1. Half-life and Carbon Dating
7.2
Half-life and Carbon Dating

2. Today’s lesson Radioactive decay Half-life Half-life activity
Carbon dating
Radioisotope dating
Homework:
Textbook: p
Workbook: p
7.2: Half-life Worksheet

3. Recall from last lesson:
Unstable particles split apart, releasing smaller particles and energy
RADIOACTIVITY: the emission of energy or particles caused by the spontaneous disintegration of atomic nuclei
Radioactive decay: the process in which unstable nuclei lose energy by emitting radiation in the form of particles and energy

4. Radioactive decay
We can predict whether an atom will or will not decay based on whether the isotope is stable or not
However, we cannot predict precisely when the atom will decay because the decay event itself is spontaneous
We can calculate the probability of whether it will decay over a given time by examining large quantities of the radioactive atom and observing the pattern of decay
Half-life: ________________________________________________________
________________________________________________________

5. 0 Half-lives Example: Carbon
Carbon-14 undergoes radioactive decay to become nitrogen-14
0 Half-lives

6. 1 Half-life
2 Half-lives

7. 3 Half-lives
4 Half-lives

8. # Half-lives % 𝑪 𝟏𝟒 % 𝑵 𝟏𝟒 Ratio of 𝑪 𝟏𝟒 to 𝑵 𝟏𝟒
% 𝑪 𝟏𝟒
% 𝑵 𝟏𝟒
Ratio of 𝑪 𝟏𝟒 to 𝑵 𝟏𝟒 1 2 3 4
The half-life of Carbon-14 is 5730 years. This means after 5730 years, only half of a sample of Carbon-14 will remain.
How many years have passed if only 6.25% of a sample of Carbon-14 remains?

10. Carbon dating
The ratio between carbon-12 and carbon-14 in nature remains constant
Carbon-1298.93% STABLE
Carbon-141x 10 −10 % UNSTABLE
In a living organism, as the carbon-14 decays it is replenished by constantly eating new carbon (food)
However, once an organism dies the carbon-14 will decay and over time, will become less and less abundant compared to carbon-12
By comparing the ___________ between carbon-14 and carbon-12 in
organic remains, we can estimate _____________________________
__________ and, therefore, ___________________________________

11. Example
You are examining the remains of a beaver and you find that the proportion of carbon-14 to carbon-12 is only 12% of what you would find in a living beaver. How long has the beaver been dead?

12. Radioactive dating Carbon dating has limitations:
It can only be used to date ______________________________
Only accurate/useful for samples up to_______________________
Can use a similar idea to date other substances (e.g. Potassium-40 clock)