The BRIKEN project: extensive new beta- delayed neutron measurements for astrophysics

Jose Tain, University of Valencia
Monday, Feb 11, 12:30 PM - JINA-CEE Pizza Lunch
1400 Biomedical and Physical Sciences Building

Abstract:  Beta delayed-neutron emission occurs for sufficiently neutron-rich nuclei when the decay populates states above the neutron separation energy in the daughter nucleus. It was discovered in fission- products soon after fission itself and it plays a key role in the control of nuclear reactors. The importance of this phenomenon in the description of rapid neutron capture (r-) processes occurring in explosive stellar scenarios with large neutron abundances was first pointed out in the seventies. The initial effect is the displacement to lower masses of the distribution of elements synthetized along the r-process path. In addition the delayed neutrons reactivate the neutron capture reactions with the opposite effect. The computation of the final isotopic abundances requires the knowledge of decay properties for very neutron-rich nuclei that have eluded until now direct experimental investigation. The BRIKEN project was launched to extend significantly our knowledge of beta-delayed neutron emission probabilities (Pn) and half-­‐lives (T 1/2) into this region, combining the very high beam intensity achieved at the RIBF accelerator complex in RIKEN and the selection/identification capabilities for reaction products of the BigRIPS in-flight spectrometer, together with state-of-the-art ion implant- and- decay detectors and moderated neutron counters. The experimental program started in 2017 and envisages the measurement of over 250 new beta-delayed neutron emitters, and 100 new half-lives covering the region from mass A~70 to A~200 with a direct impact in r-process nucleosynthesis calculations. Lighter mass (A=30-70) nuclei will also be investigated. The wealth of new data will allow a thorough benchmarking of nuclear structure dependent beta-strength calculations and the study of the competition between gamma-emission and different multi-neutron emission channels. In this presentation I will review the status of the experimental program and show some initial results.