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Is Radio Recombination Line Emission Isotropic?

-- Pradeep | June 21, 2019

Question:

Greetings.

Does Radio Recombination Line(RRL) spontaneous emission rate have angular dependence?.

Please consider a hypothetical spherical volume that has a uniform density of Rydberg hydrogen atoms. We assume that all the atoms in the spherical region are excited to a very large identical quantum state with a principal quantum number, say n=200 at t=0 (start of observation). Will the spontaneous emission rate of radio frequency(RF) photons leaving the surface of the hypothetical sphere be fairly constant (i.e. isotropic)?. Or will there be a certain region on the sphere surface at which the emission rate of RF photons is higher (i.e. anisotropic)?

Sir could you please provide your valuable guidance on the above query.

-- Pradeep

Answer:

Yes, in fact emission from a cloud of gas which contains hydrogen atoms which are in excited states, called radio recombination line emission, is isotropic. This is due to the fact that the strength of the emission from radio recombination lines is dictated by the spontaneous emission rate, which is dependent upon on the atomic dipole moment and some physical constants.

-- Jeff Mangum

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