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Posted by on Wednesday, May 21, 2008 at 5:51am.

if 5/6th of a radioactive sample decay in 70 years and 1/6th remain. how can you find the half life without knowing the decay constant can you help?

  • physics - , Wednesday, May 21, 2008 at 6:41am

    The fraction (1/6) that remains after 70 years satisfies the relation:

    1/6 = 2^(-t/T),

    where T is the half life and t = 70 years.

    Take logs of both sides to solve for T. I'll use logs to base e but it doesn't matter

    -1.7918 = -70/T ln 2 = -48.52/T
    T = 27.1 years

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