Numerical solutions (solid lines) and the analytical solutions according to Eq. (6) (open circles). The time step Δt= 20 years for numerical solutions in this case. Here, we have assumed that the molecular cloud is passive (i.e., there are no CR sources inside it) and homogeneous (α = 0) with a constant gas density of n_H = 500 cm⁻³ (n₀ = 1000 cm⁻³ due to x⁰ = 1). We have also assumed that the abundance of gas helium is 0.0925 relative to the gas H density, i.e., n_He = 0.0925n_H. The dimension of the cloud R = 20 pc. The spatial diffusion coefficient D₀ = 1.63 × 10²⁶ cm²/s, and the exponent δ = 1/3.