APS April meeting practice talks

Abstract:  Lisa Carpenter, NSCL - "Cluster Structure and Three-Body Decay in 14C" Abstract: Recent model calculations with most advanced methods for cluster states have shown the need of experimental data to probe the structure of light exotic nuclei, including those with α-clustering, such as 14C. The prototype Active Target Time Projection Chamber (pAT-TPC) allows us to investigate these types of structures, giving access to the full excitation function with a single beam energy. This type of experiment measures resonances in 14C that can be compared to the models. Additionally, using a Dalitz-type analysis, three-body decays can be analyzed to determine probabilities of "democratic" and "sequential" decay. The measurement was carried out by resonant alpha-scattering of a 10Be beam at 40 MeV delivered by the TwinSol facility at the University of Notre Dame. Preliminary results will be presented including event reconstruction using the Random Sample Consensus method. Sara Ayoub, NSCL - "SECAR: The Separator for Capture Reactions in Astrophysics" Abstract: Proton- and alpha-capture reactions on unstable proton-rich nuclei power astrophysical explosions like novae and X-ray bursts. Studying these processes is crucial to understanding the mechanisms behind those explosions and the nucleosynthesis at those sites. The Separator for Capture Reactions (SECAR) is a new recoil separator currently under construction at the National Superconducting Cyclotron Laboratory (NSCL) and the Facility for Rare Isotope Beams (FRIB) that will allow us to directly measure the astrophysical reaction rates of interest. It is designed to enable measurements with reaccelerated beams in the A$=-65 mass range over a broad range of astrophysical energies. Several of the magnets and other components are now installed at Michigan State University. The presentation will introduce the SECAR concept, its scientific goals, and provide an update of the current status of the project. SECAR is supported by the Department of Energy Office of Science Office of Nuclear Physics and the National Science Foundation. Rachel Titus, NSCL - "Impact of electron-captures on nuclei near N=50 on core-collapse supernovae" Abstract: Sensitivity studies of the late stages of stellar core collapse with respect to electron-capture rates indicate the importance of a region of nuclei near the N=50 shell closure, just above doubly magic 78Ni. In the present work, it has been demonstrated that uncertainties in key characteristics of the evolution, such as the lepton fraction, electron fraction, entropy, stellar density, and in-fall velocity are about 50% due to uncertainties in the electron-capture rates on nuclei in this region, although thousands of nuclei are included in the simulations. The present electron-capture rate estimates used for the nuclei in this region of interest are primarily based on a simple approximation, and it is shown that the estimated rates are likely overestimated by an order of magnitude or more. More accurate microscopic theoretical models are required to obtain Gamow-Teller strength distributions, upon which electron-capture rates are based. The development of these models and the benchmarking of such calculations rely on data from charge-exchange experiments at intermediate energies, and an experimental campaign to study N=50 nuclei with the (t,3He) reaction at NSCL will be presented. Steven A. Fromm, NSCL - "Improving the Optical Trapping Efficiency in the 225Ra Electric Dipole Moment Experiment via Monte Carlo Simulation" Abstract: In an effort to study and improve the optical trapping efficiency of the 225Ra Electric Dipole Moment experiment, a fully parallelized Monte Carlo simulation of the laser cooling and trapping apparatus was created at Argonne National Laboratory and now maintained and upgraded at Michigan State University. The simulation allows us to study optimizations and upgrades without having to use limited quantities of 225Ra (15 day half-life) in the experiment's apparatus. It predicts a trapping efficiency that differs from the observed value in the experiment by approximately a factor of thirty. The effects of varying oven geometry, background gas interactions, laboratory magnetic fields, MOT laser beam configurations and laser frequency noise were studied and ruled out as causes of the discrepancy between measured and predicted values of the overall trapping efficiency. Presently, the simulation is being used to help optimize a planned blue slower laser upgrade in the experiment's apparatus, which will increase the overall trapping efficiency by up to two orders of magnitude. Brent Glassman, NSCL- "β-delayed γ decay of 20Mg and the 19Ne(p,γ)20Na breakout reaction in Type I X-ray bursts"