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 belocation dependent.