# Half-life

• Aug 31st 2009, 08:31 PM
noles2188
Half-life
The half-life of radioactive strontium-90 is approximately 29 years. In 1963, radioactive strontium-90 was released into the atmosphere during testing of nuclear weapons, and was absorbed into people's bones. How many years does it take until only 7 percent of the original amount absorbed remains?
• Aug 31st 2009, 08:38 PM
CaptainBlack
Quote:

Originally Posted by noles2188
The half-life of radioactive strontium-90 is approximately 29 years. In 1963, radioactive strontium-90 was released into the atmosphere during testing of nuclear weapons, and was absorbed into people's bones. How many years does it take until only 7 percent of the original amount absorbed remains?

The fraction remaining after $\displaystyle t$ years is $\displaystyle 2^{-t/29}$, so you need to solve:

$\displaystyle 0.07= 2^{-t/29}$

CB
• Sep 1st 2009, 04:25 AM
HallsofIvy
I would have written it $\displaystyle \left( \frac{1}{2} \right)^{\frac{t}{29}} = 0.07$ but that's exactly the same thing.