1) The number of radioactive nuclei in a particular sample decreases over a period of 15 days to one-seventeenth the original number. What is the half-life (in days) of these nuclei?

Question

2) What is the activity of a sample of 14C that contains 1.22E+21 nuclei?

Answer 1

1) n(t) = No e^-kt
where n is number at t and No is starting number
when t = 15. n/No = 1/17 = .0588
so
.0588 = e^-15k
ln .0588 = -15 k
k = -2.833/-15 = .18888
so
what is t when n/No = 1/2 ??
.5 = e^-.18888 t
ln .5 = -.693 = -.18888 t
t = 3.67 days half life

Answer 2

Thanks a lot Damon
Is my answer for the second problem correct?