A radioactive source has a half-life of 60hours and an activity of 480Bq. Find its activity after 240 hours (2 marks)
The number of half-lives in 240 hours is 240 / 60 = 4 half-lives. Divide 480 by 2, 4 times (because that is the number of half lives to get to 240) so at 240hours the activity is 30Bq
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