Example 1
Deuterium (A=2,Z=1) and tritium (A=3,Z=1) fuse into helium−4(A=4,Z=2) and one particle. Identify the particle.
Initial totals are A=5 and Z=2. After helium−4, the remaining particle has A=1 and Z=0: a neutron.
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Year 11 · SACE Stage 1
Fusion and nuclear-reaction balances
Balance fusion reactions and calculate released energy under supplied assumptions.
Method and worked examples
Fusion joins light nuclei into heavier products. Positive nuclei repel electrically, so sufficiently energetic close encounters and quantum processes are needed for fusion; high-temperature plasmas provide suitable conditions in stars and fusion systems. Not every fusion reaction releases energy. For the light-nucleus reactions used here, a positive difference between total reactant and product rest mass corresponds to released energy.
Balance total nucleon number and electric charge, including emitted neutrons or other particles. Then calculate E=Δmc2 using supplied complete masses. Fission splits a heavy nucleus; fusion combines light nuclei. Sustained energy production additionally requires reaction conditions, confinement and energy balance. A positive energy per reaction alone does not establish that an entire power system delivers net useful electricity.
Example 1
Example 2
A fusion reaction has reactant rest mass 8.36×10−27kg and product rest mass 8.33×10−27kg. Use c=3.00×108m/s.
Δm=0.03×10−27=3.0×10−29kg. E=Δmc2=2.7×10−12J per reaction.
Watch out: Reaction energy must be distinguished from energy needed for heating, confinement, cooling and conversion in the whole system.