The half-life of oxygen -15 is 124 seconds. If a sample of oxygen -15 has an activity of 4000 becquerels, how many minutes will elapse before it reaches an acivity of 500 becquerels

1 answer

Calculate k from k = 0.693/t1/2 and substitute into the following:
ln(No/N) = kt
No = 4000
N = 500
solve for t, which will be in seconds, and convert to minutes.