Homework 7 Solutions

Within 02 r the h abundance drops and he increases

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Unformatted text preview: is higher abundance due in part to gravita%onal seJling. Within 0.2 R the H abundance drops and He increases due to nuclear fusion, which is more prolific in the core. The inversion within 0.07 R is the consequence of the Sun’s cumula%ve fusion reac%ons which have eaten up about 50% of the core H. 3He is a rare isotope so barely present in the outer parts of the Sun but is created (and destroyed) in the nuclear fusing regions. At the edge of the core the 3He abundance peaks up due to the slow weak reac%on 2H + 1H -­‐> 3He + e+ + νe, which requires less energy than the 3He + 3He -­‐> 4He + 1H + 1H reac%on due to reduced Coulomb repulsion. In the low temperature boundary of the core, the former reac%on is able to produce a liJle more 3He than is destroyed by the laJer, and the balance results in a reservoir of 3He. As we get closer to the center of the Sun, the laJer r...
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