Atoms And Nuclei Question 383

Question: In a sample of rock, the ratio of 206Pb to 238U nuclei is found to be 0.5. The age in year of the rock is (given half-life of ,U238 is 4.5×109 years)

Options:

A) 2.25×109

B) 4.5×109ln3

C) 4.5×109ln(32)ln2

D) 2.25×109ln(32)

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Answer:

Correct Answer: C

Solution:

  • Suppose an initial radionuclide I decays to a final product F with a half- life T1/2.

At any time, N1=N0eλt Number of product nuclei =NF=N0NI NFNI=N0NINI=(N0NII)

N0NI=(1+NFNI)=1+0.5=1.5
,T1/2In(1.5)In2=4.5×109n(32)n2year



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