Question

Differentiate between nuclear fission and nuclear fusion, giving one example for each.

Hint:

Binding energy curve peak is near Iron ($^{56}\text{Fe}$, $\approx 8.75\text{ MeV/nucleon}$). Fission moves heavy nuclei leftward towards Iron, while fusion moves light nuclei rightward towards Iron, both releasing net energy.

Answer 1

Concept:
• Nuclear fission and nuclear fusion are nuclear reactions that release massive energy by transforming nuclei into configurations with higher binding energy per nucleon ($E_b/A$).

Step 1: Tabulate key differences

• Definition:
- Fission: Process in which a heavy unstable nucleus splits into two lighter medium-mass daughter nuclei upon absorbing a thermal neutron.
- Fusion: Process in which two light nuclei combine together at extremely high temperature and pressure to form a heavier, more stable nucleus.

• Temperature Requirement:
- Fission: Occurs readily at room temperature with slow (thermal) neutrons.
- Fusion: Requires extremely high temperatures ($\approx 10^7 - 10^8\text{ K}$) to overcome strong electrostatic Coulomb repulsion between positively charged nuclei.

• Energy per unit mass:
- Fission: Energy released per unit mass is relatively lower ($\approx 0.85\text{ MeV/nucleon}$).
- Fusion: Energy released per unit mass is significantly higher ($\approx 6.75\text{ MeV/nucleon}$).

• Radioactive Waste:
- Fission: Produces highly radioactive fission fragments and long-lived toxic nuclear waste.
- Fusion: Produces mostly non-radioactive stable products (like Helium), generating negligible radioactive waste.

Step 2: Examples
1. Nuclear Fission Example:
Neutron-induced fission of Uranium-235:
\[ \text{}^{235}_{92}\text{U} + \text{}^{1}_{0}\text{n} \longrightarrow \text{}^{141}_{56}\text{Ba} + \text{}^{92}_{36}\text{Kr} + 3 \text{}^{1}_{0}\text{n} + Q\text{ (\approx 200 MeV)} \]
2. Nuclear Fusion Example:
Proton-Proton cycle or Deuterium-Tritium fusion reaction:
\[ \text{}^{2}_{1}\text{H} + \text{}^{3}_{1}\text{H} \longrightarrow \text{}^{4}_{2}\text{He} + \text{}^{1}_{0}\text{n} + Q\text{ (17.6 MeV)} \]

Step 3: Conclusion
Fission involves splitting heavy nuclei at normal temperatures, whereas fusion involves combining light nuclei at ultra-high thermonuclear temperatures.