Q1(i). Carbon-14 dating of wood

Answer in brief

Radiocarbon dating estimates time since carbon exchange ceased from the remaining ¹⁴C activity. Wood retains carbon fixed by a living tree and becomes a decay clock after death.

Key points

• Atmospheric ¹⁴C forms mainly by ¹⁴N(n,p)¹⁴C and enters CO₂. Photosynthesis incorporates this carbon into growing wood.
• During life, exchange with the environment maintains a carbon-isotope ratio related to the surroundings. After death, further exchange largely stops.
• ¹⁴C undergoes β⁻ decay: ¹⁴C → ¹⁴N + e⁻ + antineutrino. The conventional physical half-life is about 5730 years.
• With initial and present specific activities A₀ and A, t = (t₁/₂/ln 2) ln(A₀/A).
• Contamination, changes in atmospheric ¹⁴C and old wood affect the result; calendar dates require calibration.