Talk:Wouthuysen–Field coupling

Coupling mechanism, 2nd paragraph

"The coupling between Lyman-alpha photons and the hyperfine states depends not on the intensity of the Lyman-alpha radiation, but on the shape of the spectrum in the vicinity of the Lyman-alpha transition."

Surely this should be, "The coupling... depends not only on the intensity..." For example, Furlanetto, Peng and Briggs (2006) state that,

"The Wouthuysen-Field coupling must depend on the total rate (per atom) at which Lyα photons are scattered within the gas, $P_{\alpha }=4\pi \chi _{\alpha }\int d\nu J_{\nu }(\nu )\phi _{\alpha }(\nu )$ where $\sigma _{\nu }=\chi _{\alpha }\phi _{\alpha }(\nu )$ is the local absorption cross section, $\chi _{\alpha }=(\pi e^{2}/m_{e}c)f_{\alpha }$, $f_{\alpha }=0.4162$ is the oscillator strength of the Lyα transition, $\phi _{\alpha }(\nu )$ is the Lyα absorption profile, and $J_{\nu }$ is the angle-averaged specific intensity of the background radiation field (by number, not energy)"

This direct dependence on the specific intensity (spectral radiance if you like) seems to contradict the line above.--92.28.198.33 (talk) 23:10, 12 April 2017 (UTC)