Radioactive substance has a half life of 18 years. Decay rate remains constant how long will it before 95 percent of the sample has decayed?

Thanks,!(Nod)

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- Dec 15th 2009, 07:34 AMav8or91Radio active decay
Radioactive substance has a half life of 18 years. Decay rate remains constant how long will it before 95 percent of the sample has decayed?

Thanks,!(Nod) - Dec 15th 2009, 08:14 AMSoroban
Hello, av8or91!

Quote:

A radioactive substance has a half life of 18 years. Decay rate remains constant.

How long will it be before 95 percent of the sample has decayed?

. . where is the intial amount and .

Our function is: .

If 95% of the sample has decayed, then: .

We have: .

Take logs: .

. .