What Is Meant By Radioactive Disintegration

Radioactive disintegration is a process of nuclear disintegration of a radioisotope in its effort to achieve a stable nucleus. We know that in the naturally available radioactive elements there are only two kinds of particles which could be ejected from its atoms:

1. The alpha (a) particle, which is really the nucleus of a Helium atom (⁴He) and carries away 4 mass particle and 2 atomic particles.
   
   _ZX^A - ₂a⁴ = _Z-2X^A
   
   Here X represents chemical symbol, Z is atomic number and A is mass number.
   
   
2. The other particle which could be ejected is beta (b) particle, which is an electron. It does not however, comes from an orbit, but from a neutron, which under certain circumstances, dissociates into a proton and an electron. The electron is not tolerated in the nucleus and is ejected immediately, but an extra positive charge (neutron replaced by a proton) is left in the nucleus. The new atom now has the same mass but the atomic number one higher than the old or previously possessed by it.
   
   _ZX^A - _-1b⁰ = _Z+1X^A

Uranium, Thorium and Radium are the best known naturally occuring radioactive elements. In 1934 it was documented that it was possible to create isotopes and radioisotopes by bombarding the stable elements with high energy subatomic particles. Except Hydrogen and Helium more than two isotopes have been created from every element by artificial manipulations. There are 21 isotopes of Iodine ranging from ¹¹⁹I to ¹³⁹I and out of these 20 are radioactive isotopes or radioisotopes except ¹²⁷I.

The artificially created radioactive isotopes or radioisotopes have the same radiations as those of natural ones. Some of them also emit protons or beta⁺ (b⁺) particles.

_ZX^A - ₊₁b⁰ = _Z-1X^A

Radioactive disintegration of radioisotopes results in the emission of only one type of above mentioned particles and radiation like x-rays called gamma (g) rays. The atoms of any particular radioactive element are destined to emit the same kind of radiation till its total disintegration; there is no way to switch on to any other type of radiation.

How The Structure Of Matter Is Associated With Radioactivity

We know that the matter is made up of elements. The smallest part of any element is its atom. Atoms are composed of a positively charged nucleus containing protons (positively charged subatomic particles) and neutrons (inert particles), and around the nucleus, there are orbital electrons (negatively charged subatomic particles). In 1896 Bacquerel discovered the phenomenon of radioactivity in the atoms of some elements. The mass of an atom is represented by its nucleus that is the sum of protons (positively charged subatomic particles) and neutrons (inert particles) in the nucleus. Each element has been allotted a chemical symbol and its atomic number is fixed. The number of electrons is always equal to the number of protons in the nucleus of an atom and this number stands for the atomic number of an atom. Mass of an electron is ¹/₁₈₀₀ of the mass of a proton on atomic scale. The atoms in some of the elements have natural variation in mass number and that made them unstable or radioactive.

Isotopes: Atoms of a particular element not have to be exactly alike in terms of mass number. In such atoms the things that must be alike are the number of protons (positively charged subatomic particles) in the nucleus or the nuclear charge and the number of orbital electrons (negatively charged subatomic particles). But the number of neutrons (inert particles) may vary and hence atomic mass may vary in a narrow range. Atoms of the same element with same atomic number but with different number of neutrons (inert particles) are called isotopes. A single chemical symbol of an element is not sufficient to represent an isotope. The chemical symbol along with a superscript at the upper left or right, depicting the mass number and lower left depicting the atomic number, represents an isotope; however, it is not necessary to mention atomic number to depict an isotope, as ⁵¹Cr represents an isotope of Chromium. Each element has a unique atomic number but the mass number may vary depending on the number of the isotopes of that element. An element generally has only one stable isotope.

Radioactivity: Majority of the elements found naturally have stable atoms. The atoms of the elements never change unless they are attacked with subatomic particles from outside; however, some of the atoms in some heavy elements are inherently unstable. The unstable atoms are called radioactive isotopes or radioisotopes. The nucleus of the radioactive atom or radioisotope undergoes disintegration with the ejection of tiny particle accompanied by electromagnetic radiation. After disintegration the rest of the material of the nucleus rearranges itself and becomes the nucleus of a different element.