1. The problem statement, all variables and given/known data Analysis of the material shows that it contains both Gallium-64 (atomic mass = 63.936838u) and Zinc-64 (atomic mass = 63.929147u). Which nuclide is the parent nuclide and which is the daughter nuclide? 2. Relevant equations N/A 3. The attempt at a solution The answer is supposed to be Ga-64. How can we tell it is Ga-64 if we are not given if it is beta plus or beta minus? Is it because we are supposed to assume that the decay will spontaneously happen? So that it will release the energy and go from a higher mass to a lower mass? But we dont know if someone bombarded energy to it or not... I was just wondering how you would look at this kind of problem. Thanks for your help.