Energy Sources in Stars (§10.3)
Energy Sources in Stars (§10.3)
Energy Sources in Stars (§10.3)
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Proton-Proton Cha<strong>in</strong>The previous nuclearreaction cha<strong>in</strong> (PPI) is notthe only way to convert H<strong>in</strong>to He.A second branch (PPII)In solar centre, 69% of 2 3 He comb<strong>in</strong>es withanother 2 3 He, but 31% can fuse with 2 4 He32He + 4 2He " 7 4Be + #eg last step:3 He + 3 He → 4 !He + 2p +can proceed differently ifthere is appreciable 4 Hepresent!!!!!7 4Be + e " # 7 3Li + $ e73Li + p + " 4 2He + 4 2HeA third branch (PPIII)In the Sun's core, a 4 7 Be nucleus can capturea p + <strong>in</strong>stead of an e " about 0.3% of the time.4Very unstable7 Be + p + " 5 8 B + #85B " 8 4Be + e + + # e8 Be " 4 2He + 4 2He4PPI + PPII + PPIII operatesimultaneously!!
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