Americium-241 is used in some smoke detectors. It is an alpha emitter with a  half-life of 432 years. How long will it take in years for 38.0 %% of an Am-241 sample to decay?

239Pu is a nuclear waste byproduct with a half-life of 24,000 y. What fraction of the 239Pu present today will be present in 1000 y?

The isotope 208Tl undergoes decay with a half-life of 3.1 min.. (a) What isotope is produced by the decay?. (b) How long will it take for 99.0% of a sample of pure 208Tl to decay?. (c) What percentage of a sample of pure 208Tl remains un-decayed after 1.0 h?

A sample of rock was found to contain 8.23 mg of rubidium-87 and 0.47 mg of strontium-87.. (a) Calculate the age of the rock if the half-life of the decay of rubidium by emission is 4.71010 y. (b) If some S3887r was initially present in the rock, would the rock be younger, older, or the same age as the age calculated in (a)? Explain your answer.