Help with radiactive decay and radiation interactions hw

[lololai]

i need help with my nuc engineering homework due tomorrow. here is the link for hw1 in the course schedule. http://www.nuc.berkeley.edu/courses/classes/NE39/index.htm
if anyone can help me with problems 2 and 3, email me at lml841@juno.com asap! thanks a lot!

 

[Astronuc]

Nothing like waiting for the night before, eh?

For problem 2. One is given a source strength 2.3 Ci (1 Ci = 3.7E10 disintegrations/sec) of ⁶⁰Co (t_1/2=5.27 yrs), which is also the activity.

Activity A = $\lambda$ N, where $\lambda$ (the decay constant) = 0.69315/ t_1/2. Make sure you convert half-life to seconds if used with 1 Ci = 3.7E10 dps.

Therefore N (the number of atoms) = A / $\lambda$.

Using Avogadro's number and atomic mass, one can convert number of atoms to mass.

The activity A(t) as a function of time is given by A(t) = A_o $e^{-\lambda t}$. So one needs to find t when the activity has decreased to 1.4 Ci from 2.3 Ci.


For problem 3.

Look at class notes (Cross-section.pdf is a better explanation of the nuclear cross section concept covered during lecture 3):

FIGURE II.17. Monoenergetic parallel neutron beam incident normally on a thick target

and equations II.34 and II.35.