a) In a sample of 1000 atoms, if 50 atoms decay in 5 s, what is the radioactivity, measured in mCi, of the sample?
b) In order to produce a level of radioactivity of 1mCi, how many nuclei of 99mTc (lambda=3.22x10^-5 s-1) must be present? What mass of the radionuclide does this correspond to?
c) A radioactive sample of 99mTc contains 10 mCi activity at 9 am. What is the radioactivity of the sample at 3 p.m. on the same day?