THE ATOM

1. Law of Radioactive Decay
   
   
   where  is the activity, or rate of decay,  is the decay constant and N the number of undecayed nuclei.
2. 
   
   where  is the half-life of a radioactive isotope and  is the decay constant.
3. Avogadro’s Number
   
   Note: the mass of any element expressed in grams, e.g. 12g of carbon, contains this number of atoms.
4. 
   where E is the energy lost / gained when there is a mass excess / deficit m in a reaction and c is the speed of light in vacuo.
5. Pair Production
   
6. Pair Annihilation