Modern Physics 3 Caltec S.5

MODERN PHYSICS Nuclear Physics Radioactivity It is the spontaneous disintegration of unstable nuclei by emitting alpha particles, beta particles and gamma rays. The nuclei of some elements, like Uranium, Thorium, e.t.c are unstable and these undergo radioactive decay in order to gain stability. The new nucleus formed is known as a daughter nucleus Alpha particles () It is a helium atom with a mass number of 4 and atomic number of 2. Its properties: It is positively charged They are deflected by both magnetic and electric fields Alpha particles have a very high ionizing power in air They have low penetrating power and can be stopped by pieces of paper They cause fluorescence in some metals e.g. silver chloride and Zinc sulphide They have a slight effect on photographic plates Note:During alpha decay, the mass number decrease by 4 and atomic number decreases by 2 Example: Beta particles () Beta particles are electrons and their properties are: They are negatively charged They have a higher penetrating power compared with that of alpha particles They have a low ionizing power They are deflected by both magnetic and electric fields They have a negligible mass Note: During beta decay, mass number is not affected but the atomic number increases by one Example: Gamma rays (γ) These are the electromagnetic radiations, wave like in nature and travelling at the speed of light They have the following properties: They carry no charge , They are not reflected by both magnetic and electric field, They have a high penetrating power, They have a weak ionization potential. Note: Atomic number -: This is a number of protons in the nucleus of an atom Definition of terms: Atomic Number: It is the number of protons in the nucleus of an atom. Mass number: It is the number …