Strontium90 is one of the products of the fission of uranium

Strontium-90 is one of the products of the fission of uranium-235. This strontium isotope is radioactive, with a half-life of 28.1 yr. Calculate how long it will take for 0.500 g of the isotope to be reduced to 0.150 g by decay.

The carbon-14 decay rate of a sample obtained from a young tree is 0.332 disintegration per second per gram of the sample. Another wood sample prepared from an object recovered at an archaeological excavation gives a decay rate of 0.129 disintegration per second per gram of the sample. What is the age of the object?

Solution

k = 0.693/28.1 = 0.02466, t = (1/0.02466) ln( 0.5/0.15) = 48.823,