Question

Our book shows a radioactive decay series in which a sample thatstarts out as U-238 eventually winds up becoming non-radioactivePb-206. The half life for this process is extremely long, being4.51 x 10^9 years. Consider a radioactive mineral sample that is4.64 grams of U-238 and 1.22 grams of Pb-206 found in Colorado in1955. If all of the Pb-206 was once U-238, how old is this mineralsample? Hint: find "k" first.



1. about one billion years old

2. about 1.5 billion years old

3. about 2.3 billion years old

4. about 2.75 billion years old

5. about 7.2 billion years old