Question

Given 1.00 grams of each of the following radioisotopes, Ca-37, U-238, P-32 and Rn-222,which would have the least remaining original isotopes after 100 years?
1) Ca-37
2) U-238
3) P-32
4) Rn-222

Answer 1

1) Ca-37, with a half-life of 181.1(10) ms.