After reading this article you will learn about the natural and man-made sources of environmental radiation.
Natural (Background) Environmental Radiation:
This includes cosmic rays that reach the surface of the earth from space and terrestrial radiations from radioactive elements present in the earth’s crust.
Many radioactive elements such as radium 224, uranium 235, uranium 238, thorium 232, radon 222, potassium 40 and carbon 14 occur in rocks, soil and water.
Man-Made Environmental Radiation:
This includes mining and refining of plutonium and thorium production and explosion of nuclear weapons, nuclear power plants, nuclear fuels and preparation of radioactive isotopes.
Production of nuclear weapons involves the tests of nuclear arms. These tests produce large amount of radioactive elements into the environment and make other materials also radioactive. They include strontium 90, cesium 137, iodine 131 and some others.
The radioactive materials are transformed into gases and fine particles which are carried to distant places by wind. When rain drops, the radioactive particles fall on the ground, it is called nuclear fallout. From the soil radioactive substances are taken by plants, thence they reach humans and animals through food chains.
Iodine 131 damages white blood corpuscles, bone marrow, spleen, lymph nodes, skin cancer, sterility and defective eye sight and may cause lung tumours. Strontium 90 accumulates in the bones and may cause bone cancer and tissue degeneration in most animals and man.
(a) Atomic Reactors and Nuclear Fuels:
The operation of a nuclear power plant releases large amounts of energy. This energy is used in large turbines, which produce electricity. Both the fuel elements and coolants contribute to radiation pollution. Wastes from atomic reactors also contain radioactive materials.
The biggest problem is the disposal of these radioactive wastes. If these wastes are not properly disposed off, can harm the living organisms wherever they may be dumped. Inert gases and halogens escape as vapours and cause pollution as they settle on land or reach surface waters with rain.
(b) Radio Isotopes:
Many radioactive isotopes such as 14C. 125I, 32P and their compounds are used in scientific research. Waste waters containing these radioactive materials reach water sources like rivers through the sewers. From water they enter human body through food chains.
(c) X-rays and Radiation Therapy:
Human beings also voluntarily receive radiation from diagnostic X-rays and radiation therapy for cancer.
(d) People working in power plants, nuclear reactors, fuel processors or living nearby are vulnerable to radiation exposure.
In radiation reactions it is important to know the amount of energy used and the yield of the products. Let us consider the units that have been employed for expressing the Dose, viz, the amount of energy absorbed.
These units are:
1. The Red:
The Rad is defined as follows:
1 Rad = Absorption of 100 ergs per gram of the substance = 10-5 jg-1 = 6.24 × 1013 eVg-1
2. The Gray:
The Gray (Gy) is the unit of dose in SI system. It is defined as follow- 1 Gray = 1 Kg-1 = 100 Rad
3. The Rontgen:
This unit is based on the ability of the radiation to ionize air.
The Rontgen (R)
Is defined as exposure to such a dose that would produce in 1 cm3 of dry air at STP, ions carrying 1 e.s.u of charge of either sign.
R (air) = 0.87 Rad = 8.7 × 1-3 Gy = 8.7 mGy
The dose rate:
The dose absorbed per second is expressed in units of Rad s-1 or Gy s-1.