21cm spontaneous rate

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 Joined: September 23 2004
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21cm spontaneous rate
I've seen numbers quoted for A_{10}  the 21cm Einstein A coefficient as 2.85e15/s and 2.869e15/s, but seldom with references. The former number seems to come from Wild 1952, anyone know where the second number comes from? (presumably updated since 1952)
21cm spontaneous rate
I found a reference using the latter number, citing
Field, G. B., "Excitation of the Hydrogen 21cm Line," Proc. IRE, 46, 240250 (1958).
(found a link here)
Field, G. B., "Excitation of the Hydrogen 21cm Line," Proc. IRE, 46, 240250 (1958).
(found a link here)

 Posts: 1512
 Joined: September 23 2004
 Affiliation: University of Sussex
 Contact:
Re: 21cm spontaneous rate
Thanks, but actually that paper cites Wild quoting 2.85e−15/s.
However the 2.869e15/s number seems to follow from just substituting modern values into Wild's result:
[tex]
A_{10} =\frac{2 \pi \nu_{21}^3 \alpha h^2}{c^4 m_e^2 g_2}
[/tex]
(where g_2=3). I wonder if anyone has ever checked Wild's result? (bizarrely based on a personal communication result from someone else!)
However the 2.869e15/s number seems to follow from just substituting modern values into Wild's result:
[tex]
A_{10} =\frac{2 \pi \nu_{21}^3 \alpha h^2}{c^4 m_e^2 g_2}
[/tex]
(where g_2=3). I wonder if anyone has ever checked Wild's result? (bizarrely based on a personal communication result from someone else!)