Abstract
The ratio of the populations in the upper, N U and lower, N 1 levels of the ground state of HI is given by the Boltzmann relation, where the statistical weights in these levels are 3 and 1, respectively: N U/N 1 = 3 exp(−0.0682/T S). We can assume that the spin temperature, T S, equals the kinetic temperature, T K. Calculate the population ratio for a temperature of 100 K. Repeat for a temperature of 3 K (the lowest temperature possible under local thermodynamic equilibrium), for 104 K (the warm interstellar medium) and 106 K. Compare the differences in populations.
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© 2000 Springer-Verlag Berlin Heidelberg
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Wilson, T.L., Hüttemeister, S. (2000). Line Radiation of Neutral Hydrogen. In: Tools of Radio Astronomy. Astronomy and Astrophysics Library. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-57001-8_12
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DOI: https://doi.org/10.1007/978-3-642-57001-8_12
Publisher Name: Springer, Berlin, Heidelberg
Print ISBN: 978-3-540-66802-2
Online ISBN: 978-3-642-57001-8
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