How can you predict nuclear stability?
Most nuclei are stable if the neutron-to- proton ratio is between 1 and 1.5 and the total number of nucleons is less than 209.
At close distances, a strong nuclear force exists between nucleons. This attractive force comes from the neutrons. More protons in the nucleus need more neutrons to bind the nucleus together.
The graph below is a plot of the number of neutrons versus the number of protons in various stable isotopes.
The stable nuclei are in the pink band known as the belt of stability. They have a neutron/proton ratio between 1:1 and 1.5:1.
NUMBER OF NUCLEONS
The nuclear strong force operates over only short distances. When a nucleus is too big, the strong force is no longer able to hold the nucleus together. After 83-bismuth-209, all nuclei are unstable.