Question #67ffa

1 Answer
James W.
Dec 15, 2017

#139.32# seconds

Explanation:

If only 4% of the original sample remains, we know that:

#100/2^n = 4#, where #n# is the number of half-lives elapsed.

Rearranging this gives

#2^n = 25#
#n = log_2(25)#
#n = 4.64386# half lives

Since a half-life of Radium-221 is 30 seconds, we know it must have taken 4.6439*30 seconds for 96% to decay, which is #139.32# seconds.

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