HELP on BINDING ENERGY/NUCLEON (usually expressed in electron volts, eV)
The mass of an isotope is not simply the sum of the masses of all the constituent protons and neutrons within the nucleus, because when they are all gathered together inside the nucleus, some of the mass (energy) is 'lost' and this loss is called the binding energy, which holds all the nucleons together and is responsible for the stability of the nucleus. If the total binding energy of the nucleus is divided by the number of nucleons (protons plus neutrons) within the nucleus, then this is the binding energy per nucleon. This value is small for elements of low atomic number (number of protons), but rapidly climbs to a slowly drooping plateau of 8 million electron volts per nucleon. Iron-56 and nickel-56 have the highest values, and are thus the most stable elements; elements above iron can split into two (fission) releasing energy (as in uranium), and elements below iron can combine (fusion) also releasing energy (as in the hydrogen bomb). Here, the BE/N is average value for the natural mixture of isotopes of that element.
In the "TABLE' plot of 'NATURALLY RADIOACTIVE' elements, when it says '1 x 10éï % of it active', it actually means just a trace of one isotope, and NOT 10éï. Also, when it says '4 x 10éï % of it active', it means there are four radioactive isotopes which exist in trace amounts.
