An atom is the smallest unit of an element. Each atom consists of a central nucleus that is surrounded by one or more negatively charged electrons. Electrons are continuously residing in fixed orbits around the nucleus. The central nucleus is made up of two subatomic particles such as protons and neutrons. Protons are positively charged, and neutrons have no charge at all. Isotopes are the different types of atoms of an element with the same number of protons and electrons but different numbers of neutrons. Isotopes can be categorized as stable and unstable isotopes. Unstable isotopes have unstable nuclei, and they are radioactive. They are known as radioactive isotopes or radioisotopes. In this article, we will learn about radioactive isotopes, the stability of the nucleus, half-life, etc.

Radioactive isotopes are the unstable form of an element that emits radiation to attain a more stable form. These isotopes have unstable nuclei, and that’s why they exhibit the phenomenon of radioactivity. Radioactivity is the phenomenon of disintegration of unstable atomic nuclei into comparatively lighter ones to form more energetically stable atomic nuclei. Different levels of radiation are emitted out of the unstable nucleus of an atom, and energy is lost during this phenomenon.

For instance, uranium and thorium are naturally occurring radioactive isotopes. Hydrogen is the lightest element and has three isotopes protium, deuterium, and tritium. Out of these isotopes, tritium is radioactive.

It refers to the stability of the nucleus of an atom. There are two driving forces at work inside the nucleus; strong nuclear force and electrostatic force. The strong nuclear force refers to the force of attraction that keeps the subatomic particles held together, and electrostatic force is the force of repulsion between two like charged particles. Positively charged protons repel each other due to this electrostatic force which is overcome by the strong nuclear force.

Neutrons have no charge. Still, they are important for stabilizing the nucleus. If the strong nuclear force between the nucleons is less than the electrostatic repulsion, it makes the nucleus unstable and emits radiation.

The stability of the nucleus depends on the number of protons and neutrons inside the nucleus. Nucleons with high binding energy are stable. Thus, the stability of an isotope can be determined by calculating the ratio of neutrons to protons (N/Z) present in a nucleus. Most of the stale nuclei have this ratio of more than one. All the elements that have atomic numbers more than 82 are unstable irrespective of the number of neutrons. Due to this reason, the atoms of uranium and plutonium are extremely unstable and emit lots of radiation. The emitted radiations are energetic and can be of different types, most often alpha, beta, and gamma rays. 

The half-life can be defined as the time taken for the concentration of given reactants to reach half of its initial concentration. In other words, the half-life of a radioactive isotope is the amount of time it takes for one-half of that isotope to decay. It is denoted by using the symbol “[math]t 1/2[/math]” and is usually expressed in seconds. The half-life is constant for first-order reactions; it is unaffected by conditions and is independent of the initial concentration of the isotope.

Radioisotopes with short half-lives tend to decay quickly, which makes them useful for diagnostic purposes, and others with long half-lives are suitable for therapeutic purposes. Radioactive isotopes are crucial in imaging the interior of the body. For instance, technetium-99m has a half-life of around 6 hours and is extensively used in imaging the brain, thyroid, bones, blood, and many other organs. Iodine-131 is found effective in cancer treatment. Another important radioisotope is carbon-14, which is less expensive to use in a breath test to detect the ulcer-causing bacteria Heliobacter pylori.