Radioactivity

RADIOACTIVITY

In the binding energy curve, the stability of the nucleus that has Z > 82 starts to decrease and these nuclei are called unstable nuclei. Some of the unstable nuclei decay naturally by emitting some kind of particles to form a stable nucleus. The elements of atomic number Z > 82 and isotopes of lighter nuclei belong to naturally-occurring radioactive nuclei. Each of these radioactive nuclei decays to another nucleus by the emission of ⁴₂He nucleus ( α -decay) or electron or positron (α-decay) or gamma rays ( β - decay).

The phenomenon of spontaneous emission of highly penetrating radiations such as α, β and γ rays by an element is called radioactivity and the substances which emit these radiations are called radioactive elements. These radioactive elements can be heavy elements (Z > 82), isotopes of lighter and heavy elements and these isotopes are called radioisotopes. For example, carbon isotope ¹⁴₆C is radioactive but ¹²₆C is not.

Radioisotopes have a variety of applications such as carbon dating, cancer treatment, etc. When radioactive nucleus undergoes decay, the mass of the system decreases – that is, the mass of the initial nucleus before decay is always greater than the sum of the mass of the final nucleus and that of the emitted particle. When this difference in mass ∆m < 0 , it appears as the energy according to Einstein’s relation E = |∆m| c² .

The phenomenon of radioactivity was first discovered by Henri Becquerel in 1896. Later, Marie Curie and her husband Pierre Curie did a series of experiments in detail to understand the phenomenon of radioactivity. In India, Saha Institute of Nuclear Physics (SINP), Kolkata is the premier institute pursuing active research in nuclear physics.

During early days of nuclear physics research, the term ‘radiation’ was used to denote the emanations from radioactive nuclei. Now we know that α rays are in fact ₂⁴He nuclei and β rays are electrons or positrons. Certainly, they are not electromagnetic radiation. The γ ray alone is electromagnetic radiation.