Be sure to answer all parts. A freshly isolated sample of 90Y was found to have an activity of 2.2 × 105 disintegrations per minute at 1:00 p. m. on December 3, 2006. At 2:15 p. m. on December 17, 2006, its activity was measured again and found to be 5.8 × 103 disintegrations per minute. Calculate the half-life of 90Y. Enter your answer in scientific notation.

The half-life is  

Explanation:

From the question we are told that

     The sample is  90 Y

      The first  activity is    per minute

       The second  activity is    per minute

        The duration from 1:00 p.m. on December 3, 2006 to 2:15 p.m. on December 17, 2006   is

Converting to minutes we have  

The first order rate constant for this disintegrations can be mathematically represented  as

 Where is the rate constant

    Substituting values

So

The half life is mathematically represented as

So          

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