# How can you predict nuclear stability?

##### 1 Answer

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.

*NEUTRON/PROTON RATIO*

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.