A sample of pure 99mTc is obtained and has an activity of 5000MBq. What will be the approximate change in mass of this sample after it has all decayed to 99Tc (assume no further decay from this state).
(Avogadro's number = 6.023x1023 per mole; Half life of 99mTc = 6Hrs. Assume all 99mTc decays by the emission of 140keV gamma rays )
N/N0 = e-zt,
N*mass number/avogado number = mass of nuclei
N= number of atoms remaining
The Attempt at a Solution
Used halflife= ln2/z to work out the decay constant = 3.2 * 10^-5
A/z= N so, 5*10^9/3.2 * 10^-5 = 1.56*10^14 = N
Dont know if this is correct or what to do from here.... thanks.