the system does not order due to the dominance of the single ion e