Quantum Physics Please answer correctly step-by-step with a clear handwriting. Thank you so much. 'Radiocarbon timing' I

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Quantum Physics
Please answer correctly step-by-step with a
clear handwriting. Thank you so much.
'Radiocarbon timing'
In the fossil sample, β-decays of the 14C nuclei occur
5.0 decays per second.
a) How many 14C nuclei are left in the
sample?
b) If the sample is 20,000 years old, how many
14C nuclei were originally present in the sample?
c) How much energy have decomposition reactions
produced in 20 000 years?
The right answers should be: a) 1,3 ·
1012, b) 1,5 ·
1013, c) 0,33 J