1. V. A. Ambartsumyan, Zh. Éksp. Teor. Fiz. 13, 323 (1943).
2. R. V. Dashen, Phys. Rev. A 134, 1025 (1964).
3. V. P. Afanas’ev and A. V. Lubenchenko, Poverkhnost, No. 9, 12 (1997).
4. S. Chandrasekar, Radiative Transfer (Oxford Univ. Press, Oxford, 1950; Inostrannaya Literatura, Moscow, 1956).
5. V. S. Remizovich and V. V. Marinyuk, in Proceedings of the 14th International Conference on Ion-Surface Interaction, Moscow, 1999, Vol. 1, p. 384.