United nation science committee of effect of atomic radiation ( unscear ) pointed out in its 1993 report : the collective dose from nature radiation exposure is 76 . 6 % of the total collective dose from all radiation exposure 联合国原子辐射效应科学委员会( unscear ) 1993年报告书指出:天然辐射产生的辐射照射集体剂量占总集体剂量的76 6 % 。