In nature, there are no living cells immune to radiation and there hardly exists a radiation free place. each person living on
earth is exposed to radiation originating from cosmic rays, radio active sources or artifical sources of daily life. 78% of the public doze is caused by the natural sources, 20.7% by medical irradiators and the rest is caused by occupational irradiators and artificial sources It should be noted that these numbers may show little variations and are expected to be location dependent.