An incident X-ray is emitted in a wide angular sector toward an amorphous material specimen which backscatters the X-rays. The method comprises: a step of recording experimental photon intensity measurements as a function of the angle of incidence; a step of correcting the experimental intensity, taking into account at least the absorption phenomena inside the specimen dependent on the penetration length l of the incident wave inside the specimen before reflection; a normalization step referring the corrected intensity arising from the experimental intensity to an electron intensity according to a normalization coefficient (α); a step of calculating a discretized function Q.i(Q), i being a reduced intensity arising from the measurements of the corrected and normalized experimental intensity and Q being the modulus of the wave scattering vector proportional to the quantity (sin θ)/λ, 2θ being the scattering angle and λ being the length of the wave emitted, the normalization constant (α) varying in a recursive manner so as to minimize the slope of the affine straight line obtained by linear regression over the values of the function Q.i(Q), during each iteration the values of the reduced intensity being calculated for a penetration length l, the function Q.i(Q) sought corresponding to the minimum slope; a step of determining the structure factor on the basis of the distribution of the radial atomic concentration ρ(r) dependent on Q.i(Q).