# Question #9f663

##### 1 Answer

May 28, 2017

#### Answer:

This is called the **half-life** of the sample.

#### Explanation:

The most important thing to remember is that while half the sample decays after one half-life, the whole sample does *not* entirely decay after two half-lives. After the first half-life, the remaining half of the sample in effect acts as its own sample, independent of the decay product(s) intermingled with it. Half of this half decays during the second half-life.

So after two half-lives one-fourth of the sample remains, then one-eighth after three half-lives, and so on in a decreasing geometric progression, called *exponential decay*. In the case of carbon dating our instruments are sensitive enough to follow this decay for at least eight half-lives.