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Nuclear Reactions

Nuclear reactions are chemical reactions that take place in the nucleus of atoms of radioactive substances. it involves the protons and neutrons of the atoms.  

There are two types of nuclear reactions: fission and fusion.

Fission reaction occurs when a heavy nucleus is bombarded by slow moving neutrons. The neutrons are captured by the nucleus. The nucleus becomes heavier and less stable, and then breaks up into approximately equal halves, giving off great amount of energy.

²³⁵₉₂U + ¹₀n → fission products + 2 or 3 neutrons + energy.

This occurs when several nuclei are condensed to give a heavier and less stable nucleus.

For example: the three isotopes of hydrogen (¹₁H, ²₁H and ³₁H), normal hydrogen (also called protium), deuterium and tritium respectively, when condensed undergo radioactivity, releasing enormous amount of energy. In fact, the energy of the sun is believed to come about by the fusion of the three isotopes of hydrogen.

A nuclear equation represents a reaction in a single nucleus. It is balanced by considering the atomic and mass numbers on both sides of the equation. Notice that natural radioactive substances are those whose nuclei are heavy, unstable and therefore undergo decay. While artificial radioactive substances are those produced when the nuclei of stable atoms are bombarded by small particles, such as slow moving neutrons or alpha particles, thereby making them unstable and radioactive.

Example (1). ²³⁸₉₂U → ²³⁴₉₀Th + ⁴₂He

(2). ²³⁴₉₀Th → ²³⁴₉₁Pa + ⁰_–1β

These are natural radioactive isotopes, undergoing α and β decay respectively.

Note: on both sides of the equations, the atomic and mass numbers are balanced.

(3). ³¹₁₅P + ¹₀n → ³²₁₅P + γ

(4) ¹⁴₇N + ⁴₂He → ¹⁷₈O + ¹₁H .

The products (³²₁₅P and ¹⁷₈O ) are artificial isotopes. Both sides of the equations are balanced.

1. Enormous amount of energy is released in nuclear reactions. This may be converted to electricity, or used to power ships and submarines.

2. Radioactive nuclides are used in scientific research. Example, carbon dating – radioactive carbon is used in dating archeological objects.

3. Neutrons from radioactivity can be used to produce several radioactive isotopes.

4. Radiations from radioactivity can be used for radiography or auto-radiography of metals or other materials; in the industry for the polymerization of organic compounds to produce plastic materials; for the sterilization of food or pharmaceutical products; and for halogenation and oxidation processes.

5. Some radioactive isotopes are used in the direct treatment of certain diseases, such as cancer. A calculated amount of highly penetrating and high frequency gamma rays (γ) produced is directed onto cancerous cells to destroy them. However, uncontrolled exposures could also destroy healthy cells.

Note: * The discovery of radioactivity has faulted the idea in Dalton’s atomic theory, which states that atoms cannot be created nor destroyed – radioactive substances are destroyed and new substances are formed from them.

* From this lecture, the only idea in Dalton’s atomic theory which has not been faulted is the one that states that chemical combination is the union of atoms in definite numeric proportions. The others have been faulted by latter discoveries:

- the discovery of sub-atomic particles (i.e., electrons, protons and neutrons has faulted the idea of atoms being the smallest, indivisible particles of matter.

- the discovery of isotopy has faulted the idea of all atoms of the same element being alike in every way.

- the discovery of radioactivity and its effects, such as the ionization of gases and the disintegration or decay of certain atoms has faulted the idea of atoms being uncreative and indestructible.