Nuclear Astrophysics

A new path to element formation

A new path to element formation: IRIS’ first results give astrophysicists and nuclear physicists a deeper understanding of the nuclear states and pathways involved in element formation. As reported in Physical Review Letters (2015), the results provide the experimental evidence for a new kind of nuclear excitation, soft dipole resonance. IRIS researchers identified this resonance in neutron-rich lithium-11 (11Li), the heaviest bound lithium isotope, with three protons and eight neutrons, two of which orbit, barely held, in a halo, far from the nuclear core. Oscillation of the halo neutrons, the experiment revealed, leads to an extremely brief, quasi-bound nuclear resonance state, significantly changing the potential for neutron capture, as occurs in stars during element formation. The results confirm theoretical predictions and provide an important path for developing new nuclear models to predict the properties of neutron-rich isotopes.