Radiation: background, 259 biological effects

Altmann H, Tuschl H (1978) DNA repair investigations in lymphocytes of persons living in elevated natural background radiation areas (Bad Gastein). In Late biological effects of ionizing radiation, vol I. IAEA, Vienna, pp 437-445... 

As with chemical toxicity, there is no question that high doses of radiation cause biological damage. However, as discussed in Section 5.3.8, there are two models for the effects of radiation at low doses and we don t know with certainty if there is a low dose (or threshold) below which no damage is done. Therefore, it becomes difficult to set acceptable radiation doses, particularly in the context of a natural background of radiation to which we are all necessarily exposed. In medicine, we have accepted the notion that the use of radioisotopes in the body and the use of X rays are warranted when the overall known benefits outweigh probable or certain negative side effects. 

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