Posted by Anonymous on .
Suppose 32000 radioactive nuclei are in a sample. About how many remain after two days if the halflife is 22 hrs? What is the initial activity of the sample in decays per minute?

physics 
drwls,
Two days is 48 hours or 2.18 halflives. The original number of radioactive nuclei, 2 days earlier, is higher by a factor 2^2.18 = 4.53, so there were N0 = 145,000 radioactive nuclei then.
There is a formula that relates activity per molecule (k) to half life (T). It is k = ln2/T = 0.693/T
T = 22 hours = 1320 min
The initial activity is
A = N0*k = (145,000)(0.693)/1320
= 76 decays/min