(\(\ce\)-240 has a half-life of 1 hour) Solution \(\ce\)-240 with a half life of only 1 hour.After 4 hours, only \(3.75 \: \text\) of our original \(60 \: \text\) sample would remain the *radioactive* isotope \(\ce\)-240.The half-lives of many **radioactive** isotopes have been determined and they have been found to range from extremely long half-lives of 10 billion years to extremely short half-lives of fractions of a second.The quantity of **radioactive** nuclei at any given time will decrease to half as much in one half-life.Subsequently, dramatic developments have taken place and determining the ages of minerals, rocks, archaeological and historical objects and so on is now routine.

All types of **radioactive** decay make a graph of the same general shape.

For example, if there were \(100 \: \text\) of \(\ce\)-251 in a sample at some time, after 800 years, there would be \(50 \: \text\) of \(\ce\)-251 remaining and after another 800 years (1600 years total), there would only be \(25 \: \text\) remaining.

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