High doses of radiation are very harmful for human health. Do you know about the disaster ceated by the first atomic bombs which were exploded on two cities of Japan, Hiroshima and Nagasaki in 1945? They killed thousands of people and injured many more badly. The effects of exposure to intense radiation took years to appear as burns or cancer in human beings. After a couple of decades, the effect on babies born to mothers who were exposed to big doses of radiation, began to show up. Radiation is an important component of man's environment. We receive some radioactivity all the time from cosmic rays, from terrestrial and atmospheric environment and also from trace amounts of radioactive potassium, strontium and carbon present in the tissues of the body. At altitudes above 20 km, cosmic radiation is much stronger. Although, we do not find any immediate ill effects of this natural radiation on our health, one cannot be sure that they do not have long term effects.
Then there are man-made sources of radiation in modern era which have become an indispensable component of our life. Diagnostic medical and dental x-rays affect patients, doctors and technicians. T.V. sets, radioactive dial watches and luminous markers etc. add small amounts of radiation to man's environment, while nuclear power plant waste, if not disposed of properly, is a great risk to human health. Major hazards of radiation are testing of atomic and nuclear bombs. Radiation, like x-rays, gamma rays, alpha and beta particles penetrate the body tissues and injure them.
The extent of damage is related to the total dose of exposure. Higher doses affect immediately and are fatal. They affect the blood cells and soften the muscles. Acute radiation sickness is a well defined disease. Somewhat lower doses show delayed effects. They cause some cells to divide more rapidly than usual. 'Ibis leads to various forms of cancer like Leukaemia or other malignant tumors. Unfortunately, some of the damages are not recognisable within the life span of the exposed person, these will become manifest in the coming generations.