Seminars

Tuesday, Jul 14 at 11:30 AM
Online via Zoom
Saori Pastore, Washington University in St. Louis
FRIB TA - Dialogues on Nuclear Physics: Electroweak interactions in nuclei

Abstract:  Hosts: Baha Balantekin and Vincenzo Cirigliano

Tuesday, Jul 14 at 1:00 PM
Online via Zoom
Yuchen Cao, NSCL Graduate Research Assistant
Quantified large-scale density functional theory predictions of nuclear properties

Abstract:  Committee: Witold Nazarewicz (Chairperson), Scott Bogner, Sean Couch, Kendall Mahn, Jaideep Singh. Thesis is available at https://pa.msu.edu/academics/graduate-program/current-graduate-students/ - Select student name

Wednesday, Jul 15 at 11:00 AM
Online via Zoom
Jose Javier Valiente Dobon, National Institute for Nuclear Physics
Manifestation of the Berry phase in the atomic nucleus 213Pb

Abstract:  In this seminar I will present some of our later results on the 213Pb neutron-rich nucleus studied using the unique availability of a primary 1 GeV A 238U beam and of the FRS-RISING setup at GSI. The products of the uranium fragmentation were separated in mass and atomic number and then implanted for isomer decay [gamma]-ray spectroscopy. A level scheme from the decay of the spin and parity 21/2+ isomer, based on [gamma] intensities, [gamma]-[gamma] coincidences and state lifetimes was built up and the E2 transition probabilities from the spin and parity 21/2+ isomer to two low-lying spin and parity17/2+ levels were also deduced. This experimental data has evidenced one of the best examples of a semi-magic nucleus with a half-filled isolated single-j shell where seniority selection rules are obeyed to a very good approximation. In the most simple shell-model approach 213Pb can be described as five neutrons in the orbital g9/2 on top of the 208Pb core. Large scale shell-model calculations in the full valence space beyond 208Pb confirm that although the orbital g9/2 is not isolated in energy, it is found to carry the dominant component in the wave function of the low-energy states. The experimental level scheme and the reduced transition probabilities are in good agreement with the theoretical description that predicts the existence of two spin and parity 17/2+ levels of a very different nature: one with seniority 3, while the other with seniority 5. The absence of mixing between the two spin and parity 17/2+ states follows from the self-conjugate character of 213Pb, where the particle-hole transformation defines an observable Berry phase that leads to the conservation of seniority for most but not all states in this nucleus. The Berry phase [1], which is a gauge-invariant geometrical phase accumulated by the wavefunction along a closed path, is a class of observables that are not associated with any operator. It is a key feature in quantum-mechanical systems, that has far reaching consequences, and has been found in many fields of physics since its postulation in the eighties. In the atomic self-conjugate nucleus 213Pb, the quantized Berry phase is evidenced by the conservation of seniority under the particle-hole conjugation transformation. In atomic nuclei no experimental signature of the Berry phase was reported up to now. [1] M. V. Berry, Proc. Roy. Soc. A392, 45 (1984).

Thursday, Jul 16 at 2:00 PM
Online via Zoom
Hao Lin, NSCL Graduate Research Assistant
Time-dependent description of heavy-ion collisions

Abstract:  Committee: Pawel Danielewicz (Chairperson), Morten Hjorth-Jensen, Filomena Nunes, Carlo Piermarocchi, Man-Yee Betty Tsang, Gary Westfall. Thesis is available for review at https://pa.msu.edu/academics/graduate-program/current-graduate-students/ - Select student name

Wednesday, Jul 22 at 11:00 AM
Online via Zoom
Stephane Goriely, Universite Libre de Bruxelles
Nucleosynthesis in neutron-star mergers and related nuclear physics

Abstract:  One of the major issues in modern astrophysics concerns the analysis and understanding of the present composition of the Universe and its various constituting objects. Nucleosynthesis models aim to explain the origin of the different nuclei observed in nature by identifying the possible processes able to synthesize them. Though the origin of most of the nuclides lighter than iron through the various hydrostatic and explosive burning stages in stars is now quite well understood, the synthesis of the heavy elements (i.e. heavier than iron) remains obscure in many respects. In particular, the rapid neutron-capture process, or r-process, is known to be of fundamental importance for explaining the origin of approximately half of the A>60 stable nuclei observed in nature. The r-process was believed for long to develop during the explosion of a star as a type II supernova but recent observations tend to favour the merging of two compact objects. The recent observation of the binary neutron star (NS) merger GW170817 and its corresponding optical kilonova counterpart suggest that neutron star mergers are the dominant source of r-process production in the Universe. Comprehensive nucleosynthesis calculations based on sophisticated multidimensional relativistic simulations show that the combined contributions from both the dynamical (prompt) ejecta expelled during NS-NS or NS-black hole (BH) mergers, and the neutrino and viscously driven outflows generated during the post-merger remnant evolution of relic neutron stars or BH-torus systems can lead to the production of r-process elements from Zr (A ≥ 90) up to thorium and uranium with an abundance distribution that reproduces extremely well the solar distribution, as well as the elemental distribution observed in low-metallicity stars. The stellar nucleosynthesis requires a detailed knowledge not only of the astrophysical sites and physical conditions in which the processes take place, but also the nuclear structure and interaction properties for all the nuclei involved. Both the astrophysical and nuclear physics aspects of the r-process nucleosynthesis in neutron star mergers will be discussed with a special attention paid to major open questions affecting our understanding of the r-process nucleosynthesis.

Tuesday, Jul 28 at 11:30 AM
Online via Zoom
Katerina Chatziioannou, Flatiron Institute
FRIB TA - Dialogues on Nuclear Physics: Challenges in nuclear structure theory

Abstract:  Hosts: Alex Gade, Charlotte Elster, Sanjay Reddy, Jorge Piekarewicz