Question

Difficulty: MediumMass Defect and Binding Energy

A nitrogen nucleus 714N^{14}_{7}\text{N} has a nuclear mass of 13.9992 u13.9992\text{ u}. Given that the mass of a proton is 1.0073 u1.0073\text{ u} and the mass of a neutron is 1.0087 u1.0087\text{ u}, what is the total binding energy of the nucleus in MeV\text{MeV}? (Take 1 u=931 MeV1\text{ u} = 931\text{ MeV})

Answer: 105.02 MeV

Answer

The total binding energy of the 714N^{14}_{7}\text{N} nucleus is 105.02 MeV105.02\text{ MeV}.
The total binding energy is computed by finding the total rest mass of 7 protons and 7 neutrons (14.1120 u), subtracting the actual nuclear mass of Nitrogen-14 (13.9992 u) to obtain a mass defect of 0.1128 u, and converting this mass defect to energy by multiplying by 931 MeV/u, yielding 105.02 MeV.

Step-by-Step Solution

1
Determine the number of constituent protons and neutrons
Z=7Z = 7 protons and N=147=7N = 14 - 7 = 7 neutrons
The atomic number is 7 and the mass number is 14.
2
Calculate the total mass of the constituent nucleons
Mnucleons=(7×1.0073 u)+(7×1.0087 u)=7.0511 u+7.0609 u=14.1120 uM_{\text{nucleons}} = (7 \times 1.0073\text{ u}) + (7 \times 1.0087\text{ u}) = 7.0511\text{ u} + 7.0609\text{ u} = 14.1120\text{ u}
The sum of the individual rest masses of all isolated protons and neutrons.
3
Compute the mass defect
Δm=14.1120 u13.9992 u=0.1128 u\Delta m = 14.1120\text{ u} - 13.9992\text{ u} = 0.1128\text{ u}
Mass defect is the difference between total mass of isolated nucleons and the bound nuclear mass.
4
Convert the mass defect into energy in MeV
Eb=0.1128 u×931 MeV/u=105.0168 MeV105.02 MeVE_b = 0.1128\text{ u} \times 931\text{ MeV/u} = 105.0168\text{ MeV} \approx 105.02\text{ MeV}
Applying the mass-energy equivalence factor 1 u=931 MeV1\text{ u} = 931\text{ MeV}.

Key Concept

Mass Defect and Binding Energy
Estimated Time:2m 0s
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