neutron drip line

The neutron drip line is a boundary in nuclear physics that marks the limit of how many neutrons can be added to an atom's nucleus before they start “dripping” off, meaning they can no longer be held tightly. Beyond this line, extra neutrons don't stay bound and escape the nucleus naturally. It defines the edge of possible exotic isotopes, helping scientists understand the stability and structure of atomic nuclei, especially for very heavy or neutron-rich elements. Essentially, it shows the maximum neutron number that an isotope can have for a given element.