Another standard, Oxalic Acid II was prepared when stocks of HOx 1 began to dwindle. The ratio of the activity of Oxalic acid II to 1 is 1.29330.001 (the weighted mean) (Mann, 1983). There are other secondary radiocarbon standards, the most common is ANU (Australian National University) sucrose.

The ratio of the activity of sucrose with 0.95 Ox was first measured by Polach at 1.50070.0052 (Polach, 1976b:122).

What methods do they use and how do these methods work?

In this article, we will examine the methods by which scientists use radioactivity to determine the age of objects, most notably **carbon**-14 **dating**.

Radiocarbon *dating* (usually referred to simply as *carbon*-14 *dating*) is a radiometric *dating* method.

It uses the naturally occurring radioisotope *carbon*-14 (14C) to estimate the age of *carbon*-bearing materials up to about 58,000 to 62,000 years old.

But it is possible to measure the time taken for half of the nuclei in a *radioactive* material to decay.

This is called the half life of **radioactive** material or radioisotope.

It can also be defined as the time taken for the count rate of a sample of **radioactive** material to fall to half of its starting level.

The halflife of *carbon* 14 is 5730 ± 30 years, and the method of *dating* lies in trying to determine how much *carbon* 14 (the *radioactive* isotope of *carbon*) is present in the artifact and comparing it to levels currently present in the atmosphere.

Above is a graph that illustrates the relationship between how much **Carbon** 14 is left in a sample and how old it is.

*Carbon* *dating* has given archeologists a more accurate method by which they can determine the age of ancient artifacts.

Libby invented **carbon** **dating** for which he received the Nobel Prize in chemistry in 1960.

**Carbon** has two stable, nonradioactive isotopes: **carbon**-12 (12C) and **carbon**-13 (13C).

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