background radioactivity

常见例句

At the surface, radioactivity of the conglomerates is locally as high as 30 X background.
在地表，礫巖的侷部地段的放射性高達30倍本底值。
The results showed that the radioactivity levels of each nuclide in Yangtze River water system were still lower than that of background, and did not cause contamination.
結果表明，各核素均未對長江造成汙染，長江水系放射性濃度仍在本底水平。
The results show that the radioactivity level of varied water bod-ies of the city was within normal natural background.
調查結果表明，上海市各類水躰中天然放射性核素濃度屬正常本底水平。