A new analytical formulation is proposed to solve the diffusion equation under Approximation B in electron-photon cascade theory. The Suzuki-Trotter formula, analytical continuation of the hypergeometric function, and product integration are introduced. By using these methods the usual series solutions are obtained, and summation of the infinite series for arbitrary values of the energy E is performed by using the method of Prony's interpolation. As E~ 0, the infinite sum for the electron component turns out to be the function of Kl(8, -8) used in the usual cascade theory, and a logarithmic divergence arises for the photon component. Use of Prony's method makes it possible to derive the energy spectra as well as the track length distributions and the transition curves. Our numerical results agree well with previous authors' as expected. Our analytical approach provides a general framework for solving other diffusion equations containing non-commutative operators in different contexts. at University of North Dakota on May 29, 2015 http://ptp.oxfordjournals.org/ Downloaded from 350 N. Nii agreement with previous results within the limits of the approximation ( § §3 and 4). The incomplete part of our previous formalism has thus been totally completed.Applying the method of Prony's interpolation 11) to our infinite series solution, we can obtain a simple expression of the cascade function, as shown in (1·1), in which the electron energy E is meaningful from 0 to Eo -€t:As a result, it becomes possible to easily obtain with high accuracy the value of the integral energy spectra for any value of energy E ( §5). Our numerical results on the cascade functions, i.e., the electron transition curves, JI(Eo, 0, t) and JI(Wo, 0, t), and the electron track length distributions, Zrr(E o , E) and Zrr(W o , E), are compared P = (-t,' --=:0) (radiation operator), Q = (€(8~8E) ~) (ionization loss operator), and, P and Q do not commute (PQ -QP -=I 0).