21cm spontaneous rate

Post Reply
Antony Lewis
Posts: 1512
Joined: September 23 2004
Affiliation: University of Sussex
Contact:

21cm spontaneous rate

Post by Antony Lewis » February 05 2007

I've seen numbers quoted for A_{10} - the 21cm Einstein A coefficient as 2.85e-15/s and 2.869e-15/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)

Ben Gold
Posts: 81
Joined: September 25 2004
Affiliation: University of Minnesota
Contact:

21cm spontaneous rate

Post by Ben Gold » February 06 2007

I found a reference using the latter number, citing

Field, G. B., "Excitation of the Hydrogen 21-cm Line," Proc. IRE, 46, 240-250 (1958).

(found a link here)

Antony Lewis
Posts: 1512
Joined: September 23 2004
Affiliation: University of Sussex
Contact:

Re: 21cm spontaneous rate

Post by Antony Lewis » February 06 2007

Thanks, but actually that paper cites Wild quoting 2.85e−15/s.

However the 2.869e-15/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!)

Post Reply