Nuclear Fusion and Differences between Fission and Fusion

Nuclear Fusion

Nuclear fusion is a process in which two or lighter nuclei combine or fuse together to form a heavier and stable nuclide. The difference in mass (Dm) resulting in the process is converted into energy according to Einstein’s mass-energy relation DE = Dmc² which is released during fusion reaction. Example: The fusion of deuterium nuclei into a helium nucleus.

$$ _1H^2 + _1H^2 \rightarrow _2He^4 + \text {energy} $$

The fusion Reaction

Fusion reactions constitute the fundamental energy source of stars, including the sun. Hydrogen burning initiates the fusion energy source of stars and leads to the formation of helium. Generation of fusion energy for practical use also relies on fusion reactions between the lightest elements that burn to form helium. In fact, the heavy isotopes of hydrogen-deuterium and tritium react more efficiently with each other, and when they do undergo fusion, they yield more energy per reaction than do two hydrogen nuclei.

Reaction Energy

The difference between the masses before and afte1\20r the reaction corresponds to the reaction energy, according to the mass-energy relation. If initial particles A and B interact to produce final particles C and D, the reaction energy Q is defined as

$$ Q = (M_A + M_B – M_c – M_D)c^2 $$

When Q is positive, total mass decreases and the total kinetic energy increases which is called an exoergic reaction. When Q is negative, total mass increases and the total kinetic energy decreases which is called an endoergic reaction.

Differences between Fission and Fusion

Thermonuclear Reactions

The process of nuclear fusion requires a very high temperature, the nuclear fusion reactions are called thermonuclear reactions and the energy released is termed as the thermonuclear energy.

Controlled Thermonuclear Reactions

The fusion reaction can be controlled and can be used for the constructive purpose. Nuclear fusion reaction requires high temperature and ordinary metallic container vaporizes under the bombardment of such high temperature. So for controlled fusion especial container is designed to hold high temperature. At high temperature during fusion, electrons collide with each other violently and result into fully ionized gas called plasma. The plasma is an assembly of light nuclei like protons, deuterons, tritium and electrons moving rapidly in all directions. Since ordinary material wall cannot hold such plasma at a high temperature, attempts have been made to design a special type of magnetic bottle to hold such plasma matter. In such a process, the plasma is compressed and a very high temperature suitable for nuclear fusion is expected to be developed.

Nuclear fusion is suitable due to following ways:

1. Hydrogen is available everywhere on this planet in various forms.
2. The energy released per unit mass is very high.
3. It leaves no radioactive waste.

Reference

Manu Kumar Khatry, Manoj Kumar Thapa, Bhesha Raj Adhikari, Arjun Kumar Gautam, Parashu Ram Poudel.Principle of Physics. Kathmandu: Ayam publication PVT LTD, 2010.

S.K. Gautam, J.M. Pradhan. A text Book of Physics. Kathmandu: Surya Publication, 2003.