Lesson Notes By Weeks and Term v4 - SHS 3
NUCLEAR PHYSICS
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NUCLEAR PHYSICS
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Subject: Physics
Class: SHS 3
Term: 1st Term
Week: 1
Grade code: 2.4.2.LI.3
Strand code: 4
Sub-strand code: 2
Content standard code: 2.4.2.CS.1
Indicator code: 2.4.2.LI.3
Theme: ATOMIC AND NUCLEAR PHYSICS
Subtheme: NUCLEAR PHYSICS
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Welcome, learners. Today, we delve into one of the most fascinating applications of nuclear physics: acting as a "time machine" to determine the age of ancient objects. Have you ever wondered how scientists know the age of a fossil discovered at an archaeological site in Ghana, like the Kintampo Stone Age sites, or determine how old an ancient wooden stool is? The answer lies in the predictable decay of radioactive elements, a process we call radiometric dating. We will focus on the most famous method, Carbon-14 dating, which allows us to date organic materials like bones, wood, and cloth.
A. The Principle of Carbon-14 Dating
All living things are made of carbon. Carbon exists mainly in two forms (isotopes) in our environment: Carbon-12 (¹²C): This is the most common and is stable. It does not decay. Carbon-14 (¹⁴C): This is a rare, radioactive isotope of carbon. It is unstable and decays over time.
How Carbon-14 is Formed and Absorbed: Cosmic rays (high-energy particles from space) strike nitrogen atoms (¹⁴N) in the upper atmosphere, converting them into Carbon-14 (¹⁴C). This ¹⁴C combines with oxygen to form radioactive carbon dioxide (¹⁴CO₂). Plants absorb this radioactive CO₂ during photosynthesis, incorporating ¹⁴C into their tissues. Animals eat these plants (or eat other animals that eat plants), and in doing so, they also take in ¹⁴C.
The "Clock" Starts at Death: While an organism is alive, it continuously exchanges carbon with its environment. This means the ratio of ¹⁴C to ¹²C in its body is constant and is the same as the ratio in the atmosphere.