As is known, the semiclassical approximation applies to the solution of the Schrödinger equation - ℏ/2m d² ψ (χ)/dχ² + U (χ)ψ(χ) = Eψ(χ) (5.1) if the potential U(χ) changes slowly at the distances on the order of the de Broglie wavelength of the particle, i.e., at those distances where the solution ψ (χ) itself varies essentially. Equation (5.1) can be rewritten somewhat otherwise: d²ψ(χ)/dχ² + κ² (chi;)ψ(χ) = 0, κ²(χ = 2m/ ℏ² [E - U(χ)]. (5.2) Now the condition of applicability of the semiclassical approximation is that κ(χ) should vary slowly at the distances on the order of 1/κ(χ). Equation (5.2) describes in fact a sufficiently wide class of phenomena, in no way confined to quantum mechanics. One such problem will be considered below.