We present a detailed analysis of the energy dissipation averaged over a distance r,epsilon(r), in terms of a stochastic process through scales. Using experimental data recorded in a low temperature helium jet, we give evidence that the probability density function of In (epsilon(r)) obeys a Fokker-Planck equation. The drift and diffusion coefficients are calculated directly from the data. The drift is linear in In(epsilon(r)) and the diffusion is constant. With these coefficients, the equation can be solved exactly, giving a Gaussian probability density function for In(epsilon(r)). The mean and variance of this quantity are discussed in comparison with other log-normal models of intermittency.