Speaker
Description
Neutron-capture reactions drive the synthesis of all elements heavier than iron. Unstable s-process branching isotopes are of particular interest: their neutron-capture cross sections, combined with isotopic analyses of primitive meteorites, uniquely constrain the physical conditions of AGB stars and the chemical evolution of our galaxy.
Measuring these cross sections experimentally remains one of the most demanding challenges in nuclear astrophysics, owing to the difficulties of producing radioactive samples of sufficient quality and activity, and to the extreme sensitivity and selectivity required to isolate the radiative capture channel. This contribution begins with an overview of s-process branching-point measurements carried out at CERN n_TOF, highlighting the astrophysical implications of recent studies and illustrating how successive beam upgrades and novel detector systems have enabled remarkable progress. Nonetheless, fundamental limitations persist: accessible half-lives are generally restricted to values above a few years, and covered neutron-energy ranges rarely extend beyond a few keV.
To overcome these barriers, a complementary and radically different approach is discussed, based on a free-neutron target integrated into a low-energy ion storage ring, enabling direct measurements of neutron-induced reactions on radioactive ions in inverse kinematics. Several neutron target designs are discussed, all based on a heavily moderated accelerator-driven neutron source. The synergy between conventional time-of-flight techniques at n_TOF and this inverse-kinematics methodology opens an unprecedented window, not only for s-process branching nuclei, but in the long term for the i- and r-process as well, which lie entirely beyond the reach of current direct experimental methods.