A sample of Hydrogen-3 has a half-life of 12 years and contains 2400 atoms. Calculate the number of atoms that was present in the sample 48 years ago

38400 atoms

Explanation:

The half - life is the time taken for a radioactive material to decay by half. When the half-life time elapses, a material becomes halved.  

  Since the half-life is 12yrs;

    number of atoms  now = 2400atoms

Unknown:

Number of atoms in the sample 48yrs ago;

Solution:

   In 48yrs, we have 4 half-life counts:

         Last 12yrs;

                     2(2400) = 4800atoms

       Last 24yrs

                       2(4800) = 9600 atoms

      Last 36yrs

                    2(9600) = 19200 atoms

       Last 48yrs

                    2(19200) = 38400 atoms