# Homework Help: Radioactive Decay Chernobyl reactor accident

Tags:
1. Nov 3, 2015

Among the radioactive products emitted in the 1986 Chernobyl reactor accident were 131I ( t1/2 = 8.0 d) and 137Cs (t1/2 = 30 y). There are about five times as many 137Cs atoms as 131I atoms produced in fission. (a) Which isotope contributes the greater activity to the radiation cloud? Assume the reactor had been operating continuously for several days before the radiation was released. (b) How long after the original incident does it take for the two activities to become equal? (c) About 1% of fission events produce 131I, and each fission event releases an energy of about 200 MeV. Given a reactor of the Chernobyl size (1000 MW), calculate the activity in curies of 131I after 24 h of operation.

2. Relevant equations
t1/2 = 1/λ
Activity = λ*N(t)
N(t) = N0e-λt
3. The attempt at a solution
I believe i got the correct answers for parts A and B, but I am stuck on C. I have the equation Activity = λ*N(t), and N(t) = N0e-λt. I'm not sure how to find my value for N0. Any help is greatly appreciated. Thank you!

Last edited: Nov 3, 2015
2. Nov 4, 2015

### Alettix

From the power of the reactor and the energy of each fission event, you can find how many fission events occur in a given time, and from that how many 131I there are produced in that given time.