Question

Difficulty: MediumNuclear Fission and Nuclear Fusion
Two deuterium nuclei (12H{^{2}_{1}\text{H}}) undergo nuclear fusion to form a helium-3 nucleus (23He{^{3}_{2}\text{He}}) and a neutron (01n{^{1}_{0}\text{n}}) according to the nuclear equation:
12H+12H23He+01n{^{2}_{1}\text{H}} + {^{2}_{1}\text{H}} \rightarrow {^{3}_{2}\text{He}} + {^{1}_{0}\text{n}}
Given the atomic mass values:
Mass of 12H=2.0141 u{^{2}_{1}\text{H}} = 2.0141\text{ u}
Mass of 23He=3.0160 u{^{3}_{2}\text{He}} = 3.0160\text{ u}
Mass of 01n=1.0087 u{^{1}_{0}\text{n}} = 1.0087\text{ u}
Taking 1 u=931.5 MeV1\text{ u} = 931.5\text{ MeV}, what is the energy released in this fusion reaction?
  1. A
    1.63 MeV1.63\text{ MeV}
  2. 3.26 MeV3.26\text{ MeV}Answer
  3. C
    5.23 MeV5.23\text{ MeV}
  4. D
    6.52 MeV6.52\text{ MeV}

Answer

The energy released in the fusion reaction is 3.26 MeV3.26\text{ MeV}.
The total mass of the reactants is 2×2.0141 u=4.0282 u2 \times 2.0141\text{ u} = 4.0282\text{ u}, while the total mass of the products is 3.0160 u+1.0087 u=4.0247 u3.0160\text{ u} + 1.0087\text{ u} = 4.0247\text{ u}. Subtracting product mass from reactant mass gives a mass defect Δm=0.0035 u\Delta m = 0.0035\text{ u}. Multiplying this mass defect by the energy equivalent factor of 931.5 MeV/u931.5\text{ MeV/u} yields 3.26 MeV3.26\text{ MeV}.

Step-by-Step Solution

1
Calculate the total mass of the reactants
Total reactant mass =2×2.0141 u=4.0282 u= 2 \times 2.0141\text{ u} = 4.0282\text{ u}
Two deuterium nuclei are fusing on the left side of the reaction equation.
2
Calculate the total mass of the products
Total product mass =3.0160 u+1.0087 u=4.0247 u= 3.0160\text{ u} + 1.0087\text{ u} = 4.0247\text{ u}
The reaction produces one helium-3 nucleus and one neutron.
3
Determine the mass defect (\Delta m)
\Delta m = 4.0282\text{ u} - 4.0247\text{ u} = 0.0035\text{ u}
Mass defect is the difference between total reactant mass and total product mass.
4
Calculate the energy released in MeV
E = 0.0035\text{ u} \times 931.5\text{ MeV/u} = 3.26025\text{ MeV} \approx 3.26\text{ MeV}
Multiplying the mass defect in atomic mass units (u) by 931.5 MeV/u931.5\text{ MeV/u} gives the total energy released.

Key Concept

Mass Defect and Energy Release in Nuclear Fusion
Estimated Time:1m 30s
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