APROXIMACION POR ESCALONES Appilcation of the green function method to the nuclei Zr 90 and Kr 86 1 BETA RATIO 1 FUNCION DE GREEN 1 FUNCIONES DE ONDA 1 GREEN FUNCTION 1 KRYPTON 86 REACTIONS 1 LADDER APPROXIMATION 1 MODELOS DE CAPAS 1 NTERACCIONES RESIDUALES 1 RESIDUAL INTERACTIONS 1 SHELL MODELS 1 WAVE FUNCTIONS 1 ZIRCONIUM 90 REACTIONS 1