Radiation doses to humans may be characterized as low-level if they are comparable to natural background levels.
对人类的放射剂量如果与自然环境辐射水平相比属低水平。
It is believed that such a level is of no significance to human health having regard to natural background levels.
令人信服的是，考虑到自然本底值，这样小的放射水平对人体健康是无关紧要的。
The results show that the radioactivity level of varied water bod-ies of the city was within normal natural background.
调查结果表明，上海市各类水体中天然放射性核素浓度属正常本底水平。
The results show that the radioactivity level of varied water bodies of the region was within normal natural background.
调查结果表明，宁夏回族自治区水体中天然放射性核素浓度属正常本底水平。
The results show that the radioactivity level of varied water bodies of the region was within normal natural background.
调查结果表明，宁夏回族自治区水体中天然放射性核素浓度属正常本底水平。
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