Production and Study of Neutron-rich Nuclei Using the LICORNE Directional Neutron Source

Abstract

We have recently successfully demonstrated a new technique for production and study of many of the most exotic neutron-rich nuclei at moderate spins. LICORNE, a newly developed directional inverse-kinematic fast neutron source at the IPN Orsay, was coupled to the MINIBALL high resolution γ-ray spectrometer to study nuclei the furthest from stability using the 238 U(n, f ) reaction. This reaction and 232 Th(n, f ) are the most neutron-rich fission production mechanisms achievable and can be used to simultaneously populate hundreds of neutron-rich nuclei up to spins of ≈ 16 . High selectivity in the experiment was achieved via triple γ-ray coincidences and the use of a 400 ns period pulsed neutron beam, a technique which is unavailable to other population mechanisms such as 235 U(n th , f ) and 252 Cf(SF). The pulsing allows time correlations to be exploited to separate delayed γ rays from isomeric states in the hundreds of nuclei produced, which are then used to cleanly select a particular nucleus and its exotic binary partners. In the recent experiment, several physics cases are simultaneously addressed such as shape coexistence, the evolution of shell closures far from stability, and the spectroscopy of nuclei in the r-process path near N = 82. Preliminary physics results on anomalies in the 238 U(n, f ) fission yields and the structure of the 138 Te and 100 Sr nuclei will soon be published. A future project, ν-ball, to couple LICORNE with a hybrid escape-suppressed spectrometer to refine further the technique and achieve a large increase in the observational limit is discussed.