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Absorption Cross Sections (Mihalas Chapter 4). Bound-bound transitions (Einstein relations) Bound-free transitions (Einstein-Milne relations). Bound-Bound Transitions. Balance transitions between two levels Upwards absorption Downwards by spontaneous or stimulated emission. j. h ν ij. i.

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## Absorption Cross Sections (Mihalas Chapter 4)

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**Absorption Cross Sections(Mihalas Chapter 4)**Bound-bound transitions(Einstein relations)Bound-free transitions(Einstein-Milne relations)**Bound-Bound Transitions**• Balance transitions between two levels • Upwards absorption • Downwards by spontaneous or stimulated emission j hνij i**Energy Absorption Rate: Bij = Einstein coefficient for**absorption**Return Rates: Aji=Einstein coeff. spontaneous**em.Bji=Einstein coeff. stimulated em. (isotropic) (same direction as Iν)**Transition Rates**• Calculate or measure cross section**Transition Rates: Hydrogen**• H transitions n'→n**Einstein-Milne Relations:energy and velocity**Replace v dv increment in recombination term with this.**Denominator Term:Maxwell dist. ne(v); Saha eq. n0/n1**…….=1. ……**b-f Transfer Equation**T.E.: αν=pνhν , ne=Maxwellian, n0*/n1*=Saha, G(v)/pν above …

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