Radioactive decay

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Definitions: 

Half-life (T): The half-life of a radioactive isotope is the time taken  for the mass of the isotope to decrease to half its initial mass. (s)

Activity (A): The activity of a radioactive isotope is the number of nuclei of the isotope to decay per second. (Bq)

Decay constant (λ): The decay constant (λ) is the probability of an individual nucleus decaying per second. (s^-1)

The energy transfer per second from a radioactive source = AE (W)

Uses for radioactive decay: 

Carbon dating: Living plants contain small amount of carbon-14 with is created in the atmosphere by cosmic rays knocking out neutrons from nitrogen-14 nuclei. 

CO2 is taken up by the plant during photosynthesis and some of this CO2 contains carbon-14. Carbon-14 has a half-life of 5570 years so does not decay a lot during the plants lifetime. Once the plant has died, it no longer takes in CO2 so the proportion of C-14 decreases in the dead plant as the C-14 nuclei decays. This allows us to calculate the age.

Assumptions: The rate of production of C-14 is constant

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