Define radioactive decay constant.
Show that the decay constant 
is related to the half-life 
of a radioactive isotope by the expression
A small volume of solution containing the radioactive isotope sodium-24 (
) has an initial activity of 
. Sodium-24, of half-life 15 hours, decays to form a stable daughter isotope. All of the solution is poured into a container of water. After 36 hours, a sample of water of volume 
, taken from the container, is found to have an activity of 
. Assuming that the solution of the radioactive isotope is distributed uniformly throughout the container of water, calculate the volume of water in the container.
.
