Nuclear Reactions

Nuclear Reaction

There are two types of Nuclear reaction: Fission and Fusion. In both reactions, mass I converted to energy. Fission Reactions involves the splitting of a heavy nucleus to produce lighter nuclei. Fusion reactions involve the combining of light nuclei to produce a heavier nucleus. In reactions, the total mass of the product(s) is less than the total mass of the reactant(s). This mass defect is converted to energy.

The Energy derived from nuclear reactions is much greater than that formed in chemical reactions. The amount of energy produced by the conversions of mass can be calculated using Einstein’s equation

E =mc²

Where m is measured in kg, c is measured in m/s, and E in joules. The value of c is 3 x 10⁸ m/s, so c² is 9 x 10¹⁶. Using 1 kg of mass,

E = (1kg) (9 x 10¹⁶ m²/s²) = 9 x 10¹⁶ kg.m²/s²

= 9 x 10¹⁶ Joules

Fission Reactions

-          It begins with the capture of a slow-moving neutron by a nucleus of a heavy element such as uranium or plutonium. The resulting nucleus is very unstable and immediately “splits” or undergoes fission. The products of this fission are two nuclei of unequal mass, one or more neutrons, and a large amount of energy.

The equation for the reaction  is

¹₀n + ²³⁵₉₂U →  ⁹²₃₆Kr + ¹⁴¹₅₆Ba  +  3¹₀n + energy

This large amount of energy released in this equation is from the small loss of mass during the fission reaction.

One important feature of a fission reaction is the production of neutrons. These neutrons can become reactants to be captured by other U-235 nuclei, which in turn undergo fission and release more neutrons. This is known as a chain reaction, in which one reactant is the cause for further similar reactions. When this kind of reaction is not controlled, the energy is released in one explosive burst. This is the principle used in nuclear bomb.

There are methods by which the rate of a chain reaction can be controlled by limiting the neutrons that are allowed to react with U-235 nuclei. These controlled reactions produce a constant release of energy. They are carried out in nuclear reactors.

The fission products of U-235 presented in the figure is not a simple reaction. The fission of U-235 splits in different ways and produces more than 200 isotopes of 35 different elements. Many of these isotopes are unstable and are therefore radioactive. The radiation associated with these “by products” and the handling and disposal of these hazardous wastes are the major disadvantages of the use of nuclear energy.

Fusion Reactions

Nuclear Fusion combines smaller nuclei into a larger nuclei. It is the opposite of nuclear fission. The mass defect in the fusion of light nuclei produces tremendous energy which can be used for electric power. This can duplicate the furnace of the Sun here on Earth. Nuclear fusion holds great promise for inexpensive, safe, and clean nuclear power. The hydrogen isotopes that are needed as fuels are readily available. The reaction produces every little hazardous waste, compared with the products of fission reactions.

Some possible fusion reactions being used in experimental stage include:

²₁H + ²₁H → ⁴₂He  +  ⁰₁n + E

This is called the deuterium-tritium or DT reaction. Because tritium³₁H  has a very short half-life, this is produced as needed by bombarding deuteride (LiH) with neutrons.

Deuterium-deuterium (DD) reactions require high temperatures (100,000,000 K) and high activation energies to start the reaction because the electrical repulsion between the nuclei of like charges. Because of the high temperature involved, they are called thermonuclear process. This is also the reaction for hydrogen bomb.

²₁H + ²₁H → ⁴₂He + E