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 inversekinematic fast neutron source at the ALTO facility of the IPN Orsay, was coupled to the MINIBALL γ-ray spectrometer to study very neutron rich nuclei 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 ~16h. 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 reaction mechanisms such as spontaneous fission. The pulsing allows time correlations to be exploited to separate delayed γ rays from isomeric states and supresses unwanted γ-rays from beta decay. In Autumn 2017, the ν-ball array will be operational at the ALTO facility of the IPN Orsay. This high efficiency hybrid Ge-LaBr3 spectrometer based around 24 clover Ge detectors, 10 co-axial Ge detectors and 20 LaBr3 scintillators will help to further refine the technique and achieve a large increase in the current observational limit.
Highlights
Theories of atomic nuclear stability suggest that up to ~7000 isotopes can exist in nature
Only around 4000 of these have been successfully synthesized in the laboratory
Information on excited states is important for those nuclei where none is currently available, and for those nuclei where only a handful of excited states are known, more complete information is needed on their nuclear structure in order to constrain nuclear models at the extremes of isospin and better understand the fundamental forces which hold nuclei together
Summary
Theories of atomic nuclear stability suggest that up to ~7000 isotopes can exist in nature. One mechanism to populate neutron-rich nuclei is nuclear fission at low excitation energy, where the curvature of the valley of stability guarantees that when a heavy nucleus splits in two fragments they will be produced, on average, with N/Z ratios significantly larger than those of the corresponding stable isotopes for these elements.
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