Fusion of Nuclei (Low A)
Nuclear fusion is the process in which two light atomic nuclei combine to form a heavier nucleus. This process releases a significant amount of energy, as seen in the fusion of hydrogen atoms into helium in the Sun.
A common example of a fusion reaction involves the isotopes of hydrogen, deuterium (2H) and tritium (3H), combining to form a helium nucleus:
2H + 3H → 4He + 1n + 17.6 MeV
In this reaction, the energy released is in the form of kinetic energy of the particles and radiation. The high energy (17.6 MeV) is due to the strong nuclear force binding the nucleons in the helium nucleus.
While fusion holds promise for producing large amounts of clean energy, creating and maintaining the high temperatures and pressures required for controlled fusion has proven to be a significant challenge. Currently, no fusion reactor has achieved net energy gain, but various projects, such as ITER (International Thermonuclear Experimental Reactor), continue to explore ways to make fusion a viable energy source.
Current Status of Fusion: While fusion reactions have been achieved in laboratories, the challenge remains to create a sustainable reaction where the energy produced is greater than the energy required to maintain the reaction. Scientists are hopeful that in the coming decades, fusion will play a major role in power generation.
Fission of Nuclei (Large A)
Nuclear fission is the process of splitting a heavy atomic nucleus, such as uranium-235 (235U), into two lighter nuclei, releasing a significant amount of energy. This process is harnessed in nuclear reactors for power generation.
When uranium-235 absorbs a neutron, it becomes unstable and splits into two smaller nuclei (called fission fragments), releasing energy and more neutrons that can trigger further fission reactions. A typical fission reaction looks like this:
235U + 1n → 92Kr + 141Ba + 31n + 200 MeV
The energy released during fission is primarily in the form of kinetic energy of the fission fragments and the emitted neutrons, as well as radiation. Fission is the process used in nuclear reactors to produce electricity.
The first controlled chain reaction using nuclear fission was achieved by Enrico Fermi and his team in 1942 at the University of Chicago. Since then, nuclear reactors have become an essential source of power, but concerns about radioactive waste, reactor safety, and nuclear proliferation remain significant challenges.
Fission Reactors: Modern nuclear reactors, such as pressurized water reactors (PWR) and boiling water reactors (BWR), harness the energy released by fission reactions to produce steam, which drives turbines and generates electricity. Despite its efficiency, nuclear fission has environmental concerns due to radioactive waste, which remains hazardous for thousands of years.