Radioactive dating animation

27-Dec-2015 22:19 by 7 Comments

Radioactive dating animation

We’re going to see what 'half-life' means and why radioactivity changes with time. It doesn’t depend on the size of the sample and it doesn’t change with time. So we imagine going in forward one half-life at a time from ZERO years: 10 years, 20 years, 30 years, etc.We’ll also see how carbon dating can be used to date ancient remains. If we had a bigger sample of the same isotope then the count would be higher, say 200 becquerels. Then we halve the count for each half-life: 100 Bq after 10 years; 50 Bq after 20 years; 25 Bq after 30 years So we can see the radioactivity would be 25 becquerels afer 30 years.

We can then compare it with the radioactivity of the same amount of carbon dioxide from the atmosphere. Even this kind of carbon dating can only be used to date things that were once alive and died less than about 60 000 years ago.

We can use the same idea to find out how long it would take for a sample with radioactivity 120 Bq to drop to 30 Bq. We can use radioactive decay to calculate the age of things.

The best-known technique is called ‘radiocarbon dating’ or just 'carbon dating'.

Remember that the carbon-14 decays all the time whether the thing's alive or not.

It's just that when it's living the carbon-14 is constantly replaced so the overall radioactivity stays constant. We don’t just stick a Geiger counter in front of it and hope for the best.

Carbon-14 is produced in the upper atmosphere by cosmic rays.

It is a beta emitter with a half-life of about 5600 years.

Animals and plants have similar amounts of radioactive isotopes, particularly potassium-40, another beta emitter.

We need to make sure that we’re only measuring the beta radiation from the carbon-14.

Carbon dating can be used to date things up to about 60 000 years old. Many people think that plants grow by taking food from the soil through their roots but this is not true. Animals eat plants (or other animals that eat plants) so animals are also mostly rearranged carbon dioxide.

All green plants make their own food in their leaves. A tiny fraction of carbon atoms are the radioactive isotope carbon-14.

This means a human adult has a radioactivity of around 3000-4000 becquerels due to carbon-14. When a living thing dies the cells are no longer replaced so no new carbon enters it.

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