Question

Explain Nuclear fusion.

Hint:

Contrast nuclear fusion with nuclear fission. Fusion combines light nuclei (e.g., H + H \(\to\) He), while fission splits a heavy nucleus (e.g., Uranium \(\to\) Barium + Krypton). Both release enormous energy, but fusion generally releases more energy per nucleon and produces less long-lived radioactive waste.

Answer 1

Step 1: Understanding the Concept:
Nuclear fusion is the process that powers stars, including our Sun. It involves the merging of light nuclei, which results in a release of energy due to a phenomenon called mass defect.

Step 2: Detailed Explanation:
\begin{itemize} \item Process: In a fusion reaction, two light nuclei, such as isotopes of hydrogen (like deuterium and tritium), are forced together with enough energy to overcome their mutual electrostatic repulsion (the Coulomb barrier). Once they are close enough, the attractive strong nuclear force takes over and fuses them into a single, heavier nucleus (like helium).
\item Energy Release: The key to energy release is that the mass of the resulting heavier nucleus is slightly less than the sum of the masses of the original light nuclei. This difference in mass (\(\Delta m\)), known as the mass defect, is converted into a tremendous amount of energy (\(E\)) according to Albert Einstein's mass-energy equivalence principle, \(E = \Delta m c^2\), where \(c\) is the speed of light.
\item Conditions Required: Such reactions require extreme conditions of temperature (on the order of millions of degrees Celsius) and pressure. These conditions, found in the cores of stars, create a state of matter called plasma where nuclei are stripped of their electrons and have enough kinetic energy to overcome their repulsion and fuse.
\item Example (D-T Fusion): A common example studied for terrestrial fusion reactors is the fusion of deuterium (\(^2_1\text{H}\) or D) and tritium (\(^3_1\text{H}\) or T):
\[ ^2_1\text{H} + ^3_1\text{H} \rightarrow ^4_2\text{He} + ^1_0\text{n} + 17.6 \, \text{MeV (Energy)} \] Here, a deuterium nucleus and a tritium nucleus fuse to form a helium nucleus and a neutron, releasing 17.6 million electron-volts of energy.
\end{itemize}

Step 3: Final Answer:
Nuclear fusion is a process where light atomic nuclei merge to form a heavier nucleus. This process releases a significant amount of energy because the final product has less mass than the initial reactants, with the lost mass being converted directly into energy. The process requires extremely high temperatures and pressures.