Half-Life & Carbon Dating pg. 621-625 LO: I understand how radioactive isotopes can be used to determine the age of matter.
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.)
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
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
Half-life time duration for isotopes
Half-Life Problem Setup
Half-Life Examples How long does it take for a 14.2 g sample of Radon to decay to 0.8875 g?
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?
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.
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
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?
Solving Half-Life Problems
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?
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?