Physics Form 5: Chapter 5 - Radioactivity

Introduction

In 1896, Bequerel, a French physicist discovered that crystals of Uranium salts emitted penetrating rays similar to X-rays which could fog photographic plates. Two years after this Pierre and Marie Currie discovered other elements: Polonium and Radium which had this property. The emission was known as Radioactivity.

 
The Stability of Nuclei

Protons and Netrons are held together in the nucleus of an atom by the strong-force. This force acts over a very short distance of about ~1 fm, (10^-15m) and over this short distance it can overcome the electromagnetic repulsion between the positively charged protons. Nuclei with radii that are within the range of the Strong force are stable. As atomic number increases the radius of the nucleus also increases and the element becomes unstable. This instablity manifests itself as the emission of particles or energy from the nucleus. The elements with atomic number greater than 82 are radioactive.

Radioactivity is the spontaneous and random emission of radioactive rays from unstable radioactive materials to become more stable material.

Spontaneous	Cannot be influenced by any physical factors such as temperature, pressure and time.
Random	Emission occurs at irregular intervals and does not occur at the same rate.

There are 3 types of radioactive rays:

• Alpha radiation
• Beta radiation
• Gamma radiation