她测量了这两个元素放射性的总量和原子性质，感觉到物质的放射性是同放射性元素的总量成比例的。

She named the other radium. She measured the amount of radioactivity, an atomic property, and felt that the radioactivity was proportional to the amount of the element.

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又如，某种放射性物质可能正在以已知的速度进行衰变，需要我们确定在给定的时间后遗留物质的总量。

Or a radioactive substance may be disintegrating at a known rate and we may be required to determine the amount of material present after a given time.

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