Question

What is an example of the half-life of an isotope and describe the amount remaining and the time elapsed after five half-periods.?

Answer 1

A radio-active isotope will lose radio-activity at a certain rate. The time it takes to lose half its activity is called the half-life.

Explanation:

So every half-life period (`t_(1/2)`) the activity halves from the start of that period. So, after the second period, activity will be one half of one half, or one quarter of the original.

After 5 periods it will be `(1/2)^5=1/32`th

Example : Carbon-14, if left by itself, will have a half-life of 5730 years (wikipedia). This means that after 5 periods (=28650 years) it will have only 1/32th (about 3.1%) of its original activity left. This time/activity relation can be used to date organic material, as organisms take in carbon in a certain ratio of C-12 to C-14 while alive. When they die, the intake stops, but the radio-active decay of C-14 goes on.