Grant: Subatomic Physics Envelope - Individual

Beta-delayed neutron 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 beta-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. Two important physical quantities can be measured at once with bn-emitters: the half-life of the precursor, and the beta-strength above the neutron separation energy can be deduced from the neutron-branching ratio.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, one of the main motivation of all projects is the investigation of these very neutron-rich isotopes. Presently, about 600 one-neutron emitters are known, but only for a third of them experimental data is available. However, reaching more neutron-rich isotopes means also that multiple neutron-emission becomes the dominant decay mechanism. About 460 beta-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 4-year ?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 beta-delayed neutron emitters. This will help to ensure a reliable database for the future discoveries of new isotopes and help to constrain astrophysical and theoretical models. TRIUMF has taken a lead role in this and has submitted an extensive proposal with Canadian colleagues from McMaster University and the University of Guelph for future measurements and the evaluation of existing data.This Discovery Grant application aims to investigate beta-delayed neutron-emitters with several detectors and novel techniques at different world-leading facilities.One direction is the use of the ?standard? method with 3He-filled neutron detectors to measure directly the branching ratio and half-lives. This research will be conducted with highly-efficient detector setups and state-of-the-art electronics. The ""BRIKEN campaign"" at RIKEN/ Japan proposes to perform experiments in 2014-16 with the most efficient neutron detector setup worldwide. Under my leadership TRIUMF is involved in this campaign and will submit proposals for measurements on astrophysical key nuclides.After the BRIKEN campaign the existing program at the present ISAC-1 facility at TRIUMF will be extended towards more neutron-rich beams which are expected with the new ARIEL facility in a few years. We propose to carry out high-precision branching-ratio measurements for nuclear structure and r-process studies.The second direction is the development of novel techniques to measure neutron-branching ratios circumventing the detection of the neutron. One of the proposed methods uses traps to measure the branching ratio and neutron energy spectra via the beta-recoil ion coincidence technique. This method has recently been successfully employed by an Argonne/ Livermore collaboration. The advantages and disadvantages of this method will be investigated with both traps at TRIUMF (TITAN and TRINAT). The additional installation of neutron detectors can expand this method to multi-neutron emitters.