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15 December, 10:16

A 200-gram sample of a radioactive nuclide is left to decay for 60 hours. At the end of 60 hours, only 25 grams of the sample is left. What is the half-life of the nuclide sample?

60 hours

30 hours

40 hours

20 hours - - - > I think 20?

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  1. 15 December, 10:39
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    Half life is the time taken by a radioactive isotope to decay by half its original mass.

    The original mass is 200 g

    Time taken is 60 hours

    Final mass is 25 g

    Therefore;

    Final mass = Original mass * (1/2) ^n; where n is the number of half lives.

    25 = 200 (1/2) ^n

    1/8 = (1/2) ^n

    n = 3

    Three half lives = 60 hours

    1 half lives = 20 hours

    Therefore; the half life of the radioactive nucleus is 20 hours
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