Chemistry
posted by TlP .
Suppose a patient is given 140mg of I−131, a beta emitter with a halflife of 8.0 days.
Assuming that none of the I−131 is eliminated from the person's body in the first 4.0 hours of treatment, what is the exposure (in Ci) during those first four hours?
Express your answer using two significant figures.

k = 0.693/t_{1/2}
k = approx 0.09 but you should get a more accurate number.
Convert 140 mg to number of atoms initially (at time = 0)
Use ln(No/N) = kt to determine N = number of atoms after four hours.
The difference between initial and after 4 hours is atoms that decayed in 4 hours.
Then 3.7E10 decays per second = 1 Ci 
that is wrong Ci does not equal 1

Read what I wrote. I said 3.7E10 dps = 1 Ci, not that Ci = 1.