Question

Difficulty: MediumMass Defect and Binding Energy

An oxygen nucleus 816O^{16}_{8}\text{O} has a measured nuclear mass of 15.9906 u15.9906\text{ u}. Given that the mass of a proton is 1.0078 u1.0078\text{ u} and the mass of a neutron is 1.0087 u1.0087\text{ u}, calculate the total binding energy of the nucleus in MeV\text{MeV}. (Take 1 u=931.5 MeV1\text{ u} = 931.5\text{ MeV})

Answer: 131.71 MeV

Answer

The total binding energy of the oxygen nucleus is 131.71 MeV131.71\text{ MeV}.
Summing the masses of 8 individual protons and 8 individual neutrons gives 16.1320 u16.1320\text{ u}. Subtracting the actual nuclear mass of 15.9906 u15.9906\text{ u} leaves a mass defect of 0.1414 u0.1414\text{ u}. Multiplying this mass defect by the equivalence constant 931.5 MeV/u931.5\text{ MeV/u} yields a total binding energy of 131.71 MeV131.71\text{ MeV}.

Step-by-Step Solution

1
Calculate the total combined mass of the free constituent nucleons
Mass of 8 protons + 8 neutrons = 8(1.0078 u)+8(1.0087 u)=8.0624 u+8.0696 u=16.1320 u8(1.0078\text{ u}) + 8(1.0087\text{ u}) = 8.0624\text{ u} + 8.0696\text{ u} = 16.1320\text{ u}
Oxygen-16 has Z=8Z = 8 protons and AZ=168=8A - Z = 16 - 8 = 8 neutrons.
2
Calculate the mass defect (Δm\Delta m)
Δm=16.1320 u15.9906 u=0.1414 u\Delta m = 16.1320\text{ u} - 15.9906\text{ u} = 0.1414\text{ u}
Mass defect is the difference between total constituent mass and actual nuclear mass.
3
Convert mass defect into total binding energy (EbE_b)
Eb=0.1414 u×931.5 MeV/u=131.7141 MeV131.71 MeVE_b = 0.1414\text{ u} \times 931.5\text{ MeV/u} = 131.7141\text{ MeV} \approx 131.71\text{ MeV}
Applying the energy equivalent factor of 931.5 MeV931.5\text{ MeV} per atomic mass unit.

Key Concept

Mass defect and nuclear binding energy equivalence
Rate this question