1. The problem statement, all variables and given/known data An initially pure 3.4 g sample of Ga-67, an isotope with a half life of 78 hr. What is its initial decay rate? Note: Molar Mass values given in tables for chemical elements are for natural mix isotopic ratios. (i.e. the relative percentages of each isotope normally present in natural samples). The Molar Mass (in g/mol) for a pure isotope is equal to its atomic mass (in amu). (Answer in Bq, correct to 3 significant figures) Avogadro's Number = 6.022045*1023 g/mol Ga-67 = 66.9282049 u = 66.9282049 g/mol Half-life = T1/2 = 78 Hr 2. Relevant equations N = [ Avogadro's Number / 66.9282049 g/mol ] * 3.4 g λ = ln(2) / T1/2 Decay Rate = -λ*N 3. The attempt at a solution N = [ 6.022045*1023 g/mol / 66.9282049 g/mol ] * 3.4 g = 3.059241321 * 1022 λ = ln(2) / 280800 = 0.00000246847 Decay Rate = 0.00000246847 * 3.059241321 * 1022 = 7.5516454*1016 Bq = 7.55*1016 Bq (Correct to 3 sig figs) This doesn't seem correct. I've got the atomic mass and therefore the molar mass of Ga-67, but to calculate N (nuclei) should I have subtracted the electrons from the atomic mass / molar mass?