protonrich

Protonrich is a descriptor used in nuclear physics to denote nuclides with a higher fraction of protons than neutrons. Proton-rich nuclei lie near the proton drip line on the chart of nuclides, and for many isotopes the neutron number N is smaller than the proton number Z. These nuclei are typically unstable and decay toward the valley of stability by beta-plus decay or electron capture, effectively converting a proton into a neutron and emitting a positron or neutrino.

Some extremely proton-rich systems may exhibit other decay modes, such as two-proton emission, when energetically allowed.

Proton-rich nuclides are studied using high-energy nuclear reactions, such as projectile fragmentation, fusion-evaporation, spallation, and via on-line mass separators. Their properties, including masses, half-lives, and decay schemes, are measured with charged-particle detectors, gamma spectroscopy, and implantation detectors. Due to short half-lives, experiments require rapid production and separation.

Understanding proton-rich nuclei informs nuclear structure theories, isospin symmetry, and the limits of nuclear existence. In astrophysics, proton-rich isotopes are relevant to nucleosynthesis pathways such as the rapid proton capture process (rp-process) that operates in explosive hydrogen-rich environments; reaction rates and beta-decay lifetimes of waiting-point nuclei influence element production in X-ray bursts.

Challenges include very short lifetimes, sparse data, and large theoretical uncertainties in modeling near the proton drip line, where Coulomb forces and shell effects play significant roles. Ongoing and future facilities aim to map the proton-rich region more completely to test nuclear models and illuminate nucleosynthesis pathways.