Where Nuclear, Atomic and Astrophysics Meet: Beta Decay of Highly Charged Ions

Ionization Alters Cosmic Nucleosynthesis

Beta decay transforms neutrons into protons inside atomic nuclei, playing a central role in creating elements heavier than iron. Standard measurements use neutral atoms, but in stellar interiors—where temperatures reach billions of degrees—atoms lose most or all electrons, becoming highly charged ions. This ionization opens new decay channels, notably bound-state beta decay, where the emitted electron occupies an orbital in the daughter ion rather than escaping as a free particle. Such changes can shorten half-lives by orders of magnitude or suppress certain decays, directly influencing neutron-capture processes that build heavy nuclei.

The rapid neutron-capture process, or r-process, occurs in explosive environments like neutron star mergers and certain supernovae, producing roughly half the elements heavier than iron. Beta decays pace the conversion of neutron-rich nuclei toward stability after neutron captures saturate. In the hot, dense plasma of these sites, high ionization modifies these rates, yet most nuclear databases rely on neutral-atom values. Discrepancies between simulated and observed abundances—particularly in rare-earth elements and actinides—persist partly because of these unaccounted effects.

Facilities such as the Experimental Storage Ring at GSI in Darmstadt have pioneered storage and observation of radioactive highly charged ions in ultra-high vacuum, preserving charge states long enough for decay measurements. Recent work includes half-life studies of exotic nuclei and probes of rare modes like nuclear excitation via electron capture. New setups, including trap-based experiments at places like TITAN at TRIUMF and proposed facilities like PANDORA, target light and heavy ions to quantify plasma effects on decay. These efforts coincide with advances in multi-messenger astronomy, where gravitational-wave detections and kilonova light curves demand accurate nucleosynthesis yields to interpret element production in real-time cosmic events.

Tensions arise between atomic and nuclear physics communities in modeling these intertwined effects, as well as between theorists predicting resonance conditions for exotic decays and experimentalists struggling to observe them unambiguously. Costs remain modest compared to accelerator upgrades, but delays in data collection risk outdated models as new astrophysical observations accumulate.