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Published online by Cambridge University Press: 26 May 2016
The problem of non-LTE populations has been considered in terms of the departure coefficients ∂bn/∂n as functions of the kinetic temperature Te, the electron density Ne, the continuum radiation flow Ic and the ratios of IHnα, IHnβ, IHnδ and IHnε (the line radiation flows). The ratio of IHnα/IHnβ are sensitive to the thermal radiation from HII regions. Characterized by the relation of ∂2bn/∂n2 > 0, the populations are shown to be inhabited radiatively.