Why do certain nuclei exhibit radioactive decay?

Certain nuclei exhibit radioactive decay because they are unstable and seek to reach a more stable state by emitting radiation.

Radioactive decay is a spontaneous process that occurs when an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves. This process is fundamental to nuclear physics and cosmology as it helps us understand the behaviour of unstable isotopes and the evolution of the universe.

The nucleus of an atom is made up of protons and neutrons. The forces between these particles are delicately balanced. If there are too many or too few neutrons relative to the number of protons, the nucleus becomes unstable. This instability is what drives radioactive decay. The nucleus will spontaneously change, or 'decay', into a more stable form. This decay process can involve the emission of alpha particles (two protons and two neutrons), beta particles (an electron or positron), or gamma rays (high-energy photons).

The rate at which a particular type of unstable nucleus decays is measured by its half-life, which is the time it takes for half of the unstable nuclei in a sample to decay. This is a constant property for each type of nucleus and is not affected by external conditions such as temperature or pressure.

The concept of radioactive decay is also crucial in various applications. For instance, it is used in radiometric dating techniques to determine the age of archaeological artefacts and geological samples. In medicine, radioactive isotopes are used in both the diagnosis and treatment of certain diseases. In nuclear power plants, the heat generated by radioactive decay is harnessed to produce electricity.

In summary, certain nuclei exhibit radioactive decay because they are unstable. This instability is due to an imbalance in the number of protons and neutrons within the nucleus. The nucleus seeks to reach a more stable state by emitting radiation, which can take the form of alpha particles, beta particles, or gamma rays. This process is spontaneous and occurs at a rate determined by the half-life of the nucleus.