posted by .

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

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

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

Similar Questions

1. calc

The half-life of polonium is 139 days, but your sample will not be useful to you after 95 % of the radioactive nuclei present on the day the sample arrives has disintegrated. For about how many days after the sample arrives will you …
2. physics

Suppose 32000 radioactive nuclei are in a sample. About how many remain after two days if the half-life is 22 hrs?
3. Physics

University students, studying the activity of a particular radioactive isotope which had a half-life of 12.0 hours. If the original activity of the sample was 448 kBq, what would the activity be 3.00 days later?
4. math

An unknown radioactive element decays into non-radioactive substances. In 100 days the radioactivity of a sample decreases by 64 percent. a)(a) What is the half-life of the element?
5. phys

Although most natural potassium nuclei are stable 39K (93.3%) or 41K (6.7%) nuclei, about 0.0117% are radioactive 40K nuclei, which have a half-life of 1.26 billion years. What fraction of all the potassium nuclei in your body will …
6. physics

Radioactive nuclei are produced in an irradiated sample at the rate of 10 s-1. If the number in the sample builds up to a maximum of 1000, calculate the mean life and the half-life of the radioactive nuclei Using dN / dt = P - λ …
7. physics

116In nuclei are produced at the rate of 10 s-1. Calculate the maximum number of 116In nuclei (number in equilibrium) in the sample if the half-life of 116In is 54 m. So far I have come up with ... The half life = 54m x 60 s-1 = 3.24 …
8. Physics ...

116In nuclei are produced at the rate of 10 s-1. Calculate the maximum number of 116In nuclei (number in equilibrium) in the sample if the half-life of 116In is 54 m. So far I have come up with ... The half life = 54m x 60 s-1 = 3.24 …
9. physics

The number of radioactive nuclei present at the start of an experiment is 3.27 x 1015. The number present twenty days later is 7.66 x 1014. What is the half-life (in days) of the nuclei?
10. Physics

A radioactive isotope of Bismuth undergoes Beta Decay with a half-life of 22 days. How long (in days) will it take the Activity (A) of the sample to decrease to one-ninth of its original value?

More Similar Questions