# What factors determine nuclear stability?

##### 1 Answer

The two main factors that determine nuclear stability are the neutron/proton ratio and the total number of nucleons in the nucleus.

*NEUTRON/PROTON RATIO*

The principal factor for determining whether a nucleus is stable is the neutron to proton ratio.

The graph below is a plot of the number of neutrons versus the number of protons in various stable isotopes. Stable nuclei with atomic numbers up to about 20 have an n/p ratio of about 1/1.

Above Z = 20, the number of neutrons always exceeds the number of protons in stable isotopes. The stable nuclei are located in the pink band known as the *belt of stability*. The belt of stability ends at lead-208.

*NUMBER OF NUCLEONS*

No nucleus higher than lead-208 is stable. That's because, although the nuclear strong force is about 100 times as strong as the electrostatic repulsions, it operates over only very short distances. When a nucleus reaches a certain size, the strong force is no longer able to hold the nucleus together.