Overburden had concealed the radioactivity.是什么意思？

Overburden had concealed the radioactivity.

覆盖层屏蔽掉了放射性.

overburden

vt. 装载过多，负担过多，使过劳；n. 过重的负担；

例句
Soil survey should be adopted in such soil overburden areas.
在此类土壤覆盖区应采用土壤测量.

had

v. 有（ have的过去式和过去分词 ），（亲属关系中）接受，拿，买到；

例句
He claimed that his parents had abandoned him...
他声称父母遗弃了他。

concealed

adj. 隐藏的；v. 隐藏，隐瞒，遮住( conceal的过去式和过去分词 )；

例句
His face will be discreetly concealed by camera angles.
通过调整照相机的角度，他的脸将被巧妙地遮住。

the

art. 指已提到的人（物），指说话人与听者已知的人（物），用于独一无二的事物前，与形容词最高级和序数词连用；

例句
He did have a real knowledge of the country...
他对该国的确知之甚多。

radioactivity

n. 放射（性），辐射能；

例句
At the surface, radioactivity of the conglomerates is locally as high as 30 X background.
在地表, 砾岩的局部地段的放射性高达30倍本底值.