When radioactive substances emit energy in environment, it is known as radioactive pollution. Some of the radioactive elements occur as minerals on earth’s crust. Example – Uranium
There are four kinds of radiations
Alpha rays – These are fast moving positively charged particles. They can be interrupted by a sheet of paper.
Beta rays – The Beta rays are high speed negatively charged electrons. They can pass through paper but can be stopped by a piece of wood or by an Aluminium sheet of few millimeters.
Gamma rays – Gamma rays are high energy electromagnetic radiations that can be stopped by a concrete wall, lead slabs or water.
Neutron rays – They are produced in atoms bombs and nuclear reactors.
Major radiation hazard occurs on exposure to gamma and neutron rays.
The main source of radioactive pollution are either natural or man made.
Natural sources – Some materials from earth’s crust and environment emit radioactive radiations. These include isotopes of Potassium (K-40) and Carbon (C-14), Uranium, thorium and radium. These are very common in rocks, soil, air and water.
– Cosmic rays coming from the outer atmosphere. Its concentration depends upon the latitude and altitude.
– Radioactive substances like uranium, thorium and isotopes of potassium and carbon exist in small amount in human body. The value of emissions due to these substances is very low.
Man made sources – Radioactive wastes from nuclear power plants can cause a major destruction. The nuclear plants are made leak proof but a leakage may result in escaping of radionuclides in atmosphere, which is hazardous. Leakage in Three Mile Island nuclear plant in USA, in 1979 and melt down of Chernobyl nuclear power plant in USSR, in 1986 are examples of such accidents.
– Industrial and bio-medical wastes also contain hazardous radioactive substances.