Question

Compute the amount of energy that is released each time two silicon atoms fuse to make an iron atom (give your answer in MeV). How does this compare to the energy released by fusing four protons into a helium atom?

Answer 1

atomic mas of Silicon

M(Si) =28.0851 amu

atomic mass of iron is

M(Fe)=55.8452 amu

The mass defect is

Delta(M) = 2*28.0851 -55.8451 =0.3251 amu

1 amu = 1.66*10^-27 kg = 1.66*10^-27*(3*10^8)^2 J =1.494*10^-10 J =933.75 MeV

The energy released when fusing 2 atoms of Si is

E = 0.3251 *933.75 MeV =303.562 MeV

For protons fusing into He

M(proton) =1.00727 amu

M(He) =4.0026 amu

Mass defect is

Delta(M) =4*1.00727 -4.0026 =0.02648 amu

energy is

Delta(E) = 0.02648*933.75 MeV =24.7257 MeV

The energy of Silicon atoms fusing is 12 times bigger than for 4 protons fusing.