Peoples Physics Concepts

http://www.ck12.org Chapter 20. Radioactivity and Nuclear Physics

20.3 Carbon Dating

• Describe how carbon dating works.


• Solve for the age of an artifact using the carbon dating technique.

Students will develop an understanding of how carbon dating works and also learn to solve for the age of an artifact
using the carbon dating technique.

Key Equations

M=M 0 (

1

2

)

tt

H

The amount of massMof the substance surviving after an originalM 0 nuclei decay for timetwith a half-life oftH.

Guidance

Radioactive carbon datingis a technique that allows scientists to determine the era in which a sample of biological

material died. A small portion of the carbon we ingest every day is actually the radioactive isotope^14 C rather than

the usual^12 C. Since we ingest carbon every day until we die (we do this by eating plants; the plants do it through

photosynthesis), the amount of^14 C in us should begin to decrease from the moment we die. By analyzing the ratio

of the number of^14 C to^12 C atoms in dead carbon-based life forms (including cloth made from plants!), we can

determine how long ago the life form died.

Example 1

Question: The half-life of^239 Pu is 24,119 years. You have 31.25 micrograms left, and the sample you are studying
started with 2000 micrograms. How long has this rock been decaying?
Answer: We will use the equation for time and simply plug in the known values.

t=tH

lnNN 0

ln^12

=24119y

ln^312000.^25 μμgg

ln^12

= 144 ,700years

Watch this Explanation

MEDIA

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