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"Recent activities for β-decay half-lives and β-delayed neutron emission of very neutron-rich isotopes"
Iris Dillmann, Daniel Abriola and Balraj Singh
Proc. of the "12th International Symposium on Origin of Matter and Evolution of Galaxies" (OMEG12), Tsukuba, Japan, November 18-21, 2013. Ed. by Sunchan Jeong, Nobuaki Imai, Hiroari Miyatake and Toshitaka Kajino
AIP Conf. Proc., Vol.1594 (2014) 332-338
ISBN: 978-0-7354-1228-6
Beta-delayed neutron (βn) emitters play an important, two-fold role in the stellar nucleosynthesis of heavy elements in the ”rapid neutron-capture process“ (r process). On one hand they lead to a detour of the material β-decaying back to stability. On the other hand, the released neutrons increase the neutron-to-seed ratio, and are re-captured during the freeze-out phase and thus influence the final solar r-abundance curve. A large fraction of the isotopes inside the r-process reaction path are not yet experimentally accessible and are located in the (experimental) ”Terra Incognita“. With the next generation of fragmentation and ISOL facilities presently being built or already in operation, one of the main motivation of all projects is the investigation of these very neutron-rich isotopes. A short overview of one of the planned programs to measure βn-emitters at the limits of the presently know isotopes, the BRIKEN campaign (Beta delayed neutron emission measurements at RIKEN) will be given. Presently, about 600 β-delayed one-neutron emitters are accessible, but only for a third of them experimental data are available. Reaching more neutron-rich isotopes means also that multiple neutron-emission becomes the dominant decay mechanism. About 460 β-delayed two-, three-or four-neutron emitters are identified up to now but for only 30 of them experimental data about the neutron branching ratios are available, most of them in the light mass region below A=30. The International Atomic and Energy Agency (IAEA) has identified the urgency and picked up this topic recently in a ”Coordinated Research Project“ on a ”Reference Database for Beta-Delayed Neutron Emission Data“. This project will review, compile, and evaluate the existing data for neutron-branching ratios and half-lives of β-delayed neutron emitters and help to ensure a reliable database for the future discoveries of new isotopes and help to constrain astrophysical and theoretical models.
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