'Radiocarbon dating' is used to find the age of formerly-living things. The halflife of carbon-14 is 5730 years. By how much will the original amount of ""^14C decrease after 5 halflives?

1 Answer
Simon M. ยท David G.
Nov 24, 2016

The amount of ""^14 C will be reduced to 1/32 (which is 1/2^5) of the original amount after 5 half lives.

Explanation:

Every half life period the amount of substance will reduce by half. For example after one half life of 5730 years the amount of ""^(14)C present within a sample will have halved.

If you start with 100 g of ""^(14)C, after one half life there will be 50 g left.
After 2 half lives (11460 years) there will be 25 g left.
After 3 half lives (17190 years) there will be 12.5 g left.
After 4 half lives (22920 years) there will be 6.25 g left
and after 5 half lives (28650 years) there will be 3.125 g left

This technique is only suitable for up to about 50 000 years as the quantities of ""^(14)C present in former living things is very small, and after ~8 half lives the quantity is too small.

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