I am the Science department head at Guildford Park Secondary School located in Surrey, BC, Canada. I have been the Sr. Chemistry teacher here since 2007 and have pursued a B.Sc.(University of British Columbia) and M.Sc. (Simon Fraser University) in the field of Analytical Chemistry.
The half-life for the radioactive decay of U-238 is 4.5 billion years
and is independent of initial concentration. How long will it take
for 10% of the U-238 atoms in a sample of U-238 to decay? If a
sample of U-238 initially contained 1.5 * 1018 atoms when the
universe was formed 13.8 billion years ago, how many U-238
atoms does it contain today?