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If a 20 gram sample of a radioactive substance has a half-life of 6000 years, how many grams would be present after 18000 years?

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  1. Radioactive decay law
    N =N₀exp(-λt)=
    =N₀exp(-ln2•t/T)=
    =20exp(-0.693•18000/6000) = 2.5 g

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