Production and Study of Neutron-rich Nuclei Using the LICORNE Directional Neutron Source
Acta. Phys. Pol. B
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 238U(n, f) reaction. This reaction and 232Th(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
235U(nth, f) and 252Cf(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 238U(n, f) fission yields and the structure of the 138Te and 100Sr 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.