# Answer to Question #18263 in Atomic and Nuclear Physics for Kami

Question #18263

A radioactive nucleus has a half-life of 5x10^8 years. Assuming that a sample of rock solidified right after the solar system formed, approximately what fraction of the radioactive element should be left in the rock today?

Expert's answer

if we assume that age of solar system is approximately4.5x10^8 years, then law of radioactive decay tells us

N=N_0*2^{-t/T_{1/2}} = N_0*2^{-4.5/5} = N_0 = 0.534.

Hence, it will left only 53.4% of primordial amount

N=N_0*2^{-t/T_{1/2}} = N_0*2^{-4.5/5} = N_0 = 0.534.

Hence, it will left only 53.4% of primordial amount

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