Carbon dating is a technique for discovering the age of ancient once-living objects, such as bone, charcoal or a piece of wood, by measuring the amount of the radio-active isotope Carbon-14 ( $^{14}C$ ) that it contains.

Whilst plants and animals are alive their Carbon-14 remains constant, but when they die it decreases due to radioactive decay.

The amount, A, of Carbon-14 in an object t thousand years after it dies is given by the formula:


(The quantity A measures the rate of Carbon-14 atom disintegration and this is measured in “counts per minute per gram of carbon” cpm/g)

(a) Using a calculator, draw a table of values to show how the amount of Carbon-14 in an object varies with time. (Correct to 2 decimal places).

(b) Draw a graph of this data.

(c) Imagine that you have a fresh sample of tree wood. What is the rate of Carbon-14 atom disintegration?

(d) Imagine you have a sample of charcoal from Stonehenge and it is 4000 years old. What is the rate of Carbon-14 atom disintegration?

(e) Charcoal from the famous Lascaux caves in France gave a count of 2.34 cpm/g. Estimate the date of formation of the charcoal.

(f) Investigate "half-life" of a radioactive isotope.

One of the Enrichment tasks on this site
Last change to this page
Full Page history
Links to this page
Edit this page
  (with sufficient authority)
Change password
Recent changes
All pages