Question

Whether the total mass of nuclei increases, decreases or remains unchanged?

Hint:

In nuclear fusion, the total mass of the nuclei decreases, and the missing mass is converted into energy.

Answer 1

In the context of nuclear reactions, such as nuclear fission or fusion, the total mass of the nuclei involved can either increase, decrease, or remain unchanged, depending on the type of reaction. Let's discuss each scenario: 

1. Mass in Nuclear Fusion:

In nuclear fusion, two light atomic nuclei (such as hydrogen nuclei) combine to form a heavier nucleus (such as helium). In this process:

• The mass of the resulting nucleus is slightly less than the sum of the masses of the two original nuclei.
• This "missing" mass is converted into energy according to Einstein's equation \( E = mc^2 \), which is released as energy (usually in the form of heat and radiation).
• Thus, in nuclear fusion, the total mass of the products is slightly less than the total mass of the reactants, and this difference is released as energy.

2. Mass in Nuclear Fission:

In nuclear fission, a heavy nucleus (such as uranium-235 or plutonium-239) splits into two smaller nuclei, releasing energy. In this process:

• Similar to fusion, the mass of the products (the smaller nuclei and any released neutrons) is slightly less than the mass of the original nucleus.
• The difference in mass is also converted into energy and released according to \( E = mc^2 \).
• Thus, in nuclear fission, the total mass of the nuclei decreases, and the lost mass is released as energy.

3. Mass in Nuclear Decay:

In the case of radioactive decay, such as alpha, beta, or gamma decay, the mass of the parent nucleus is always slightly greater than the mass of the daughter nucleus or particles (like alpha particles, beta particles, etc.) produced. However, the mass difference is again converted into energy, often released as radiation.

4. Conclusion:

In both nuclear fusion and fission, the total mass of the nuclei involved decreases. The "lost" mass is converted into energy. However, in certain nuclear processes like stable reactions, the mass may remain unchanged. In general, for reactions involving the release of energy (fission, fusion), the total mass decreases, and the difference is manifested as energy. So, the total mass of nuclei typically decreases in nuclear reactions.