The halflife of radioactive strontium90 is approximately 27 years. In 1961, radioactive strontium90 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?
time = _________ years
Thank you!
time = _________ years
Thank you!

fraction remaining, f = 0.5^(t/h) , where h is the halflife
0.07 = 0.5^(t/27)
(t/27)*log 0.5 = log 0.07
t = 27*log 0.07 / log 0.5 = 103.59 ≈ 104 years <
0.07 = 0.5^(t/27)
(t/27)*log 0.5 = log 0.07
t = 27*log 0.07 / log 0.5 = 103.59 ≈ 104 years <