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Question

A star converts all its hydrogen to helium, achieving a 100% helium composition. Next it converts the helium to carbon via the triple-alpha process,
4He+4He+4He12C+7.27 Mev
The mass of the star is 4.6×1032 kg, and it generates energy at the rate of 5.3×1030 W.How long will it take to convert all the helium to carbon at this rate?

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Solution

Fusion takes place deep within the sun is given by

411H42He+2e++2v+26.7MeV

If Q1 is the energy released by fusion of 1.0 kg of hydrogen, then

Q1=1000×6.023×1023×26.74MeV
=40.2×1026MeV

Again,during the fission of one nucleus of 235U, energy released is 200 MeV.
If Q2 be the energy released by the fission of 103 of 235U, then

Q2=1000×6.023×1023×200235MeV
=5.1×1026MeV

Q1Q2=40.2×10265.1×1026=7.88=8

SO, energy released per kg of fuel in fusion is nearly 8 times that in fission.

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