  Intensities of hydrogen Balmer-series lines are sensitive to distribution of
populations of sublevels of excited state due to difference of radiative decay
branching ratio for sublevels with different orbital quantum number. Since
these sublevels are degenerate transitions between sublevels and mixing of its
population may be caused by very weak action of environment. A beam of fast
hydrogen atoms is a system in which these fine effects of population mixing can
be observed. Experimental data of H-alpha line radiation intensities in
hydrogen neutral beams are compared with calculations assumed different models
of sublevel population. The comparison most probably point out that population
mixing effects cause transitions from long-lived 3s to 3p sublevel with
corresponding changes in H-alpha radiation intensities. Discussed effects may
influence to results of Doppler-shift spectroscopy measurements of the neutral
beam parameters such as species and impurities content and neutralizing
efficiency.
