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3. A sample of a radioactive isotope is found to have an activity of 115.0 Bq immediately after
it is pulled from the reactor that formed it. Its activity 2 h 15 min later is measured to be
85.2 Bq.
(a) Calculate the decay constant 7 and the half-life t₁/2 of the sample.
(b) How many radioactive nuclei were there in the sample initially?

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