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    1) Radioisotopes such as aluminum -26, which is believed to have been present in the solar system when earth was formed but can no longer be detected, are known as extinct radionuclides. The half-life for the decay of aluminum -26 is 7.20 x 10 ^5 years.
    How many years did it take for 99.99% of the aluminum -26 to decay? If Earth was formed 4.6 x10^9 years ago, what percentage of the aluminum-26 present when the solar system was formed is still present today?

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    Solution Preview

    N(t)= N(0) exp (-lambda t)
    N(t)= Amount at time t
    N(0)= Amount at time 0
    lambda = decay constant
    t= time elapsed

    half life=T( 1/2)= 7.20 x 10 ^5 years.= 720000 years

    lambda =ln 2 / T( 1/2)= 9.627E-07 =0.693147/720000
    or 9.627 x 10 ^ -7 years ^ -1

    How many years did it take for 99.99% of the aluminum -26 to decay?

    N(t)= N(0) exp (-lambda t)
    or t= ln [N(0)/N(t)] / lambda

    for 99.99% of the aluminum -26 to ...

    Solution Summary

    The solution calculates the number of years it takes for 99.99% of the aluminum -26 to decay.