Seminars

Tuesday, Nov 28 at 11:00 AM
NSCL Lecture Hall 1200
Jutta Escher, Lawrence Livermore National Laboratory
Capture Reactions on Unstable Isotopes: Determining Unknown Cross Sections with Indirect Data and Theory

Abstract:  Cross sections for compound-nuclear reactions involving unstable targets are important for many applications, but can often not be measured directly. Several indirect methods have recently been proposed to determine neutron capture cross sections for unstable isotopes. These methods aim at constraining statistical calculations of capture cross sections with data obtained from the decay of the compound nucleus relevant to the desired reaction. Each method produces this compound nucleus in a dierent manner (via a light-ion reaction, a photon-induced reaction, or decay) and requires additional ingredients to yield the sought-after cross-section. This talk focuses on the process of determining capture cross sections from inelastic scattering and transfer experiments. Specifically, theoretical descriptions of the (p,d) and (d,p) transfer reaction have been developed to complement recent measurements in the Zr-Y-Mo region. The procedure for obtaining constraints for unknown capture cross sections is illustrated. Indirectly extracted cross sections for both known (benchmark) and unknown capture reactions are presented. The main advantages and challenges of this approach are compared to those of the proposed alternatives. * This work is performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. Partial support from the Laboratory Directed Research and Development Program at LLNL,Project No. 16-ERD-022 is acknowledged.

Wednesday, Nov 29 at 4:10 PM
NSCL Lecture Hall 1200
Manuel Caamano Fresco, Universidade de Santiago de Compostela
Fission in Inverse Kinematics: A new window to experimental observables

Abstract:  Experimentally, the understanding of the complex, long, and intricate process of nuclear fission is approached by collecting as many observables as possible and from all fissioning systems available. The measured properties of the fissioning system and of the fission products, and their correlations, has led to the current picture where, in a very simplified way, the fission proceeds according certain modes or channels centred around fragments with particular numbers of protons and/or neutrons, which emerge with specific deformations that also drive the sharing of part of the available energy. Most of the information on fission was gathered so far in experiments that use direct kinematics, where the fissioning system can be considered at rest in the laboratory. However, these experiments suffer from two main drawbacks: few observables are measured simultaneously and the fragment atomic number is either absent or poor in resolution. The use of inverse kinematics, where the fissioning system is studied in-flight, opens a possibility to solve those issues and to add new information. In particular, we will discuss the use of magnetic spectrometers in order to provide the simultaneous measurement of the mass and atomic number of the fragments, as well as their velocities, which grants the access to the fissioning system reference frame. The correlation of the measured observables permits to recover properties such as the total kinetic energy or the neutron multiplicity that can be studied and compared with previous measurements. In addition, the measurement of the atomic number allows us to retrieve quantities such as the neutron-to-proton ratio of the fragments, the total excitation energy, and the elongation of the system can be calculated. From there, a few reasonable assumptions are enough to extract the intrinsic and collective excitation energy of the fragments as a function of their atomic number, along with their quadrupole deformation and their distance at scission. The discussion will mainly focus on the study of transfer- and fusion-induced fission of several systems, produced in inverse kinematics at GANIL (France). We will address the latest results on 240Pu and 250Cf, the ongoing analysis of the dependence with the fission energy, as well as future applications to the study of high-energy fission and quasi-fission.

Thursday, Nov 30 at 11:00 AM
NSCL Lecture Hall 1200
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HiP- Highlights in Progress
Friday, Dec 01 at 12:30 PM
1300 Auditorium (FRIB Tower 3)
Various Speakers,
Livestream - Talks and Panel Discussion: The Impact of the LIGO/VIRGO Neutron Star Merger Discovery on Research in Nuclear Science and Nuclear Astrophysics

Abstract:  Join nuclear scientists as they discuss the impact of the LIGO/VIRGO neutron star merger discovery and followup observations on nuclear science and nuclear astrophysics

Monday, Dec 04 at 11:00 AM
NSCL Lecture Hall 1200
Steven Ragnar Stroberg, Reed College
TBA

Abstract:  TBA

Tuesday, Dec 05 at 11:00 AM
Biomedical & Physical Sciences Bldg., Rm. 1400
Oleg Korobkin, Los Alamos National Laboratory
TBA

Abstract:  TBA

Wednesday, Dec 06 at 11:00 AM
Biomedical & Physical Sciences Bldg., Rm. 1400
Francesco Raimondi,
TBA

Abstract:  TBA

Thursday, Dec 07 at 10:30 AM
Biomedical & Physical Sciences Bldg., Rm. 1400
Saori Pastore, Los Alamos National Laboratory
TBA

Abstract:  TBA

Friday, Dec 08 at 11:00 AM
NSCL Lecture Hall 1200
Ingo Tews, Institute for Nuclear Theory, University of Washington, Seattle
Precision studies of nucleonic matter and nuclei

Abstract:  Neutron stars are astrophysical objects of extremes. They contain the largest reservoirs of degenerate fermions, reaching the highest densities we can observe in the cosmos. The observed two solar mass neutron stars place important constraints on the nuclear equation of state. In August the first neutron-star merger has been observed, which provided compelling evidence that these events are an important site for the production of neutron-rich heavy elements within the r-process; these nuclei will be probed in the new FRIB facility. Present predictions for these different strongly interacting systems are limited by our understanding of nuclear interactions, and our ability to make reliable calculations. An accurate description of such systems requires precise many-body methods in combination with a systematic theory for nuclear forces. In this talk I will explain how to use chiral effective field theory (EFT) and advanced Quantum Monte Carlo (QMC) many-body methods to provide a consistent and systematic approach to strongly interacting systems and allow precision studies with controlled theoretical uncertainties. Chiral EFT is a systematic framework for strong interactions based on the symmetries of Quantum Chromodynamics. It predicts two- and many-body interactions and allows to estimate theoretical uncertainties. On the other hand, QMC methods are among the most precise many-body methods available to study strongly interacting systems at finite densities. I will present recent results for light nuclei and the nucleonic matter relevant for the nuclear astrophysics of core-collapse supernovae, neutron stars, and neutron-star mergers, and will discuss future directions and opportunities.

Monday, Dec 11 at 12:30 PM
Biomedical & Physical Sciences Bldg., Rm. 1400
Alan Calder, Stonybrook University
The Quantification of Incertitude in Astrophysical Simulation Codes

Abstract:  We present a study of methodologies for the propagation of epistemic uncertainty, also known as incertitude, in complex astrophysical simulations. We chose the community simulation instrument MESA (Modules for Experiments in Stellar Astrophysics) and simulated the evolution of stars with a ZAMS mass of one solar mass. We explored the case of incertitude in stellar wind parameters, specifically parameters employed to model stellar winds during the red giant and asymptotic giant branch phases of evolution. These parameters are inputs to MESA, and we chose uncertainty intervals for each. Treating MESA as a ``black box,\" we applied two incertitude propagation techniques, Cauchy deviates and quadratic response surface models, to obtain bounds for white dwarf masses at the cessation of thermonuclear burning. These methodologies are applicable to other computational incertitude propagation problems.

Tuesday, Dec 12 at 11:00 AM
NSCL Lecture Hall 1200
Veronica Dexheimer, Kent State University
TBA

Abstract:  TBA