Nuclear drip line

A boundary in the chart of nuclides beyond which adding a proton or neutron produces a nucleus unstable to immediate particle emission.

Nuclear separation energy: The energy required to remove one or more nucleons from a nucleus. A zero or negative separation energy signals that a nucleon can escape without an energy cost.
Nuclide: A species of atom specified by its numbers of protons and neutrons. Each point near a drip line represents a nuclide with a particular nucleon count.
Radioactive ion beam: A beam of short-lived atomic nuclei used in experiments on unstable isotopes. Such beams make measurements of nuclei close to the drip lines possible.
Ab initio nuclear theory: Methods that calculate nuclear properties from nucleon interactions with controlled approximations. Predictions for unmeasured drip-line nuclei test how well nuclear forces are understood.
Nuclear binding energy: The energy needed to separate a nucleus completely into its constituent protons and neutrons. Binding energy underlies the stability changes that locate the drip lines.
Isotope: One of several nuclides of the same element, differing in neutron number. Moving across isotopes changes neutron number and can approach the neutron drip line.
Rare isotope facility: An accelerator laboratory designed to produce and study uncommon radioactive nuclei. These facilities extend experimental access toward the limits of nuclear binding.
Nuclear force: The effective interaction among protons and neutrons that governs nuclear structure and reactions. Uncertainty in its poorly constrained components propagates into drip-line predictions.
Proton emission: Radioactive decay in which a proton escapes directly from an energetically unbound nucleus. This is the characteristic particle-loss process beyond the proton drip line.
Proton: A positively charged subatomic particle found in atomic nuclei. The proton drip line marks the limit to adding protons while retaining a bound nucleus.

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