1. Half-Life & Carbon Dating pg. 621-625
LO: I understand how radioactive isotopes can be used to determine the age of matter.

2. Review of Radioactivity
Why are atoms unstable?
Unbalanced nuclear forces—Electrostatic Charge Repulsion & Strong Nuclear Force
The more protons in nucleus more neutrons needed to maintain stability.
Radioactive particles involved
Alpha Beta Gamma Neutron Positron
Types of Nuclear Reactions
Radioactive Decay
Nuclear Fusion—stars
Nuclear Fission—chain reactions (atomic bombs, etc.)

3. What we know about radioactivity
Radioactive (unstable) atoms exist everywhere:
Outer space bombardment into Earth’s atmosphere
Matter on Earth
Air
All atoms above Z=83 (Bismuth) are radioactive

4. What is half-life?
Half Life: The time it takes for half of the parent nuclide to decay to the daughter nuclide.
100%
50%
25%
1st HL
2nd HL
50 yrs

5. Half-life time duration for isotopes

6. Half-Life Problem Setup

7. Half-Life Examples
How long does it take for a 14.2 g sample of Radon to decay to g?

8. Half-Life Examples
Carbon-14 has a half-life of 5730 yrs. How old is the fossil if it contains only 12.5% of the Carbon-14 relative to living organisms?

9. Radiocarbon Dating
Radiocarbon Dating: A technique used to estimate the ages of fossils and artifacts due to the carbon-14 contained in them. Not useful for metals.
Carbon-14: A radioactive isotope formed from nitrogen bombardment in the atmosphere by a neutron particle.

11. Carbon-14 dating organisms
Plants take in Carbon-14 via photosynthesis
Living organisms eat plants which incorporate Carbon-14 into animal tissues
Upon death, the organism stops incorporating new Carbon-14 (half-life of 5730 yrs)
The amount (%) of Carbon-14 in the organic tissues indicates their age (relative to living organisms)
Not dependable when dating objects beyond 50,000 years

12. How old is the artifact?
Question: A wooden boat discovered near Egypt had a Carbon-14 content of approximately 12.5% of that found in living organisms. How old is the boat?

13. Solving Half-Life Problems

14. Solving Half-Life Problems
A radioactive sample contains 2.45 g of an isotope with a half-life of 3.8 days. How much of the isotope in grams remains after 11.4 days?

15. Solving Half-Life Problems
A 208 g sample of sodium-24 decays to 13.0 g of sodium-24 within 60.0 hours. What is the half-life of this radioactive isotope?