Which of the following is an example of nuclear fusion?
Formation of 4He from 2H
Understanding Nuclear Reactions: Fusion vs. Fission
Nuclear reactions involve changes within the nucleus of an atom, releasing significant amounts of energy. The two main types of nuclear reactions are nuclear fission and nuclear fusion.
- Nuclear Fission: This is the process where a heavy atomic nucleus splits into two or more lighter nuclei, often releasing neutrons and energy.
- Nuclear Fusion: This is the process where two or more lighter atomic nuclei combine to form a single heavier nucleus, releasing a large amount of energy. This process powers stars like our Sun.
Analyzing the Options for Nuclear Fusion Examples
Let's examine each provided option to determine which one represents nuclear fusion.
| Option | Reaction Description | Analysis | Type of Reaction |
|---|---|---|---|
| 1 | Formation of $^{144}$Ba and $^{89}$Kr from $^{235}$U | A heavy nucleus (Uranium-235) splits into lighter nuclei (Barium-144 and Krypton-89). This is characteristic of splitting a heavy atom. | Nuclear Fission |
| 2 | Formation of $^{235}$Pu from $^{235}$U | This involves a change in the element from Uranium (U) to Plutonium (Pu). While it involves nuclear transformation, it's typically through processes like neutron capture followed by beta decay, not fusion or simple fission into lighter elements. | Nuclear Transmutation (not fusion or simple fission) |
| 3 | Formation of $^{4}$He from $^{2}$H | This describes lighter nuclei (Deuterium, $^{2}$H) combining to form a heavier nucleus (Helium-4, $^{4}$He). Deuterium is a stable isotope of hydrogen. Forming Helium-4 from Deuterium involves the combination of light nuclei. A common reaction is the fusion of Deuterium and Tritium ($^{3}$H) to form Helium-4 and a neutron, or deuterium-deuterium reactions that can eventually lead to Helium isotopes. The core process is the combining of light nuclei. | Nuclear Fusion |
| 4 | Formation of water from hydrogen and oxygen | This is a chemical reaction where atoms rearrange to form molecules. It involves the sharing or exchange of electrons, not changes within the atomic nucleus. | Chemical Reaction |
Identifying the Correct Example of Nuclear Fusion
Based on the analysis, the formation of a heavier nucleus ($^{4}$He) from lighter nuclei ($^{2}$H) is the definition of nuclear fusion. Option 3 directly illustrates this principle. For instance, the Deuterium-Deuterium (D-D) fusion reactions can lead to Helium isotopes, or Deuterium can fuse with Tritium (which itself can be produced from D-D reactions or in a fusion reactor blanket) to produce Helium-4:
- $^{2}_{1}$H + $^{2}_{1}$H &rightarrow $^{3}_{2}$He + $^{1}_{0}$n + Energy
- $^{2}_{1}$H + $^{2}_{1}$H &rightarrow $^{3}_{1}$H + $^{1}_{1}$p + Energy
- $^{2}_{1}$H + $^{3}_{1}$H &rightarrow $^{4}_{2}$He + $^{1}_{0}$n + Energy
The option "Formation of $^{4}$He from $^{2}$H" represents processes where deuterium nuclei are involved in creating helium nuclei, which is a clear example of nuclear fusion.
Conclusion
Comparing the options, only the process described in option 3 involves the combination of lighter atomic nuclei to form a heavier one, which is the defining characteristic of nuclear fusion. The other options describe fission (splitting heavy nuclei), nuclear transmutation, or chemical reactions (forming molecules).
Revision Table: Key Nuclear Concepts
| Concept | Description | Example | Energy Release |
|---|---|---|---|
| Nuclear Fusion | Lighter nuclei combine to form a heavier nucleus. | $^{2}$H + $^{3}$H &rightarrow $^{4}$He + n | Very High |
| Nuclear Fission | Heavy nucleus splits into lighter nuclei. | $^{235}$U + n &rightarrow $^{141}$Ba + $^{92}$Kr + 3n | High |
| Chemical Reaction | Atoms rearrange by electron interactions (sharing/transfer). | 2H$_{2}$ + O$_{2}$ &rightarrow 2H$_{2}$O | Relatively Low |
Additional Information on Nuclear Fusion
Nuclear fusion is the energy source of stars, including our Sun. It requires extremely high temperatures and pressures to overcome the electrostatic repulsion between the positively charged nuclei and allow them to fuse. On Earth, achieving controlled nuclear fusion for power generation is a major scientific and engineering challenge. Reactions involving isotopes of hydrogen, such as Deuterium ($^{2}$H) and Tritium ($^{3}$H), are considered the most promising for terrestrial fusion reactors because they require less extreme conditions compared to fusing ordinary hydrogen.
Important Questions from Nuclei
The half-life of a radioactive substance is 10 days. How many days will it take to disintegrate 3/4 of its initial value?
If a matchbox of size 5 cm × 4 cm × 1 cm is filled with nuclear matter, what will be its expected mass? The density of nuclear matter is approximately 2.3 × 1017 kg m-3.
Which of the following is an example of nuclear fusion?
The half-life of a radioactive substance is 10 days. How many days will it take to disintegrate 3/4 of its initial value?
If a matchbox of size 5 cm × 4 cm × 1 cm is filled with nuclear matter, what will be its expected mass? The density of nuclear matter is approximately 2.3 × 1017 kg m-3.
