Problem #0147 Quantum Physics Problem #0149 Chapters Chapters

849.

Problem 54.66 (RHK)

A rock is found to contain 4.20 mg of and 2.00 mg of . We may assume that the rock contained no lead at formation, all the lead now present has arisen from the decay of the uranium. We have to find the age of the rock. The half-life of Uranium is

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A rock is found to contain 4.20 mg of and 2.00 mg of . Let the age of the rock be t y. We calculate the number of in 4.20 mg.

And, the number of in 2.00 mg will be

Let the number of in the rock when it was formed that is at be .

The half-life of is

An equivalent form of the radioactive decay law is

 

We note that

Therefore,

And,