By scientific measures, the average American gets 620 millirems of radiation each year, half from background exposure, and that number needs to reach 100,000 to be worrisome.

科学测量结果显示，普通美国人每年受到的辐射为620毫仑目，其中一半属于天然本底辐射，而低于100,000毫仑目的辐射完全不需要担心。

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This is called background radiation and levels vary from place to place, though the average dose is fairly constant.

辐射强度会因地点而异，但平均辐射量实则大致相同。

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