Posted by Melanie on .
Suppose a sample of Cesium137 with initial mass of 200 grams decays to a mass of 160 grams voer the course of 10 years.
Find the halflife of Cesium137 (Round to the nearest year)
How much Cesium137 is left in the sample after 60 years? Round to the nearest tenth of a gram.

algebra 
drwls,
If T is the half life,
(1/2)^(t/T) = 0.16/0.20 = 0.80
where t = 10 yr
(t/T) = 0.3219
T = 31 yr
After 60 yr, the fraction left is
(0.5)^(60/31) = 0.261
Amount left = 200*0.261 = 52.3 g